Linux.協議棧分析.socket
SYSCALL_DEFINE3(socket, int, family, int, type, int, protocol)
{
int retval;
struct socket *sock;
int flags;
/* Check the SOCK_* constants for consistency. */
BUILD_BUG_ON(SOCK_CLOEXEC != O_CLOEXEC);
BUILD_BUG_ON((SOCK_MAX | SOCK_TYPE_MASK) != SOCK_TYPE_MASK);
BUILD_BUG_ON(SOCK_CLOEXEC & SOCK_TYPE_MASK);
BUILD_BUG_ON(SOCK_NONBLOCK & SOCK_TYPE_MASK);
flags = type & ~SOCK_TYPE_MASK;
if (flags & ~(SOCK_CLOEXEC | SOCK_NONBLOCK))
SYSCALL_DEFINE3(socket, int, family, int, type, int, protocol)
{
int retval;
struct socket *sock;
int flags;
/* Check the SOCK_* constants for consistency. */
BUILD_BUG_ON(SOCK_CLOEXEC != O_CLOEXEC);
BUILD_BUG_ON((SOCK_MAX | SOCK_TYPE_MASK) != SOCK_TYPE_MASK);
BUILD_BUG_ON(SOCK_CLOEXEC & SOCK_TYPE_MASK);
BUILD_BUG_ON(SOCK_NONBLOCK & SOCK_TYPE_MASK);
flags = type & ~SOCK_TYPE_MASK;
if (flags & ~(SOCK_CLOEXEC | SOCK_NONBLOCK))
SYSCALL_DEFINE3(socket, int, family, int, type, int, protocol)
{
int retval;
struct socket *sock;
int flags;
/* Check the SOCK_* constants for consistency. */
BUILD_BUG_ON(SOCK_CLOEXEC != O_CLOEXEC);
BUILD_BUG_ON((SOCK_MAX | SOCK_TYPE_MASK) != SOCK_TYPE_MASK);
BUILD_BUG_ON(SOCK_CLOEXEC & SOCK_TYPE_MASK);
BUILD_BUG_ON(SOCK_NONBLOCK & SOCK_TYPE_MASK);
flags = type & ~SOCK_TYPE_MASK;
if (flags & ~(SOCK_CLOEXEC | SOCK_NONBLOCK))
|
1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294 1295 1296 1297 1298 1299 1300 1301 |
SYSCALL_DEFINE3(socket, int, family, int, type, int, protocol) { int retval; struct socket *sock; int flags;
/* Check the SOCK_* constants for consistency. */ BUILD_BUG_ON(SOCK_CLOEXEC != O_CLOEXEC); BUILD_BUG_ON((SOCK_MAX | SOCK_TYPE_MASK) != SOCK_TYPE_MASK); BUILD_BUG_ON(SOCK_CLOEXEC & SOCK_TYPE_MASK); BUILD_BUG_ON(SOCK_NONBLOCK & SOCK_TYPE_MASK);
flags = type & ~SOCK_TYPE_MASK; if (flags & ~(SOCK_CLOEXEC | SOCK_NONBLOCK)) return -EINVAL; type &= SOCK_TYPE_MASK;
if (SOCK_NONBLOCK != O_NONBLOCK && (flags & SOCK_NONBLOCK)) flags = (flags & ~SOCK_NONBLOCK) | O_NONBLOCK;
retval = sock_create(family, type, protocol, &sock); if (retval < 0) goto out;
retval = sock_map_fd(sock, flags & (O_CLOEXEC | O_NONBLOCK)); if (retval < 0) goto out_release;
out: /* It may be already another descriptor 8) Not kernel problem. */ return retval;
out_release: sock_release(sock); return retval; } |
SYSCALL_DEFINE3(socket, int, family, int, type, int, protocol)
{
int retval;
struct socket *sock;
int flags;
/* Check the SOCK_* constants for consistency. */
BUILD_BUG_ON(SOCK_CLOEXEC != O_CLOEXEC);
BUILD_BUG_ON((SOCK_MAX | SOCK_TYPE_MASK) != SOCK_TYPE_MASK);
BUILD_BUG_ON(SOCK_CLOEXEC & SOCK_TYPE_MASK);
BUILD_BUG_ON(SOCK_NONBLOCK & SOCK_TYPE_MASK);
flags = type & ~SOCK_TYPE_MASK;
if (flags & ~(SOCK_CLOEXEC | SOCK_NONBLOCK))
return -EINVAL;
type &= SOCK_TYPE_MASK;
if (SOCK_NONBLOCK != O_NONBLOCK && (flags & SOCK_NONBLOCK))
flags = (flags & ~SOCK_NONBLOCK) | O_NONBLOCK;
retval = sock_create(family, type, protocol, &sock);
if (retval < 0)
goto out;
通過查看socket的幫助手冊可以得到socket的定義形式爲：
int socket(int domain, int type, int protocol);
C
int socket(int domain, int type, int protocol);
domain的有效值如下:
AF_UNIX, AF_LOCAL Local communication unix(7)
AF_INET IPv4 Internet protocols ip(7)
AF_INET6 IPv6 Internet protocols ipv6(7)
AF_IPX IPX - Novell protocols
AF_NETLINK Kernel user interface device netlink(7)
AF_X25 ITU-T X.25 / ISO-8208 protocol x25(7)
AF_AX25 Amateur radio AX.25 protocol
AF_ATMPVC Access to raw ATM PVCs
AF_APPLETALK Appletalk ddp(7)
AF_PACKET Low level packet interface packet(7)
而type的取值範圍爲:
SOCK_STREAM Provides sequenced, reliable, two-way, connection-based
byte streams. An out-of-band data transmission mecha‐
nism may be supported.
SOCK_DGRAM Supports datagrams (connectionless, unreliable messages
of a fixed maximum length).
SOCK_SEQPACKET Provides a sequenced, reliable, two-way connection-
based data transmission path for datagrams of fixed
maximum length; a consumer is required to read an
entire packet with each input system call.
SOCK_RAW Provides raw network protocol access.
SOCK_RDM Provides a reliable datagram layer that does not guar‐
antee ordering.
SOCK_PACKET Obsolete and should not be used in new programs; see
packet(7).
而type的取值範圍爲:
SOCK_STREAM Provides sequenced, reliable, two-way, connection-based
byte streams. An out-of-band data transmission mecha‐
nism may be supported.
SOCK_DGRAM Supports datagrams (connectionless, unreliable messages
of a fixed maximum length).
SOCK_SEQPACKET Provides a sequenced, reliable, two-way connection-
based data transmission path for datagrams of fixed
maximum length; a consumer is required to read an
entire packet with each input system call.
SOCK_RAW Provides raw network protocol access.
SOCK_RDM Provides a reliable datagram layer that does not guar‐
antee ordering.
SOCK_PACKET Obsolete and should not be used in new programs; see
packet(7).
而在內核版本2.6.27之後，還可以通過設定相應二進制爲1來設定socket的類型。即type可以在取上述值後再按位OR以下值。這一點可以在socket進入內核的源代碼中得到證實。
SOCK_NONBLOCK Set the O_NONBLOCK file status flag on the new open
file description. Using this flag saves extra calls to
fcntl(2) to achieve the same result.
SOCK_CLOEXEC Set the close-on-exec (FD_CLOEXEC) flag on the new file
descriptor. See the description of the O_CLOEXEC flag
in open(2) for reasons why this may be useful.
protocol一般爲0。
socket函數經過前述的方式進入內核後會最終由sys_socket(net/socket.c)來完成。
C
1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294 1295 1296 1297 1298 1299 1300 1301 |
SYSCALL_DEFINE3(socket, int, family, int, type, int, protocol) { int retval; struct socket *sock; int flags; /* Check the SOCK_* constants for consistency. */ BUILD_BUG_ON(SOCK_CLOEXEC != O_CLOEXEC); BUILD_BUG_ON((SOCK_MAX | SOCK_TYPE_MASK) != SOCK_TYPE_MASK); BUILD_BUG_ON(SOCK_CLOEXEC & SOCK_TYPE_MASK); BUILD_BUG_ON(SOCK_NONBLOCK & SOCK_TYPE_MASK); flags = type & ~SOCK_TYPE_MASK; if (flags & ~(SOCK_CLOEXEC | SOCK_NONBLOCK)) return -EINVAL; type &= SOCK_TYPE_MASK; if (SOCK_NONBLOCK != O_NONBLOCK && (flags & SOCK_NONBLOCK)) flags = (flags & ~SOCK_NONBLOCK) | O_NONBLOCK; retval = sock_create(family, type, protocol, &sock); if (retval < 0) goto out; retval = sock_map_fd(sock, flags & (O_CLOEXEC | O_NONBLOCK)); if (retval < 0) goto out_release; out: /* It may be already another descriptor 8) Not kernel problem. */ return retval; out_release: sock_release(sock); return retval; } |
1278~1281行就是取得type的值並檢查是否合法。
1278~1281行就是取得type的值並檢查是否合法。
我們知道socket對於用戶的而言就是一個已經打開的特殊文件，而內核則爲插口(socket)定義了一種特殊的文件類型形成特殊的文件系統sockfs(net/socket.c)，而sys_socket中調用的兩個函數sock_create和sock_map_fd，可以看到這兩個函數都共用一個sock參數，這便是爲內核管理socket用的，而sock_map_fd明顯是爲用戶提供已經打開的文件號。
sockfs的建立過程省略，sockfs的定義如下：
C
|
301 302 303 304 305 306 307 |
static struct vfsmount *sock_mnt __read_mostly;
static struct file_system_type sock_fs_type = { .name = "sockfs", .get_sb = sockfs_get_sb, .kill_sb = kill_anon_super, }; |
而所謂的通過socket函數創建一個插口，就是在sockfs中創建一個特殊文件，或者說是一個結點，併爲實現相應插口功能建立一起一整套數據結構。所以首先就通過sock_create創建一個struct socket數據結構，然後通過sock_map_fd映射到一個已經打開的文件上。在分析sock_create和sock_map_fd之前先看看struct socket的定義
我們知道socket對於用戶的而言就是一個已經打開的特殊文件，而內核則爲插口(socket)定義了一種特殊的文件類型形成特殊的文件系統sockfs(net/socket.c)，而sys_socket中調用的兩個函數sock_create和sock_map_fd，可以看到這兩個函數都共用一個sock參數，這便是爲內核管理socket用的，而sock_map_fd明顯是爲用戶提供已經打開的文件號。
sockfs的建立過程省略，sockfs的定義如下：
C
301 302 303 304 305 306 307 |
static struct vfsmount *sock_mnt __read_mostly; static struct file_system_type sock_fs_type = { .name = "sockfs", .get_sb = sockfs_get_sb, .kill_sb = kill_anon_super, }; |
而所謂的通過socket函數創建一個插口，就是在sockfs中創建一個特殊文件，或者說是一個結點，併爲實現相應插口功能建立一起一整套數據結構。所以首先就通過sock_create創建一個struct socket數據結構，然後通過sock_map_fd映射到一個已經打開的文件上。在分析sock_create和sock_map_fd之前先看看struct socket的定義(include/linux/net.h)：
C
118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 |
/** * struct socket - general BSD socket * @state: socket state (%SS_CONNECTED, etc) * @type: socket type (%SOCK_STREAM, etc) * @flags: socket flags (%SOCK_ASYNC_NOSPACE, etc) * @ops: protocol specific socket operations * @fasync_list: Asynchronous wake up list * @file: File back pointer for gc * @sk: internal networking protocol agnostic socket representation * @wait: wait queue for several uses */ struct socket { socket_state state; kmemcheck_bitfield_begin(type); short type; kmemcheck_bitfield_end(type); unsigned long flags; /* * Please keep fasync_list & wait fields in the same cache line */ struct fasync_struct *fasync_list; wait_queue_head_t wait; struct file *file; struct sock *sk; const struct proto_ops *ops; }; |
C
155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 |
struct proto_ops { int family; struct module *owner; int (*release) (struct socket *sock); int (*bind) (struct socket *sock, struct sockaddr *myaddr, int sockaddr_len); int (*connect) (struct socket *sock, struct sockaddr *vaddr, int sockaddr_len, int flags); int (*socketpair)(struct socket *sock1, struct socket *sock2); int (*accept) (struct socket *sock, struct socket *newsock, int flags); int (*getname) (struct socket *sock, struct sockaddr *addr, int *sockaddr_len, int peer); unsigned int (*poll) (struct file *file, struct socket *sock, struct poll_table_struct *wait); int (*ioctl) (struct socket *sock, unsigned int cmd, unsigned long arg); int (*compat_ioctl) (struct socket *sock, unsigned int cmd, unsigned long arg); int (*listen) (struct socket *sock, int len); int (*shutdown) (struct socket *sock, int flags); int (*setsockopt)(struct socket *sock, int level, int optname, char __user *optval, unsigned int optlen); int (*getsockopt)(struct socket *sock, int level, int optname, char __user *optval, int __user *optlen); int (*compat_setsockopt)(struct socket *sock, int level, int optname, char __user *optval, unsigned int optlen); int (*compat_getsockopt)(struct socket *sock, int level, int optname, char __user *optval, int __user *optlen); int (*sendmsg) (struct kiocb *iocb, struct socket *sock, struct msghdr *m, size_t total_len); int (*recvmsg) (struct kiocb *iocb, struct socket *sock, struct msghdr *m, size_t total_len, int flags); int (*mmap) (struct file *file, struct socket *sock, struct vm_area_struct * vma); ssize_t (*sendpage) (struct socket *sock, struct page *page, int offset, size_t size, int flags); ssize_t (*splice_read)(struct socket *sock, loff_t *ppos, struct pipe_inode_info *pipe, size_t len, unsigned int flags); }; |
接下來分析sock_create(net/socket.c)，sock_create會調用__sock_create。
C
1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252 1253 1254 1255 1256 1257 1258 1259 |
static int __sock_create(struct net *net, int family, int type, int protocol, struct socket **res, int kern) { int err; struct socket *sock; const struct net_proto_family *pf; /* * Check protocol is in range */ if (family < 0 || family >= NPROTO) return -EAFNOSUPPORT; if (type < 0 || type >= SOCK_MAX) return -EINVAL; /* Compatibility. This uglymoron is moved from INET layer to here to avoid deadlock in module load. */ if (family == PF_INET && type == SOCK_PACKET) { static int warned; if (!warned) { warned = 1; printk(KERN_INFO "%s uses obsolete (PF_INET,SOCK_PACKET)\n", current->comm); } family = PF_PACKET; } err = security_socket_create(family, type, protocol, kern); if (err) return err; /* * Allocate the socket and allow the family to set things up. if * the protocol is 0, the family is instructed to select an appropriate * default. */ sock = sock_alloc(); if (!sock) { if (net_ratelimit()) printk(KERN_WARNING "socket: no more sockets\n"); return -ENFILE; /* Not exactly a match, but its the closest posix thing */ } sock->type = type; #ifdef CONFIG_MODULES /* Attempt to load a protocol module if the find failed. * * 12/09/1996 Marcin: But! this makes REALLY only sense, if the user * requested real, full-featured networking support upon configuration. * Otherwise module support will break! */ if (net_families[family] == NULL) request_module("net-pf-%d", family); #endif rcu_read_lock(); pf = rcu_dereference(net_families[family]); err = -EAFNOSUPPORT; if (!pf) goto out_release; /* * We will call the ->create function, that possibly is in a loadable * module, so we have to bump that loadable module refcnt first. */ if (!try_module_get(pf->owner)) goto out_release; /* Now protected by module ref count */ rcu_read_unlock(); err = pf->create(net, sock, protocol); if (err < 0) goto out_module_put; /* * Now to bump the refcnt of the [loadable] module that owns this * socket at sock_release time we decrement its refcnt. */ if (!try_module_get(sock->ops->owner)) goto out_module_busy; /* * Now that we're done with the ->create function, the [loadable] * module can have its refcnt decremented */ module_put(pf->owner); err = security_socket_post_create(sock, family, type, protocol, kern); if (err) goto out_sock_release; *res = sock; return 0; out_module_busy: err = -EAFNOSUPPORT; out_module_put: sock->ops = NULL; module_put(pf->owner); out_sock_release: sock_release(sock); return err; out_release: rcu_read_unlock(); goto out_sock_release; } int sock_create(int family, int type, int protocol, struct socket **res) { return __sock_create(current->nsproxy->net_ns, family, type, protocol, res, 0); } |
1150~1171行做的很簡單，不過是參數檢查。
接下來的security_socket_create以及後面的security_socket_post_create都定義在/include/linux/security.h中定義的空函數
C
static inline int security_socket_create(int family, int type, int protocol, int kern) { return 0; } static inline int security_socket_post_create(struct socket *sock, int family, int type, int protocol, int kern) { return 0; }
1182行的sock_alloc的代碼如下：
C
480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 |
static struct socket *sock_alloc(void) { struct inode *inode; struct socket *sock; inode = new_inode(sock_mnt->mnt_sb); if (!inode) return NULL; sock = SOCKET_I(inode); kmemcheck_annotate_bitfield(sock, type); inode->i_mode = S_IFSOCK | S_IRWXUGO; inode->i_uid = current_fsuid(); inode->i_gid = current_fsgid(); percpu_add(sockets_in_use, 1); return sock; } |
其中的new_inode是在/fs/inode.c中定義
C
212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 |
static struct inode *alloc_inode(struct super_block *sb) { struct inode *inode; if (sb->s_op->alloc_inode) inode = sb->s_op->alloc_inode(sb); else inode = kmem_cache_alloc(inode_cachep, GFP_KERNEL); if (!inode) return NULL; if (unlikely(inode_init_always(sb, inode))) { if (inode->i_sb->s_op->destroy_inode) inode->i_sb->s_op->destroy_inode(inode); else kmem_cache_free(inode_cachep, inode); return NULL; } return inode; } |
C
659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 |
struct inode *new_inode(struct super_block *sb) { /* * On a 32bit, non LFS stat() call, glibc will generate an EOVERFLOW * error if st_ino won't fit in target struct field. Use 32bit counter * here to attempt to avoid that. */ static unsigned int last_ino; struct inode *inode; spin_lock_prefetch(&inode_lock); inode = alloc_inode(sb); if (inode) { spin_lock(&inode_lock); __inode_add_to_lists(sb, NULL, inode); inode->i_ino = ++last_ino; inode->i_state = 0; spin_unlock(&inode_lock); } return inode; } EXPORT_SYMBOL(new_inode); |
可以看出new_inode會調用alloc_inode分配inode，而alloc_inode會調用sockfs在VFS中註冊的相應的函數來處理，那這個函數是什麼呢？先來看一看/net/socket.c
C
241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 |
static struct inode *sock_alloc_inode(struct super_block *sb) { struct socket_alloc *ei; ei = kmem_cache_alloc(sock_inode_cachep, GFP_KERNEL); if (!ei) return NULL; init_waitqueue_head(&ei->socket.wait); ei->socket.fasync_list = NULL; ei->socket.state = SS_UNCONNECTED; ei->socket.flags = 0; ei->socket.ops = NULL; ei->socket.sk = NULL; ei->socket.file = NULL; return &ei->vfs_inode; } |
C
287 288 289 290 291 |
static const struct super_operations sockfs_ops = { .alloc_inode = sock_alloc_inode, .destroy_inode =sock_destroy_inode, .statfs = simple_statfs, }; |
爲幫助理解列出struct socket_alloc 結構體的定義。
C
794 795 796 797 798 799 800 801 802 |
struct socket_alloc { struct socket socket; struct inode vfs_inode; }; static inline struct socket *SOCKET_I(struct inode *inode) { return &container_of(inode, struct socket_alloc, vfs_inode)->socket; } |
可以看到這個函數其實就是sock_alloc_inode,該函數分配了一個struct socket_alloc類型的結構體，然後返回這個結構體中的一個成員變量vfs_inode的地址，可以看出來這就是一個inode結構。然後就回到了sock_alloc函數的第489行，通過SOCKET_I獲得與vfs_inode同在socket_alloc結構體中的成員socket的地址。然後程序返回到__sock_create的1190行。
1192開始的代碼說明，如果編譯內核開啓了CONFIG_MODULES也就是內核模塊的選項就先檢查內核現在是否有支持由family(就是domain)所指定的網域的代碼，如果沒有則通過request_module來安裝。
說到這裏就先看看1204行的net_families這個數組，很明顯它是控制和操作各個網域的一個控制結構體的集合，通過變量pf可以發現它的類型爲struct net_proto_family(/include/linux/net.h)
C
201 202 203 204 205 |
struct net_proto_family { int family; int (*create)(struct net *net, struct socket *sock, int protocol); struct module *owner; }; |
然後1219行通過pf調用相應網域的create的函數，可以很簡單地得出對於AF_UNIX, AF_INET, AF_INET6, AF_PACKET這些所對應的create函數肯定不一樣。接下來我們以AF_INET爲例說明。在/net/ipv4/af_inet.c中
C
934 935 936 937 938 |
static struct net_proto_family inet_family_ops = { .family = PF_INET, .create = inet_create, .owner = THIS_MODULE, }; |
由936可以得出對於AF_inet其create函數爲inet_create,定義於同一文件中。
C
265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 |
static int inet_create(struct net *net, struct socket *sock, int protocol) { struct sock *sk; struct inet_protosw *answer; struct inet_sock *inet; struct proto *answer_prot; unsigned char answer_flags; char answer_no_check; int try_loading_module = 0; int err; if (unlikely(!inet_ehash_secret)) if (sock->type != SOCK_RAW && sock->type != SOCK_DGRAM) build_ehash_secret(); sock->state = SS_UNCONNECTED; /* Look for the requested type/protocol pair. */ lookup_protocol: err = -ESOCKTNOSUPPORT; rcu_read_lock(); list_for_each_entry_rcu(answer, &inetsw[sock->type], list) { err = 0; /* Check the non-wild match. */ if (protocol == answer->protocol) { if (protocol != IPPROTO_IP) break; } else { /* Check for the two wild cases. */ if (IPPROTO_IP == protocol) { protocol = answer->protocol; break; } if (IPPROTO_IP == answer->protocol) break; } err = -EPROTONOSUPPORT; } if (unlikely(err)) { if (try_loading_module < 2) { rcu_read_unlock(); /* * Be more specific, e.g. net-pf-2-proto-132-type-1 * (net-pf-PF_INET-proto-IPPROTO_SCTP-type-SOCK_STREAM) */ if (++try_loading_module == 1) request_module("net-pf-%d-proto-%d-type-%d", PF_INET, protocol, sock->type); /* * Fall back to generic, e.g. net-pf-2-proto-132 * (net-pf-PF_INET-proto-IPPROTO_SCTP) */ else request_module("net-pf-%d-proto-%d", PF_INET, protocol); goto lookup_protocol; } else goto out_rcu_unlock; } err = -EPERM; if (answer->capability > 0 && !capable(answer->capability)) goto out_rcu_unlock; err = -EAFNOSUPPORT; if (!inet_netns_ok(net, protocol)) goto out_rcu_unlock; sock->ops = answer->ops; answer_prot = answer->prot; answer_no_check = answer->no_check; answer_flags = answer->flags; rcu_read_unlock(); WARN_ON(answer_prot->slab == NULL); err = -ENOBUFS; sk = sk_alloc(net, PF_INET, GFP_KERNEL, answer_prot); if (sk == NULL) goto out; err = 0; sk->sk_no_check = answer_no_check; if (INET_PROTOSW_REUSE & answer_flags) sk->sk_reuse = 1; inet = inet_sk(sk); inet->is_icsk = (INET_PROTOSW_ICSK & answer_flags) != 0; if (SOCK_RAW == sock->type) { inet->num = protocol; if (IPPROTO_RAW == protocol) inet->hdrincl = 1; } if (ipv4_config.no_pmtu_disc) inet->pmtudisc = IP_PMTUDISC_DONT; else inet->pmtudisc = IP_PMTUDISC_WANT; inet->id = 0; sock_init_data(sock, sk); sk->sk_destruct = inet_sock_destruct; sk->sk_protocol = protocol; sk->sk_backlog_rcv = sk->sk_prot->backlog_rcv; inet->uc_ttl = -1; inet->mc_loop = 1; inet->mc_ttl = 1; inet->mc_all = 1; inet->mc_index = 0; inet->mc_list = NULL; sk_refcnt_debug_inc(sk); if (inet->num) { /* It assumes that any protocol which allows * the user to assign a number at socket * creation time automatically * shares. */ inet->sport = htons(inet->num); /* Add to protocol hash chains. */ sk->sk_prot->hash(sk); } if (sk->sk_prot->init) { err = sk->sk_prot->init(sk); if (err) sk_common_release(sk); } out: return err; out_rcu_unlock: rcu_read_unlock(); goto out; } |
每283到325就是通過type和protocol從inetsw中找出對應的struct inet_protosw的結構體。inetsw是定義於(net/ipv4/af_inet.c)中定義的
C
120 121 122 123 124 |
/* The inetsw table contains everything that inet_create needs to * build a new socket. */ static struct list_head inetsw[SOCK_MAX]; static DEFINE_SPINLOCK(inetsw_lock); |
而對於struct inet_protosw是在/include/net/protocol.h中定義
C
75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 |
/* This is used to register socket interfaces for IP protocols. */ struct inet_protosw { struct list_head list; /* These two fields form the lookup key. */ unsigned short type; /* This is the 2nd argument to socket(2). */ unsigned short protocol; /* This is the L4 protocol number. */ struct proto *prot; const struct proto_ops *ops; int capability; /* Which (if any) capability do * we need to use this socket * interface? */ char no_check; /* checksum on rcv/xmit/none? */ unsigned char flags; /* See INET_PROTOSW_* below. */ }; |
inetsw其實是就是Linux內核的典型的組織鏈表結構的一個數組，是按type組織的。inetsw是通過inet_register_protosw初始化的
C
980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 |
void inet_register_protosw(struct inet_protosw *p) { struct list_head *lh; struct inet_protosw *answer; int protocol = p->protocol; struct list_head *last_perm; spin_lock_bh(&inetsw_lock); if (p->type >= SOCK_MAX) goto out_illegal; /* If we are trying to override a permanent protocol, bail. */ answer = NULL; last_perm = &inetsw[p->type]; list_for_each(lh, &inetsw[p->type]) { answer = list_entry(lh, struct inet_protosw, list); /* Check only the non-wild match. */ if (INET_PROTOSW_PERMANENT & answer->flags) { if (protocol == answer->protocol) break; last_perm = lh; } answer = NULL; } if (answer) goto out_permanent; /* Add the new entry after the last permanent entry if any, so that * the new entry does not override a permanent entry when matched with * a wild-card protocol. But it is allowed to override any existing * non-permanent entry. This means that when we remove this entry, the * system automatically returns to the old behavior. */ list_add_rcu(&p->list, last_perm); out: spin_unlock_bh(&inetsw_lock); return; out_permanent: printk(KERN_ERR "Attempt to override permanent protocol %d.\n", protocol); goto out; out_illegal: printk(KERN_ERR "Ignoring attempt to register invalid socket type %d.\n", p->type); goto out; } EXPORT_SYMBOL(inet_register_protosw); |
對於inet_register_protosw的調用是在inet_init中的第1593行進行的。
C
1542 1543 1544 1545 1546 1547 1548 1549 1550 1551 1552 1553 1554 1555 1556 1557 1558 1559 1560 1561 1562 1563 1564 1565 1566 1567 1568 1569 1570 1571 1572 1573 1574 1575 1576 1577 1578 1579 1580 1581 1582 1583 1584 1585 1586 1587 1588 1589 1590 1591 1592 1593 1594 1595 1596 1597 1598 1599 1600 1601 1602 1603 1604 1605 1606 1607 1608 1609 1610 1611 1612 1613 1614 1615 1616 1617 1618 1619 1620 1621 1622 1623 1624 1625 1626 1627 1628 1629 1630 1631 1632 1633 1634 1635 1636 1637 1638 1639 1640 1641 1642 1643 1644 1645 1646 1647 1648 1649 1650 1651 1652 1653 1654 1655 |
static int __init inet_init(void) { struct sk_buff *dummy_skb; struct inet_protosw *q; struct list_head *r; int rc = -EINVAL; BUILD_BUG_ON(sizeof(struct inet_skb_parm) > sizeof(dummy_skb->cb)); rc = proto_register(&tcp_prot, 1); if (rc) goto out; rc = proto_register(&udp_prot, 1); if (rc) goto out_unregister_tcp_proto; rc = proto_register(&raw_prot, 1); if (rc) goto out_unregister_udp_proto; /* * Tell SOCKET that we are alive... */ (void)sock_register(&inet_family_ops); #ifdef CONFIG_SYSCTL ip_static_sysctl_init(); #endif /* * Add all the base protocols. */ if (inet_add_protocol(&icmp_protocol, IPPROTO_ICMP) < 0) printk(KERN_CRIT "inet_init: Cannot add ICMP protocol\n"); if (inet_add_protocol(&udp_protocol, IPPROTO_UDP) < 0) printk(KERN_CRIT "inet_init: Cannot add UDP protocol\n"); if (inet_add_protocol(&tcp_protocol, IPPROTO_TCP) < 0) printk(KERN_CRIT "inet_init: Cannot add TCP protocol\n"); #ifdef CONFIG_IP_MULTICAST if (inet_add_protocol(&igmp_protocol, IPPROTO_IGMP) < 0) printk(KERN_CRIT "inet_init: Cannot add IGMP protocol\n"); #endif /* Register the socket-side information for inet_create. */ for (r = &inetsw[0]; r < &inetsw[SOCK_MAX]; ++r) INIT_LIST_HEAD(r); for (q = inetsw_array; q < &inetsw_array[INETSW_ARRAY_LEN]; ++q) inet_register_protosw(q); /* * Set the ARP module up */ arp_init(); /* * Set the IP module up */ ip_init(); tcp_v4_init(); /* Setup TCP slab cache for open requests. */ tcp_init(); /* Setup UDP memory threshold */ udp_init(); /* Add UDP-Lite (RFC 3828) */ udplite4_register(); /* * Set the ICMP layer up */ if (icmp_init() < 0) panic("Failed to create the ICMP control socket.\n"); /* * Initialise the multicast router */ #if defined(CONFIG_IP_MROUTE) if (ip_mr_init()) printk(KERN_CRIT "inet_init: Cannot init ipv4 mroute\n"); #endif /* * Initialise per-cpu ipv4 mibs */ if (init_ipv4_mibs()) printk(KERN_CRIT "inet_init: Cannot init ipv4 mibs\n"); ipv4_proc_init(); ipfrag_init(); dev_add_pack(&ip_packet_type); rc = 0; out: return rc; out_unregister_udp_proto: proto_unregister(&udp_prot); out_unregister_tcp_proto: proto_unregister(&tcp_prot); goto out; } fs_initcall(inet_init); |
從1592行可以看出初始化inetsw是用的inetsw_array數組，再看看inetsw_array數組。
C
852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 |
const struct proto_ops inet_stream_ops = { .family = PF_INET, .owner = THIS_MODULE, .release = inet_release, .bind = inet_bind, .connect = inet_stream_connect, .socketpair = sock_no_socketpair, .accept = inet_accept, .getname = inet_getname, .poll = tcp_poll, .ioctl = inet_ioctl, .listen = inet_listen, .shutdown = inet_shutdown, .setsockopt = sock_common_setsockopt, .getsockopt = sock_common_getsockopt, .sendmsg = tcp_sendmsg, .recvmsg = sock_common_recvmsg, .mmap = sock_no_mmap, .sendpage = tcp_sendpage, .splice_read = tcp_splice_read, #ifdef CONFIG_COMPAT .compat_setsockopt = compat_sock_common_setsockopt, .compat_getsockopt = compat_sock_common_getsockopt, #endif }; EXPORT_SYMBOL(inet_stream_ops); const struct proto_ops inet_dgram_ops = { .family = PF_INET, .owner = THIS_MODULE, .release = inet_release, .bind = inet_bind, .connect = inet_dgram_connect, .socketpair = sock_no_socketpair, .accept = sock_no_accept, .getname = inet_getname, .poll = udp_poll, .ioctl = inet_ioctl, .listen = sock_no_listen, .shutdown = inet_shutdown, .setsockopt = sock_common_setsockopt, .getsockopt = sock_common_getsockopt, .sendmsg = inet_sendmsg, .recvmsg = sock_common_recvmsg, .mmap = sock_no_mmap, .sendpage = inet_sendpage, #ifdef CONFIG_COMPAT .compat_setsockopt = compat_sock_common_setsockopt, .compat_getsockopt = compat_sock_common_getsockopt, #endif }; EXPORT_SYMBOL(inet_dgram_ops); /* * For SOCK_RAW sockets; should be the same as inet_dgram_ops but without * udp_poll */ static const struct proto_ops inet_sockraw_ops = { .family = PF_INET, .owner = THIS_MODULE, .release = inet_release, .bind = inet_bind, .connect = inet_dgram_connect, .socketpair = sock_no_socketpair, .accept = sock_no_accept, .getname = inet_getname, .poll = datagram_poll, .ioctl = inet_ioctl, .listen = sock_no_listen, .shutdown = inet_shutdown, .setsockopt = sock_common_setsockopt, .getsockopt = sock_common_getsockopt, .sendmsg = inet_sendmsg, .recvmsg = sock_common_recvmsg, .mmap = sock_no_mmap, .sendpage = inet_sendpage, #ifdef CONFIG_COMPAT .compat_setsockopt = compat_sock_common_setsockopt, .compat_getsockopt = compat_sock_common_getsockopt, #endif }; static struct net_proto_family inet_family_ops = { .family = PF_INET, .create = inet_create, .owner = THIS_MODULE, }; /* Upon startup we insert all the elements in inetsw_array[] into * the linked list inetsw. */ static struct inet_protosw inetsw_array[] = { { .type = SOCK_STREAM, .protocol = IPPROTO_TCP, .prot = &tcp_prot, .ops = &inet_stream_ops, .capability = -1, .no_check = 0, .flags = INET_PROTOSW_PERMANENT | INET_PROTOSW_ICSK, }, { .type = SOCK_DGRAM, .protocol = IPPROTO_UDP, .prot = &udp_prot, .ops = &inet_dgram_ops, .capability = -1, .no_check = UDP_CSUM_DEFAULT, .flags = INET_PROTOSW_PERMANENT, }, { .type = SOCK_RAW, .protocol = IPPROTO_IP, /* wild card */ .prot = &raw_prot, .ops = &inet_sockraw_ops, .capability = CAP_NET_RAW, .no_check = UDP_CSUM_DEFAULT, .flags = INET_PROTOSW_REUSE, } }; #define INETSW_ARRAY_LEN ARRAY_SIZE(inetsw_array) |
假設我們分析ipv4中的TCP協議，其它協議也可以參照分析。現在回到inet_create函數，這個函數最重要的一行就是335，這一行的作用就是初始化套接口socket所應該對應的操作函數。例如如果用socket(AF_INET, SOCK_STREAM, 0);創建套接字，則內核就會在這裏爲這個套接字關聯上相應的TCP的操作函數集inet_stream_ops，以後在這個套接字上的數據的各種操作如accept listen bind send recv都會通過這些函數完成。
接下來在inet_create中的344後就是分配一個struct sock結構體，這個sock結構和socket結構是一一對應的，兩個結構各有一個成員指向對方。struct sock是在include/net/sock.h中定義，它有兩個非常重要的成員sk_receive_queue和sk_write_queue。還有兩個成員sk_rcvbuf,sk_sndbuf分別代表接收和發送緩衝區的大小，默認是32767字節，是在sock_init_data(net/core/sock.c)中初始化的。另外對於有連接模式可能要求超時重傳，所以還有一個sk_timer的定時隊列。
C
144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 |
/** * struct sock - network layer representation of sockets * @__sk_common: shared layout with inet_timewait_sock * @sk_shutdown: mask of %SEND_SHUTDOWN and/or %RCV_SHUTDOWN * @sk_userlocks: %SO_SNDBUF and %SO_RCVBUF settings * @sk_lock: synchronizer * @sk_rcvbuf: size of receive buffer in bytes * @sk_sleep: sock wait queue * @sk_dst_cache: destination cache * @sk_dst_lock: destination cache lock * @sk_policy: flow policy * @sk_rmem_alloc: receive queue bytes committed * @sk_receive_queue: incoming packets * @sk_wmem_alloc: transmit queue bytes committed * @sk_write_queue: Packet sending queue * @sk_async_wait_queue: DMA copied packets * @sk_omem_alloc: "o" is "option" or "other" * @sk_wmem_queued: persistent queue size * @sk_forward_alloc: space allocated forward * @sk_allocation: allocation mode * @sk_sndbuf: size of send buffer in bytes * @sk_flags: %SO_LINGER (l_onoff), %SO_BROADCAST, %SO_KEEPALIVE, * %SO_OOBINLINE settings, %SO_TIMESTAMPING settings * @sk_no_check: %SO_NO_CHECK setting, wether or not checkup packets * @sk_route_caps: route capabilities (e.g. %NETIF_F_TSO) * @sk_gso_type: GSO type (e.g. %SKB_GSO_TCPV4) * @sk_gso_max_size: Maximum GSO segment size to build * @sk_lingertime: %SO_LINGER l_linger setting * @sk_backlog: always used with the per-socket spinlock held * @sk_callback_lock: used with the callbacks in the end of this struct * @sk_error_queue: rarely used * @sk_prot_creator: sk_prot of original sock creator (see ipv6_setsockopt, * IPV6_ADDRFORM for instance) * @sk_err: last error * @sk_err_soft: errors that don't cause failure but are the cause of a * persistent failure not just 'timed out' * @sk_drops: raw/udp drops counter * @sk_ack_backlog: current listen backlog * @sk_max_ack_backlog: listen backlog set in listen() * @sk_priority: %SO_PRIORITY setting * @sk_type: socket type (%SOCK_STREAM, etc) * @sk_protocol: which protocol this socket belongs in this network family * @sk_peercred: %SO_PEERCRED setting * @sk_rcvlowat: %SO_RCVLOWAT setting * @sk_rcvtimeo: %SO_RCVTIMEO setting * @sk_sndtimeo: %SO_SNDTIMEO setting * @sk_filter: socket filtering instructions * @sk_protinfo: private area, net family specific, when not using slab * @sk_timer: sock cleanup timer * @sk_stamp: time stamp of last packet received * @sk_socket: Identd and reporting IO signals * @sk_user_data: RPC layer private data * @sk_sndmsg_page: cached page for sendmsg * @sk_sndmsg_off: cached offset for sendmsg * @sk_send_head: front of stuff to transmit * @sk_security: used by security modules * @sk_mark: generic packet mark * @sk_write_pending: a write to stream socket waits to start * @sk_state_change: callback to indicate change in the state of the sock * @sk_data_ready: callback to indicate there is data to be processed * @sk_write_space: callback to indicate there is bf sending space available * @sk_error_report: callback to indicate errors (e.g. %MSG_ERRQUEUE) * @sk_backlog_rcv: callback to process the backlog * @sk_destruct: called at sock freeing time, i.e. when all refcnt == 0 */ struct sock { /* * Now struct inet_timewait_sock also uses sock_common, so please just * don't add nothing before this first member (__sk_common) --acme */ struct sock_common __sk_common; #define sk_node __sk_common.skc_node #define sk_nulls_node __sk_common.skc_nulls_node #define sk_refcnt __sk_common.skc_refcnt #define sk_copy_start __sk_common.skc_hash #define sk_hash __sk_common.skc_hash #define sk_family __sk_common.skc_family #define sk_state __sk_common.skc_state #define sk_reuse __sk_common.skc_reuse #define sk_bound_dev_if __sk_common.skc_bound_dev_if #define sk_bind_node __sk_common.skc_bind_node #define sk_prot __sk_common.skc_prot #define sk_net __sk_common.skc_net kmemcheck_bitfield_begin(flags); unsigned int sk_shutdown : 2, sk_no_check : 2, sk_userlocks : 4, sk_protocol : 8, sk_type : 16; kmemcheck_bitfield_end(flags); int sk_rcvbuf; socket_lock_t sk_lock; /* * The backlog queue is special, it is always used with * the per-socket spinlock held and requires low latency * access. Therefore we special case it's implementation. */ struct { struct sk_buff *head; struct sk_buff *tail; } sk_backlog; wait_queue_head_t *sk_sleep; struct dst_entry *sk_dst_cache; #ifdef CONFIG_XFRM struct xfrm_policy *sk_policy[2]; #endif rwlock_t sk_dst_lock; atomic_t sk_rmem_alloc; atomic_t sk_wmem_alloc; atomic_t sk_omem_alloc; int sk_sndbuf; struct sk_buff_head sk_receive_queue; struct sk_buff_head sk_write_queue; #ifdef CONFIG_NET_DMA struct sk_buff_head sk_async_wait_queue; #endif int sk_wmem_queued; int sk_forward_alloc; gfp_t sk_allocation; int sk_route_caps; int sk_gso_type; unsigned int sk_gso_max_size; int sk_rcvlowat; unsigned long sk_flags; unsigned long sk_lingertime; struct sk_buff_head sk_error_queue; struct proto *sk_prot_creator; rwlock_t sk_callback_lock; int sk_err, sk_err_soft; atomic_t sk_drops; unsigned short sk_ack_backlog; unsigned short sk_max_ack_backlog; __u32 sk_priority; struct ucred sk_peercred; long sk_rcvtimeo; long sk_sndtimeo; struct sk_filter *sk_filter; void *sk_protinfo; struct timer_list sk_timer; ktime_t sk_stamp; struct socket *sk_socket; void *sk_user_data; struct page *sk_sndmsg_page; struct sk_buff *sk_send_head; __u32 sk_sndmsg_off; int sk_write_pending; #ifdef CONFIG_SECURITY void *sk_security; #endif __u32 sk_mark; /* XXX 4 bytes hole on 64 bit */ void (*sk_state_change)(struct sock *sk); void (*sk_data_ready)(struct sock *sk, int bytes); void (*sk_write_space)(struct sock *sk); void (*sk_error_report)(struct sock *sk); int (*sk_backlog_rcv)(struct sock *sk, struct sk_buff *skb); void (*sk_destruct)(struct sock *sk); }; |
在分析sk_alloc之前先分析一下answer_prot. answer_prot是struct proto類型(include/net/sock.h)
C
606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 |
/* Networking protocol blocks we attach to sockets. * socket layer -> transport layer interface * transport -> network interface is defined by struct inet_proto */ struct proto { void (*close)(struct sock *sk, long timeout); int (*connect)(struct sock *sk, struct sockaddr *uaddr, int addr_len); int (*disconnect)(struct sock *sk, int flags); struct sock * (*accept) (struct sock *sk, int flags, int *err); int (*ioctl)(struct sock *sk, int cmd, unsigned long arg); int (*init)(struct sock *sk); void (*destroy)(struct sock *sk); void (*shutdown)(struct sock *sk, int how); int (*setsockopt)(struct sock *sk, int level, int optname, char __user *optval, unsigned int optlen); int (*getsockopt)(struct sock *sk, int level, int optname, char __user *optval, int __user *option); #ifdef CONFIG_COMPAT int (*compat_setsockopt)(struct sock *sk, int level, int optname, char __user *optval, unsigned int optlen); int (*compat_getsockopt)(struct sock *sk, int level, int optname, char __user *optval, int __user *option); #endif int (*sendmsg)(struct kiocb *iocb, struct sock *sk, struct msghdr *msg, size_t len); int (*recvmsg)(struct kiocb *iocb, struct sock *sk, struct msghdr *msg, size_t len, int noblock, int flags, int *addr_len); int (*sendpage)(struct sock *sk, struct page *page, int offset, size_t size, int flags); int (*bind)(struct sock *sk, struct sockaddr *uaddr, int addr_len); int (*backlog_rcv) (struct sock *sk, struct sk_buff *skb); /* Keeping track of sk's, looking them up, and port selection methods. */ void (*hash)(struct sock *sk); void (*unhash)(struct sock *sk); int (*get_port)(struct sock *sk, unsigned short snum); /* Keeping track of sockets in use */ #ifdef CONFIG_PROC_FS unsigned int inuse_idx; #endif /* Memory pressure */ void (*enter_memory_pressure)(struct sock *sk); atomic_t *memory_allocated; /* Current allocated memory. */ struct percpu_counter *sockets_allocated; /* Current number of sockets. */ /* * Pressure flag: try to collapse. * Technical note: it is used by multiple contexts non atomically. * All the __sk_mem_schedule() is of this nature: accounting * is strict, actions are advisory and have some latency. */ int *memory_pressure; int *sysctl_mem; int *sysctl_wmem; int *sysctl_rmem; int max_header; struct kmem_cache *slab; unsigned int obj_size; int slab_flags; struct percpu_counter *orphan_count; struct request_sock_ops *rsk_prot; struct timewait_sock_ops *twsk_prot; union { struct inet_hashinfo *hashinfo; struct udp_table *udp_table; struct raw_hashinfo *raw_hash; } h; struct module *owner; char name[32]; struct list_head node; #ifdef SOCK_REFCNT_DEBUG atomic_t socks; #endif }; |
假設分析的是TCP協議，則通過336行的賦值從inetsw_array找到其prot成員變量爲tcp_prot(net/ipv4/tcp_ipv4.h)。
C
2418 2419 2420 2421 2422 2423 2424 2425 2426 2427 2428 2429 2430 2431 2432 2433 2434 2435 2436 2437 2438 2439 2440 2441 2442 2443 2444 2445 2446 2447 2448 2449 2450 2451 2452 2453 2454 |
struct proto tcp_prot = { .name = "TCP", .owner = THIS_MODULE, .close = tcp_close, .connect = tcp_v4_connect, .disconnect = tcp_disconnect, .accept = inet_csk_accept, .ioctl = tcp_ioctl, .init = tcp_v4_init_sock, .destroy = tcp_v4_destroy_sock, .shutdown = tcp_shutdown, .setsockopt = tcp_setsockopt, .getsockopt = tcp_getsockopt, .recvmsg = tcp_recvmsg, .backlog_rcv = tcp_v4_do_rcv, .hash = inet_hash, .unhash = inet_unhash, .get_port = inet_csk_get_port, .enter_memory_pressure = tcp_enter_memory_pressure, .sockets_allocated = &tcp_sockets_allocated, .orphan_count = &tcp_orphan_count, .memory_allocated = &tcp_memory_allocated, .memory_pressure = &tcp_memory_pressure, .sysctl_mem = sysctl_tcp_mem, .sysctl_wmem = sysctl_tcp_wmem, .sysctl_rmem = sysctl_tcp_rmem, .max_header = MAX_TCP_HEADER, .obj_size = sizeof(struct tcp_sock), .slab_flags = SLAB_DESTROY_BY_RCU, .twsk_prot = &tcp_timewait_sock_ops, .rsk_prot = &tcp_request_sock_ops, .h.hashinfo = &tcp_hashinfo, #ifdef CONFIG_COMPAT .compat_setsockopt = compat_tcp_setsockopt, .compat_getsockopt = compat_tcp_getsockopt, #endif }; |
通過tcp_prot的結構體對各成員的賦值可以發現並沒有初始化，而obj_size被初始化爲sizeof(struct tcp_sock)這一點可以在後面的分析中看到。接下來看inet_create的344行，即sk_alloc(net/ipv4/af_inet.c)。
C
951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 |
static struct sock *sk_prot_alloc(struct proto *prot, gfp_t priority, int family) { struct sock *sk; struct kmem_cache *slab; slab = prot->slab; if (slab != NULL) { sk = kmem_cache_alloc(slab, priority & ~__GFP_ZERO); if (!sk) return sk; if (priority & __GFP_ZERO) { /* * caches using SLAB_DESTROY_BY_RCU should let * sk_node.next un-modified. Special care is taken * when initializing object to zero. */ if (offsetof(struct sock, sk_node.next) != 0) memset(sk, 0, offsetof(struct sock, sk_node.next)); memset(&sk->sk_node.pprev, 0, prot->obj_size - offsetof(struct sock, sk_node.pprev)); } } else sk = kmalloc(prot->obj_size, priority); if (sk != NULL) { kmemcheck_annotate_bitfield(sk, flags); if (security_sk_alloc(sk, family, priority)) goto out_free; if (!try_module_get(prot->owner)) goto out_free_sec; } return sk; out_free_sec: security_sk_free(sk); out_free: if (slab != NULL) kmem_cache_free(slab, sk); else kfree(sk); return NULL; } |
C
1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 |
/** * sk_alloc - All socket objects are allocated here * @net: the applicable net namespace * @family: protocol family * @priority: for allocation (%GFP_KERNEL, %GFP_ATOMIC, etc) * @prot: struct proto associated with this new sock instance */ struct sock *sk_alloc(struct net *net, int family, gfp_t priority, struct proto *prot) { struct sock *sk; sk = sk_prot_alloc(prot, priority | __GFP_ZERO, family); if (sk) { sk->sk_family = family; /* * See comment in struct sock definition to understand * why we need sk_prot_creator -acme */ sk->sk_prot = sk->sk_prot_creator = prot; sock_lock_init(sk); sock_net_set(sk, get_net(net)); atomic_set(&sk->sk_wmem_alloc, 1); } return sk; } EXPORT_SYMBOL(sk_alloc); |
很明顯在sk_alloc中直接調用sk_prot_alloc來分配sock結構，在sk_prot_alloc中先判定slab是否爲空(如前提示)，由於tcp_prot並未初始化slab所以直接分配obj_size大小即sizeof(struct tcp_sock)的空間，並返回空間類型爲struct sock *的地址，但是又可以看到該空間的大小爲sizeof(struct tcp_sock)，那就說明有兩種情況：一、sizeof(struct tcp_sock) == sizeof(struct sock)
二、sizeof(struct tcp_sock) >= sizeof(struct sock) 。通過分析實際是第二種情況，通過列出一系列數據結構可以很明顯地看出。
先來看struct tcp_sock結構的定義(include/linux/tcp.h)
C
247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 |
struct tcp_sock { /* inet_connection_sock has to be the first member of tcp_sock */ struct inet_connection_sock inet_conn; u16 tcp_header_len; /* Bytes of tcp header to send */ u16 xmit_size_goal_segs; /* Goal for segmenting output packets */ /* * Header prediction flags * 0x5?10 << 16 + snd_wnd in net byte order */ __be32 pred_flags; /* * RFC793 variables by their proper names. This means you can * read the code and the spec side by side (and laugh ...) * See RFC793 and RFC1122. The RFC writes these in capitals. */ u32 rcv_nxt; /* What we want to receive next */ u32 copied_seq; /* Head of yet unread data */ u32 rcv_wup; /* rcv_nxt on last window update sent */ u32 snd_nxt; /* Next sequence we send */ u32 snd_una; /* First byte we want an ack for */ u32 snd_sml; /* Last byte of the most recently transmitted small packet */ u32 rcv_tstamp; /* timestamp of last received ACK (for keepalives) */ u32 lsndtime; /* timestamp of last sent data packet (for restart window) */ /* Data for direct copy to user */ struct { struct sk_buff_head prequeue; struct task_struct *task; struct iovec *iov; int memory; int len; #ifdef CONFIG_NET_DMA /* members for async copy */ struct dma_chan *dma_chan; int wakeup; struct dma_pinned_list *pinned_list; dma_cookie_t dma_cookie; #endif } ucopy; u32 snd_wl1; /* Sequence for window update */ u32 snd_wnd; /* The window we expect to receive */ u32 max_window; /* Maximal window ever seen from peer */ u32 mss_cache; /* Cached effective mss, not including SACKS */ u32 window_clamp; /* Maximal window to advertise */ u32 rcv_ssthresh; /* Current window clamp */ u32 frto_highmark; /* snd_nxt when RTO occurred */ u16 advmss; /* Advertised MSS */ u8 frto_counter; /* Number of new acks after RTO */ u8 nonagle; /* Disable Nagle algorithm? */ /* RTT measurement */ u32 srtt; /* smoothed round trip time << 3 */ u32 mdev; /* medium deviation */ u32 mdev_max; /* maximal mdev for the last rtt period */ u32 rttvar; /* smoothed mdev_max */ u32 rtt_seq; /* sequence number to update rttvar */ u32 packets_out; /* Packets which are "in flight" */ u32 retrans_out; /* Retransmitted packets out */ u16 urg_data; /* Saved octet of OOB data and control flags */ u8 ecn_flags; /* ECN status bits. */ u8 reordering; /* Packet reordering metric. */ u32 snd_up; /* Urgent pointer */ u8 keepalive_probes; /* num of allowed keep alive probes */ /* * Options received (usually on last packet, some only on SYN packets). */ struct tcp_options_received rx_opt; /* * Slow start and congestion control (see also Nagle, and Karn & Partridge) */ u32 snd_ssthresh; /* Slow start size threshold */ u32 snd_cwnd; /* Sending congestion window */ u32 snd_cwnd_cnt; /* Linear increase counter */ u32 snd_cwnd_clamp; /* Do not allow snd_cwnd to grow above this */ u32 snd_cwnd_used; u32 snd_cwnd_stamp; u32 rcv_wnd; /* Current receiver window */ u32 write_seq; /* Tail(+1) of data held in tcp send buffer */ u32 pushed_seq; /* Last pushed seq, required to talk to windows */ u32 lost_out; /* Lost packets */ u32 sacked_out; /* SACK'd packets */ u32 fackets_out; /* FACK'd packets */ u32 tso_deferred; u32 bytes_acked; /* Appropriate Byte Counting - RFC3465 */ /* from STCP, retrans queue hinting */ struct sk_buff* lost_skb_hint; struct sk_buff *scoreboard_skb_hint; struct sk_buff *retransmit_skb_hint; struct sk_buff_head out_of_order_queue; /* Out of order segments go here */ /* SACKs data, these 2 need to be together (see tcp_build_and_update_options) */ struct tcp_sack_block duplicate_sack[1]; /* D-SACK block */ struct tcp_sack_block selective_acks[4]; /* The SACKS themselves*/ struct tcp_sack_block recv_sack_cache[4]; struct sk_buff *highest_sack; /* highest skb with SACK received * (validity guaranteed only if * sacked_out > 0) */ int lost_cnt_hint; u32 retransmit_high; /* L-bits may be on up to this seqno */ u32 lost_retrans_low; /* Sent seq after any rxmit (lowest) */ u32 prior_ssthresh; /* ssthresh saved at recovery start */ u32 high_seq; /* snd_nxt at onset of congestion */ u32 retrans_stamp; /* Timestamp of the last retransmit, * also used in SYN-SENT to remember stamp of * the first SYN. */ u32 undo_marker; /* tracking retrans started here. */ int undo_retrans; /* number of undoable retransmissions. */ u32 total_retrans; /* Total retransmits for entire connection */ u32 urg_seq; /* Seq of received urgent pointer */ unsigned int keepalive_time; /* time before keep alive takes place */ unsigned int keepalive_intvl; /* time interval between keep alive probes */ int linger2; /* Receiver side RTT estimation */ struct { u32 rtt; u32 seq; u32 time; } rcv_rtt_est; /* Receiver queue space */ struct { int space; u32 seq; u32 time; } rcvq_space; /* TCP-specific MTU probe information. */ struct { u32 probe_seq_start; u32 probe_seq_end; } mtu_probe; #ifdef CONFIG_TCP_MD5SIG /* TCP AF-Specific parts; only used by MD5 Signature support so far */ const struct tcp_sock_af_ops *af_specific; /* TCP MD5 Signature Option information */ struct tcp_md5sig_info *md5sig_info; #endif }; |
在tcp_sock的結構體的第一個成員變量類型爲struct inet_connection_sock(include/net/inet_connection_sock.h)
C
67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 |
/** inet_connection_sock - INET connection oriented sock * * @icsk_accept_queue: FIFO of established children * @icsk_bind_hash: Bind node * @icsk_timeout: Timeout * @icsk_retransmit_timer: Resend (no ack) * @icsk_rto: Retransmit timeout * @icsk_pmtu_cookie Last pmtu seen by socket * @icsk_ca_ops Pluggable congestion control hook * @icsk_af_ops Operations which are AF_INET{4,6} specific * @icsk_ca_state: Congestion control state * @icsk_retransmits: Number of unrecovered [RTO] timeouts * @icsk_pending: Scheduled timer event * @icsk_backoff: Backoff * @icsk_syn_retries: Number of allowed SYN (or equivalent) retries * @icsk_probes_out: unanswered 0 window probes * @icsk_ext_hdr_len: Network protocol overhead (IP/IPv6 options) * @icsk_ack: Delayed ACK control data * @icsk_mtup; MTU probing control data */ struct inet_connection_sock { /* inet_sock has to be the first member! */ struct inet_sock icsk_inet; struct request_sock_queue icsk_accept_queue; struct inet_bind_bucket *icsk_bind_hash; unsigned long icsk_timeout; struct timer_list icsk_retransmit_timer; struct timer_list icsk_delack_timer; __u32 icsk_rto; __u32 icsk_pmtu_cookie; const struct tcp_congestion_ops *icsk_ca_ops; const struct inet_connection_sock_af_ops *icsk_af_ops; unsigned int (*icsk_sync_mss)(struct sock *sk, u32 pmtu); __u8 icsk_ca_state; __u8 icsk_retransmits; __u8 icsk_pending; __u8 icsk_backoff; __u8 icsk_syn_retries; __u8 icsk_probes_out; __u16 icsk_ext_hdr_len; struct { __u8 pending; /* ACK is pending */ __u8 quick; /* Scheduled number of quick acks */ __u8 pingpong; /* The session is interactive */ __u8 blocked; /* Delayed ACK was blocked by socket lock */ __u32 ato; /* Predicted tick of soft clock */ unsigned long timeout; /* Currently scheduled timeout */ __u32 lrcvtime; /* timestamp of last received data packet */ __u16 last_seg_size; /* Size of last incoming segment */ __u16 rcv_mss; /* MSS used for delayed ACK decisions */ } icsk_ack; struct { int enabled; /* Range of MTUs to search */ int search_high; int search_low; /* Information on the current probe. */ int probe_size; } icsk_mtup; u32 icsk_ca_priv[16]; #define ICSK_CA_PRIV_SIZE (16 * sizeof(u32)) }; |
在 inet_connection_sock結構體中第一個成員變量類型爲struct inet_sock(include/net/inet_sock.h)
C
92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 |
/** struct inet_sock - representation of INET sockets * * @sk - ancestor class * @pinet6 - pointer to IPv6 control block * @daddr - Foreign IPv4 addr * @rcv_saddr - Bound local IPv4 addr * @dport - Destination port * @num - Local port * @saddr - Sending source * @uc_ttl - Unicast TTL * @sport - Source port * @id - ID counter for DF pkts * @tos - TOS * @mc_ttl - Multicasting TTL * @is_icsk - is this an inet_connection_sock? * @mc_index - Multicast device index * @mc_list - Group array * @cork - info to build ip hdr on each ip frag while socket is corked */ struct inet_sock { /* sk and pinet6 has to be the first two members of inet_sock */ struct sock sk; #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE) struct ipv6_pinfo *pinet6; #endif /* Socket demultiplex comparisons on incoming packets. */ __be32 daddr; __be32 rcv_saddr; __be16 dport; __u16 num; __be32 saddr; __s16 uc_ttl; __u16 cmsg_flags; struct ip_options *opt; __be16 sport; __u16 id; __u8 tos; __u8 mc_ttl; __u8 pmtudisc; __u8 recverr:1, is_icsk:1, freebind:1, hdrincl:1, mc_loop:1, transparent:1, mc_all:1; int mc_index; __be32 mc_addr; struct ip_mc_socklist *mc_list; struct { unsigned int flags; unsigned int fragsize; struct ip_options *opt; struct dst_entry *dst; int length; /* Total length of all frames */ __be32 addr; struct flowi fl; } cork; }; |
而inet_sock的第一個成員正是struct sock類型，所以sk_prot_alloc直接返回struct sock *類型指針是沒有問題的，接下來執行inet_create中的353行用inet_sk通過sk獲得inet指針的值，inet_sk函數其實就相當於強制類型轉換，返回的就是sk的指針。
接下來程序就一路返回到__sock_create，接着再返回到sys_socket中。在sys_socket中調用了最後一個函數sock_map_fd(net/socket.c，將socket指針sock與一個已經打開的文件號關聯起來返回給用戶程序。
C
335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 |
/* * Obtains the first available file descriptor and sets it up for use. * * These functions create file structures and maps them to fd space * of the current process. On success it returns file descriptor * and file struct implicitly stored in sock->file. * Note that another thread may close file descriptor before we return * from this function. We use the fact that now we do not refer * to socket after mapping. If one day we will need it, this * function will increment ref. count on file by 1. * * In any case returned fd MAY BE not valid! * This race condition is unavoidable * with shared fd spaces, we cannot solve it inside kernel, * but we take care of internal coherence yet. */ static int sock_alloc_fd(struct file **filep, int flags) { int fd; fd = get_unused_fd_flags(flags); if (likely(fd >= 0)) { struct file *file = get_empty_filp(); *filep = file; if (unlikely(!file)) { put_unused_fd(fd); return -ENFILE; } } else *filep = NULL; return fd; } static int sock_attach_fd(struct socket *sock, struct file *file, int flags) { struct dentry *dentry; struct qstr name = { .name = "" }; dentry = d_alloc(sock_mnt->mnt_sb->s_root, &name); if (unlikely(!dentry)) return -ENOMEM; dentry->d_op = &sockfs_dentry_operations; /* * We dont want to push this dentry into global dentry hash table. * We pretend dentry is already hashed, by unsetting DCACHE_UNHASHED * This permits a working /proc/$pid/fd/XXX on sockets */ dentry->d_flags &= ~DCACHE_UNHASHED; d_instantiate(dentry, SOCK_INODE(sock)); sock->file = file; init_file(file, sock_mnt, dentry, FMODE_READ | FMODE_WRITE, &socket_file_ops); SOCK_INODE(sock)->i_fop = &socket_file_ops; file->f_flags = O_RDWR | (flags & O_NONBLOCK); file->f_pos = 0; file->private_data = sock; return 0; } int sock_map_fd(struct socket *sock, int flags) { struct file *newfile; int fd = sock_alloc_fd(&newfile, flags); if (likely(fd >= 0)) { int err = sock_attach_fd(sock, newfile, flags); if (unlikely(err < 0)) { put_filp(newfile); put_unused_fd(fd); return err; } fd_install(fd, newfile); } return fd; } |
fs/dcache.c
C
982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 |
/* the caller must hold dcache_lock */ static void __d_instantiate(struct dentry *dentry, struct inode *inode) { if (inode) list_add(&dentry->d_alias, &inode->i_dentry); dentry->d_inode = inode; fsnotify_d_instantiate(dentry, inode); } /** * d_instantiate - fill in inode information for a dentry * @entry: dentry to complete * @inode: inode to attach to this dentry * * Fill in inode information in the entry. * * This turns negative dentries into productive full members * of society. * * NOTE! This assumes that the inode count has been incremented * (or otherwise set) by the caller to indicate that it is now * in use by the dcache. */ void d_instantiate(struct dentry *entry, struct inode * inode) { BUG_ON(!list_empty(&entry->d_alias)); spin_lock(&dcache_lock); __d_instantiate(entry, inode); spin_unlock(&dcache_lock); security_d_instantiate(entry, inode); } |
/net/socket.c
C
122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 |
/* * Socket files have a set of 'special' operations as well as the generic file ones. These don't appear * in the operation structures but are done directly via the socketcall() multiplexor. */ static const struct file_operations socket_file_ops = { .owner = THIS_MODULE, .llseek = no_llseek, .aio_read = sock_aio_read, .aio_write = sock_aio_write, .poll = sock_poll, .unlocked_ioctl = sock_ioctl, #ifdef CONFIG_COMPAT .compat_ioctl = compat_sock_ioctl, #endif .mmap = sock_mmap, .open = sock_no_open, /* special open code to disallow open via /proc */ .release = sock_close, .fasync = sock_fasync, .sendpage = sock_sendpage, .splice_write = generic_splice_sendpage, .splice_read = sock_splice_read, }; |
在sock_map_fd中先通過402行獲得一個未用的已經打開的文件號以及file結構，然後通過405行調用sock_attach_fd將文件號與sock相關聯起來，在sock_attach_fd中先通地375行從sockfs中分配一個dentry，其中sock_mnt就是在描述sockfs中提到的，d_instantiate的作用就是將dentry與socket的inode關聯起來，然後388行又將sock->file與file關聯起來。389～390行將socket文件上的操作初始化爲socket_file_ops。這樣，通過send/recv進入內核將調用inet_stream_ops中的函數，而通過read/write調用將調用socket_file_ops中的函數。然後反回至sys_socket函數中，再經過系統調用切換到用戶態，socket函數的整個調用過程完成。
轉自http://acm.hrbeu.edu.cn/~puppy/2011/02/28/linux-%E5%8D%8F%E8%AE%AE%E6%A0%88%E5%88%86%E6%9E%90-socket/