[UNIX]: EOF on non-blocking SOCK_SEQPACKET
I am not absolutely sure whether this actually is a bug (as in: I've got
no clue what the standards say or what other implementations do), but at
least I was pretty surprised when I noticed that a recv() on a
non-blocking unix domain socket of type SOCK_SEQPACKET (which is connection
oriented, after all) where the remote end has closed the connection
returned -1 (EAGAIN) rather than 0 to indicate end of file.
This is a test case:
| #include <sys/types.h>
| #include <unistd.h>
| #include <sys/socket.h>
| #include <sys/un.h>
| #include <fcntl.h>
| #include <string.h>
| #include <stdlib.h>
|
| int main(){
| int sock;
| struct sockaddr_un addr;
| char buf[4096];
| int pfds[2];
|
| pipe(pfds);
| sock=socket(PF_UNIX,SOCK_SEQPACKET,0);
| addr.sun_family=AF_UNIX;
| strcpy(addr.sun_path,"/tmp/foobar_testsock");
| bind(sock,(struct sockaddr *)&addr,sizeof(addr));
| listen(sock,1);
| if(fork()){
| close(sock);
| sock=socket(PF_UNIX,SOCK_SEQPACKET,0);
| connect(sock,(struct sockaddr *)&addr,sizeof(addr));
| fcntl(sock,F_SETFL,fcntl(sock,F_GETFL)|O_NONBLOCK);
| close(pfds[1]);
| read(pfds[0],buf,sizeof(buf));
| recv(sock,buf,sizeof(buf),0); // <-- this one
| }else accept(sock,NULL,NULL);
| exit(0);
| }
If you try it, make sure /tmp/foobar_testsock doesn't exist.
The marked recv() returns -1 (EAGAIN) on 2.6.23.9. Below you find a
patch that fixes that.
Signed-off-by: Florian Zumbiehl <florz@florz.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index e835da8..060bba4 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1637,8 +1637,15 @@
mutex_lock(&u->readlock);
skb = skb_recv_datagram(sk, flags, noblock, &err);
- if (!skb)
+ if (!skb) {
+ unix_state_lock(sk);
+ /* Signal EOF on disconnected non-blocking SEQPACKET socket. */
+ if (sk->sk_type == SOCK_SEQPACKET && err == -EAGAIN &&
+ (sk->sk_shutdown & RCV_SHUTDOWN))
+ err = 0;
+ unix_state_unlock(sk);
goto out_unlock;
+ }
wake_up_interruptible_sync(&u->peer_wait);
