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fdpassing-keith-packard
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Merge 2df5f47d3d into 9c79e2b92f

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Nicholas Rishel 2020-06-16 16:23:23 -07:00 committed by GitHub
parent 9c79e2b92f 2df5f47d3d
commit 7e9f8b876e
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3 changed files with 30 additions and 15 deletions
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4
README.md
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@ -303,7 +303,7 @@ Can a file descriptor be passed without sending any data?
And the answer is clearly "no" -- the file descriptor is not passed And the answer is clearly "no" -- the file descriptor is not passed
when no data are included in the write. when no data are included in the write.
(update, 2019-5-8 from Yicholas Rishel) (update, 2019-5-8 from Nicholas Rishel)
This is true for SOCK_STREAM sockets, but for SOCK_SEQPACKET sockets, This is true for SOCK_STREAM sockets, but for SOCK_SEQPACKET sockets,
you *can* do zero-length writes and pass an fd. you *can* do zero-length writes and pass an fd.
@ -316,7 +316,7 @@ you *can* do zero-length writes and pass an fd.
2. failing to accept an fd in the receiver results in the fd being 2. failing to accept an fd in the receiver results in the fd being
closed by the kernel. closed by the kernel.
3. a file descriptor must be accompanied by some data. 3. a file descriptor must be accompanied by some data if sent via stream.
## Make X pass file descriptors ## Make X pass file descriptors

8
fdpass.c
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@ -37,10 +37,15 @@ sock_fd_read(int sock, void *buf, ssize_t bufsize, int *fd, int *nfdp)
int nfd_passed, nfd; int nfd_passed, nfd;
int i; int i;
int *fd_passed; int *fd_passed;
int type;
int length;
iov.iov_base = buf; iov.iov_base = buf;
iov.iov_len = bufsize; iov.iov_len = bufsize;
length = sizeof( int );
getsockopt (sock, SOL_SOCKET, SO_TYPE, &type, &length);
msg.msg_name = NULL; msg.msg_name = NULL;
msg.msg_namelen = 0; msg.msg_namelen = 0;
msg.msg_iov = &iov; msg.msg_iov = &iov;
@ -52,7 +57,7 @@ sock_fd_read(int sock, void *buf, ssize_t bufsize, int *fd, int *nfdp)
perror ("recvmsg"); perror ("recvmsg");
exit(1); exit(1);
} }
if (size > 0 && pass.cmsghdr.cmsg_len > sizeof (struct cmsghdr)) { if ((size > 0 || type == SOCK_SEQPACKET) && pass.cmsghdr.cmsg_len > sizeof (struct cmsghdr)) {
if ((msg.msg_flags & MSG_TRUNC) || if ((msg.msg_flags & MSG_TRUNC) ||
(msg.msg_flags & MSG_CTRUNC)) { (msg.msg_flags & MSG_CTRUNC)) {
fprintf (stderr, "control message truncated"); fprintf (stderr, "control message truncated");
@ -68,7 +73,6 @@ sock_fd_read(int sock, void *buf, ssize_t bufsize, int *fd, int *nfdp)
pass.cmsghdr.cmsg_type); pass.cmsghdr.cmsg_type);
exit(1); exit(1);
} }
nfd_passed = (pass.cmsghdr.cmsg_len - sizeof (struct cmsghdr)) / sizeof (int); nfd_passed = (pass.cmsghdr.cmsg_len - sizeof (struct cmsghdr)) / sizeof (int);
fd_passed = (int *) CMSG_DATA(&pass.cmsghdr); fd_passed = (int *) CMSG_DATA(&pass.cmsghdr);

33
zerowrite.c
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@ -25,17 +25,28 @@ child(int sock)
ssize_t size; ssize_t size;
sleep(1); sleep(1);
for (;;) { size = sock_fd_read(sock, buf, sizeof(buf), NULL, NULL);
nfd = 1; if (size <= 0) {
size = sock_fd_read(sock, buf, sizeof(buf), &fd, &nfd); printf ("<=0");
if (size <= 0) return;
break;
printf ("read %d nfd %d\n", size, nfd);
if (nfd == 1) {
write(fd, "hello, world\n", 13);
close(fd);
}
} }
printf ("read %d\n", size);
nfd = 1;
size = sock_fd_read(sock, buf, sizeof(buf), &fd, &nfd);
printf ("read %d nfd %d\n", size, nfd);
if (nfd == 1) {
write(fd, "hello, world\n", 13);
close(fd);
}
size = sock_fd_read(sock, buf, sizeof(buf), NULL, NULL);
if (size <= 0) {
printf ("<=0");
return;
}
printf ("read %d\n", size);
} }
void void
@ -60,7 +71,7 @@ main(int argc, char **argv)
int sv[2]; int sv[2];
int pid; int pid;
if (socketpair(AF_LOCAL, SOCK_STREAM, 0, sv) < 0) { if (socketpair(AF_LOCAL, SOCK_SEQPACKET, 0, sv) < 0) {
perror("socketpair"); perror("socketpair");
exit(1); exit(1);
} }