diff options
| author | Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com> | 2017-07-19 22:47:14 -0400 |
|---|---|---|
| committer | Michael Kerrisk <mtk.manpages@gmail.com> | 2017-08-16 02:29:29 +0200 |
| commit | cf699fb57e4c480f736a752b50d1e9fd40d809ef (patch) | |
| tree | 17482908069f9df407a80802796ad49956128ece /man3/cmsg.3 | |
| parent | d8026103cbe52ac8104a49ced041520c2bd42f27 (diff) | |
| download | man-pages-cf699fb57e4c480f736a752b50d1e9fd40d809ef.tar.gz | |
cmsg.3: Add a scatter/gather buffer to sample code
Add a simple scatter/gather buffer to the cmsg sample code.
It appears that the scatter/gather buffer is required even though
it may not be used. In my testing (on Fedora 24
4.8.7-200.fc24.x86_64 as well as a 4.11 based kernel) return value
of sendmsg() was the number of bytes in the scatter/gather buffer
(1 with the patch below).
Without the iovec buffer, sendmsg() returns 0 which means no bytes
were transferred and the corresponding recvmsg() blocks
indefinitely.
Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Diffstat (limited to 'man3/cmsg.3')
| -rw-r--r-- | man3/cmsg.3 | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/man3/cmsg.3 b/man3/cmsg.3 index a537a0c69b..060b96fd8c 100644 --- a/man3/cmsg.3 +++ b/man3/cmsg.3 @@ -200,12 +200,19 @@ struct msghdr msg = { 0 }; struct cmsghdr *cmsg; int myfds[NUM_FD]; /* Contains the file descriptors to pass */ int *fdptr; +char iobuf[1]; +struct iovec io = { + .iov_base = iobuf, + .iov_len = sizeof(iobuf) +}; union { /* Ancillary data buffer, wrapped in a union in order to ensure it is suitably aligned */ char buf[CMSG_SPACE(sizeof(myfds))]; struct cmsghdr align; } u; +msg.msg_iov = &io; +msg.msg_iovlen = 1; msg.msg_control = u.buf; msg.msg_controllen = sizeof(u.buf); cmsg = CMSG_FIRSTHDR(&msg); |