sockatmark(3) - Linux manual page (original) (raw)
sockatmark(3) Library Functions Manual sockatmark(3)
NAME top
sockatmark - determine whether socket is at out-of-band markLIBRARY top
Standard C library (_libc_, _-lc_)SYNOPSIS top
**#include <sys/socket.h>**
**int sockatmark(int** _sockfd_**);**Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
**sockatmark**():
_POSIX_C_SOURCE >= 200112LDESCRIPTION top
**sockatmark**() returns a value indicating whether or not the socket
referred to by the file descriptor _sockfd_ is at the out-of-band
mark. If the socket is at the mark, then 1 is returned; if the
socket is not at the mark, 0 is returned. This function does not
remove the out-of-band mark.RETURN VALUE top
A successful call to **sockatmark**() returns 1 if the socket is at
the out-of-band mark, or 0 if it is not. On error, -1 is returned
and _[errno](../man3/errno.3.html)_ is set to indicate the error.ERRORS top
**EBADF** _sockfd_ is not a valid file descriptor.
**EINVAL** _sockfd_ is not a file descriptor to which **sockatmark**() can
be applied.ATTRIBUTES top
For an explanation of the terms used in this section, see
[attributes(7)](../man7/attributes.7.html).
┌──────────────────────────────────────┬───────────────┬─────────┐
│ **Interface** │ **Attribute** │ **Value** │
├──────────────────────────────────────┼───────────────┼─────────┤
│ **sockatmark**() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘STANDARDS top
POSIX.1-2008.HISTORY top
glibc 2.2.4. POSIX.1-2001.NOTES top
If **sockatmark**() returns 1, then the out-of-band data can be read
using the **MSG_OOB** flag of [recv(2)](../man2/recv.2.html).
Out-of-band data is supported only on some stream socket
protocols.
**sockatmark**() can safely be called from a handler for the **SIGURG**
signal.
**sockatmark**() is implemented using the **SIOCATMARK ioctl**(2)
operation.BUGS top
Prior to glibc 2.4, **sockatmark**() did not work.EXAMPLES top
The following code can be used after receipt of a **SIGURG** signal to
read (and discard) all data up to the mark, and then read the byte
of data at the mark:
char buf[BUF_LEN];
char oobdata;
int atmark, s;
for (;;) {
atmark = sockatmark(sockfd);
if (atmark == -1) {
perror("sockatmark");
break;
}
if (atmark)
break;
s = read(sockfd, buf, BUF_LEN);
if (s == -1)
perror("read");
if (s <= 0)
break;
}
if (atmark == 1) {
if (recv(sockfd, &oobdata, 1, MSG_OOB) == -1) {
perror("recv");
...
}
}SEE ALSO top
[fcntl(2)](../man2/fcntl.2.html), [recv(2)](../man2/recv.2.html), [send(2)](../man2/send.2.html), [tcp(7)](../man7/tcp.7.html)COLOPHON top
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man-pages@man7.orgLinux man-pages 6.10 2024-07-23 sockatmark(3)
Pages that refer to this page:recv(2), signal-safety(7)