sockatmark(3)
NAME
sockatmark - determine whether socket is at out-of-band mark
SYNOPSIS
#include <sys/socket.h> int sockatmark(int sockfd); Feature Test Macro Requirements for glibc (see feature_test_macros(7)): sockatmark(): _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600
DESCRIPTION
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-ofband mark.
RETURN VALUE
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 is set to indicate the error.
ERRORS
EBADF sockfd is not a valid file descriptor.
- EINVAL sockfd is not a file descriptor to which sockatmark() can be
- applied.
VERSIONS
sockatmark() was added to glibc in version 2.2.4.
CONFORMING TO
POSIX.1-2001.
NOTES
If sockatmark() returns 1, then the out-of-band data can be read using
the MSG_OOB flag of recv(2).
Out-of-band data is only supported 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
Prior to glibc 2.4, sockatmark() did not work.
EXAMPLE
- 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) <= 0);
if (s == -1)perror("read");if (s <= 0)break;}if (atmark == 1) {if (recv(sockfd, &oobdata, 1, MSG_OOB) == -1) {perror("recv");
...}}
SEE ALSO
fcntl(2), recv(2), send(2), tcp(7)
COLOPHON
- This page is part of release 3.25 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.