SOCKATMARK(3) Linux Programmer's Manual SOCKATMARK(3)NAMEsockatmark - determine whether socket is at out-of-band mark
SYNOPSIS
#include <sys/socket.h>
int sockatmark(int fd);
DESCRIPTIONsockatmark() returns a value indicating whether or not the socket
referred to by the file descriptor fd 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
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 fd is not a valid file descriptor.
EINVAL fd is not a file descriptor to which sockatmark() can be
applied.
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() operation.
CONFORMING TO
POSIX.1-2001
VERSIONSsockatmark() was added to glibc in version 2.2.4.
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(fd);
if (atmark == -1) {
perror("sockatmark");
break;
}
if (atmark)
break;
s = read(fd, buf, BUF_LEN) <= 0);
if (s == -1)
perror("read");
if (s <= 0)
break;
}
if (atmark == 1) {
if (recv(fd, &oobdata, 1, MSG_OOB) == -1) {
perror("recv");
...
}
}
SEE ALSOfcntl(2), recv(2), send(2), tcp(7)Linux 2006-04-24 SOCKATMARK(3)
