sockatmark (3) - Linux Man Pages
sockatmark: determine whether socket is at out-of-band mark
sockatmark - determine whether socket is at out-of-band mark
int sockatmark(int sockfd);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
DESCRIPTIONsockatmark() 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 VALUEA 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.
- sockfd is not a valid file descriptor.
- sockfd is not a file descriptor to which sockatmark() can be applied.
VERSIONSsockatmark() was added to glibc in version 2.2.4.
ATTRIBUTESFor an explanation of the terms used in this section, see attributes(7).
CONFORMING TOPOSIX.1-2001, POSIX.1-2008.
NOTESIf 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 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.
BUGSPrior to glibc 2.4, sockatmark() did not work.
EXAMPLEThe 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:
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