Since Linux 3.4 there appeared an ability to specify the offset in bytes from which the data will be MSG_PEEK-ed. Describe this socket option in the socket(7) page, where all the other socket options are described. Signed-off-by: Pavel Emelyanov <xemul@xxxxxxxxxxxxx> --- diff --git a/man7/socket.7 b/man7/socket.7 index 2f915da..6177ab1 100644 --- a/man7/socket.7 +++ b/man7/socket.7 @@ -618,6 +618,33 @@ for details on control messages. Gets the socket type as an integer (e.g., .BR SOCK_STREAM ). This socket option is read-only. +.TP +.BR SO_PEEK_OFF " (since Linux 3.4)" +This option controls the behavior of +.BR recv(2) +system call when used with +.BR MSG_PEEK +flag. + +When this value is negative (kernel sets -1 to all new sockets by default) +the behavior of the +.BR recv(2) +is not affected at all. +When it's set to zero or positive value, peeking the data would occur from +the respective position in bytes. At the same time this offset will be +incremented on the amount of bytes peeked from queue, so that the +subsequent attempt to peek the data would result in next data in queue +(similarly, receiving the data from queue without the +.BR MSG_PEEK +flag will result in respectively decreased offset value). +For datagram sockets, if the offset points to the middle of a packet, +the data returned will be marked with the +.BR MSG_TRUNC +flag. + +Since Linux 3.4 this option is supported for +.BR unix(7) +sockets only. .SS Signals When writing onto a connection-oriented socket that has been shut down (by the local or the remote end) -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
