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__SKB_TRY_RECV_DATAG(9) Linux Networking __SKB_TRY_RECV_DATAG(9)


__skb_try_recv_datagram - Receive a datagram skbuff


struct sk_buff * __skb_try_recv_datagram(struct sock * sk, unsigned int flags, int * peeked, int * off, int * err, struct sk_buff ** last);





MSG_ flags


returns non-zero if this packet has been seen before


an offset in bytes to peek skb from. Returns an offset within an skb where data actually starts


error code returned


set to last peeked message to inform the wait function what to look for when peeking


Get a datagram skbuff, understands the peeking, nonblocking wakeups and possible races. This replaces identical code in packet, raw and udp, as well as the IPX AX.25 and Appletalk. It also finally fixes the long standing peek and read race for datagram sockets. If you alter this routine remember it must be re-entrant.

This function will lock the socket if a skb is returned, so the caller needs to unlock the socket in that case (usually by calling skb_free_datagram). Returns NULL with *err set to -EAGAIN if no data was available or to some other value if an error was detected.

* It does not lock socket since today. This function is * free of race conditions. This measure should/can improve * significantly datagram socket latencies at high loads, * when data copying to user space takes lots of time. * (BTW I've just killed the last cli in IP/IPv6/core/netlink/packet * 8) Great win.) * --ANK (980729)

The order of the tests when we find no data waiting are specified quite explicitly by POSIX 1003.1g, don't change them without having the standard around please.


January 2017 Kernel Hackers Manual 4.8.