Messages in this thread |  | | | Date | Wed, 23 Sep 2009 08:01:27 +0200 | | From | Xavier Roche <> | | Subject | Inter-process send()/recv() using zero-copy ? |
Hi folks,
I was wondering if there was a way to have zero-copy send()/recv(), when the socket is connected to the local machine (to another process on the same machine, for example) ?
Such feature would be only feasible with page-aligned blocks, from an a mmap'ed block to another one, I guess.
Typical case:
Process #1 (uid A) buff = mmap(0, size, ..) /* anonymous or not */ ... send(s, buff, size, 0) munmap(buff, size) Process #2 (uid B) buff = mmap(0, size, .. | MAP_ANONYMOUS, ..) recv(s, buff, size, 0) In an ideal fantasy world, the first process would use send() to transmit the complete page-aligned memory block to the other side, and the second process would use recv() to get the memory block on a similar anonymously mmap'ed block, and the only operation the kernel would do would be to share the memory block between the two processes with copy-on-write.
On the real world, the same operation requires a first read of the whole memory block (possibly partially on disk) and a complete write (possibly partially on disk, too) with two copies of the same memory region at the end.
Two solutions can be used to emulate such feature:
1. use a temporary mmap'ed file - but requires a temporary file - permissions for the file ? (not necessarily from the same UID) - special case for local network block transmissions vs. machine-to-machine
2. use shared memory explicitely - handling of permissions ? (ditto) - special case for local network block transmissions vs. machine-to-machine
splice() and friends do not appear to give any help for this case, and I was wondering if there was a chance to do that ?
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