Messages in this thread | | | Date | Thu, 15 Jan 2009 12:47:22 +0100 | From | Eric Dumazet <> | Subject | Re: maximum buffer size for splice(2) tcp->pipe? |
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David Miller a écrit : > From: Eric Dumazet <dada1@cosmosbay.com> > Date: Wed, 14 Jan 2009 00:38:32 +0100 > >> [PATCH] net: splice() from tcp to socket should take into account O_NONBLOCK >> >> Instead of using SPLICE_F_NONBLOCK to select a non blocking mode both on >> source tcp socket and pipe destination, we use the underlying file flag (O_NONBLOCK) >> for selecting a non blocking socket. >> >> Signed-off-by: Eric Dumazet <dada1@cosmosbay.com> > > This needs at least some more thought. > > It seems, for one thing, that this change will interfere with the > intentions of the code in splice_dirt_to_actor which goes: > > /* > * Don't block on output, we have to drain the direct pipe. > */ > sd->flags &= ~SPLICE_F_NONBLOCK;
Reading splice_direct_to_actor() I see nothing wrong with the patch
(Patch is about splice from socket to pipe, while the sd->flags you mention in splice_direct_to_actor() only applies to the splice from internal pipe to something else, as splice_direct_to_actor() allocates an internal pipe to perform its work.
Also, the meaning of SPLICE_F_NONBLOCK, as explained in include/linux/splice.h is :
#define SPLICE_F_NONBLOCK (0x02) /* don't block on the pipe splicing (but */ /* we may still block on the fd we splice */ /* from/to, of course */
If the comment is still correct, SPLICE_F_NONBLOCK only applies to the pipe implied in splice() syscall.
For the other file, either its : - A regular file : nonblocking mode is not available, like a normal read()/write() syscall
- A socket : We should be able to specify if its blocking or not, independantly from the SPLICE_F_NONBLOCK flag that only applies to the pipe. Normal way is using ioctl(FIONBIO) or other fcntl() call to change file->f_flags O_NONBLOCK
In order to be able to efficiently use splice() from a socket to a file, we need to do a loop of :
{ splice(from blocking tcp socket to non blocking pipe, SPLICE_F_NONBLOCK); /* nonblocking pipe or risk deadlock */ splice(from pipe to file) }
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