Messages in this thread | | | Date | Thu, 5 Nov 2009 17:25:54 +0100 | From | Max Kellermann <> | Subject | Re: [PATCH] pipe: don't block after data has been written |
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On 2009/11/05 17:20, Américo Wang <xiyou.wangcong@gmail.com> wrote: > On Thu, Nov 05, 2009 at 04:31:47PM +0100, Max Kellermann wrote: > >According to the select() / poll() documentation, a write operation on > >a file descriptor which is "ready for writing" must not block. Linux > >violates this rule: if you pass a very large buffer to write(), the > >system call will not return until everything is written, or an error > >occurs. > > > >This patch adds a simple check: if at least one byte has already been > >written, break from the loop, instead of calling pipe_wait(). > > Do you have any working test-case for this?
Eric Dumazet posted a program earlier today (in response to my pipe/splice patch):
http://lkml.org/lkml/2009/11/5/144
With this patch applied, it runs correctly (without it, the write() blocks until the consumer has read everything):
poll([{fd=4, events=POLLOUT}], 1, -1) = 1 ([{fd=4, revents=POLLOUT}]) [...] write(4, "\0\0\0\0"..., 1000000) = 65536 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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