Messages in this thread | | | From | "Manfred Spraul" <> | Subject | Re: Feedback for fastselect and one-copy-pipe | Date | Mon, 12 Mar 2001 19:42:18 +0100 |
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From: <kuznet@ms2.inr.ac.ru> > Hello! > > > * davem's patch breaks apps that assume that write(,PIPE_BUF) after > > poll(POLLOUT) never blocks, even for blocking pipes. > > Pardon, but PIPE_BUF <= PAGE_SIZE yet, so that fears have no reasons. >
The difference is the =
> <<<<< davem's patch > + if (count >= PAGE_SIZE && > ^^ > + !(filp->f_flags & O_NONBLOCK)) { > <<<<<<< my patch > + if (count > PIPE_BUF && chars == PIPE_SIZE && ^ > + (!(filp->f_flags & O_NONBLOCK))) { > <<<<<<<
davem used >=, I used >. All other differences between our patches are code cleanups.
Just try this on i386: (PIPE_BUF is defined to 4096 on i386 - I really don't understand why, but now it's too late to reverse it back to 512)
<<<< char buf[PIPE_BUF]; void main() { int pipes[2]; pipe(pipes); write(pipes[1],buf,sizeof(buf)); } <<<<<<<
It returns immediately on all unix platforms I tested, including all linux versions, except with davem's patch. It's not guaranteed in sus or posix, but I'm reluctant to change it.
-- Manfred
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