Messages in this thread Patch in this message | | | Date | Wed, 20 Feb 2008 10:35:28 +0100 | From | Jens Axboe <> | Subject | Re: [PATCH] splice: fix problem with sys_tee and SPLICE_F_NONBLOCK |
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On Tue, Feb 19 2008, Johann Felix Soden wrote: > > Am Dienstag, den 19.02.2008, 22:25 +0100 schrieb Jens Axboe: > > On Tue, Feb 19 2008, Johann Felix Soden wrote: > > > > On Tue, Feb 19 2008, Johann Felix Soden wrote: > > > > > From: Johann Felix Soden <johfel@users.sourceforge.net> > > > > > > > > > > With SPLICE_F_NONBLOCK sys_tee should return number of duplicated bytes, > > > > > not only -EAGAIN on success. > > > > > > > > ? > > > > > > > > The current behaviour is to return bytes tee'd, or return -EAGAIN for > > > > zero bytes if SPLICE_F_NONBLOCK is set. It doesn't return "-EAGAIN on > > > > success", not sure what you mean there. > > > > > > > Sorry, my patch description was not correct. > > > > > > The new behavior of sys_tee with my patch is: > > > - return -EAGAIN if there are no data in the pipe, but writer > > > connected to the pipe, > > > - return 0 if there are not writers connected > > > - else return number of duplicated byte > > > > > > The old behavior was: return -EAGAIN or the number (>0) of duplicated > > > bytes. > > > > Your patch has an odd way of achieving that goal, modify the real > > location of the assignment instead of overriding something. That has the > > potential to turn into another confusing bug later on, wondering why the > > heck your return value isn't being passed back. > > > > Improvement is welcome though, you can't distuingish -EAGAIN on the > > input side from the output side currently. > > > > I thought again about the problem and my patch: you are right, the patch > is nonsense. I have learnt, that the correctness of a patch is not > guaranteed by the (bad, but anyhow working) solution of the problem the > patch was written for. > Sorry for wasting your time.
Don't worry, it's not a waste of time even though your solution isn't the correct one.
When non-blocking is set, ideally we want to return 0 if there's no hope of anymore data and EAGAIN if trying later may yield some data. So how about this instead?
diff --git a/fs/splice.c b/fs/splice.c index 9b559ee..0670c91 100644 --- a/fs/splice.c +++ b/fs/splice.c @@ -1669,6 +1669,13 @@ static int link_pipe(struct pipe_inode_info *ipipe, i++; } while (len); + /* + * return EAGAIN if we have the potential of some data in the + * future, otherwise just return 0 + */ + if (!ret && ipipe->waiting_writers && (flags & SPLICE_F_NONBLOCK)) + ret = -EAGAIN; + inode_double_unlock(ipipe->inode, opipe->inode); /* @@ -1709,11 +1716,8 @@ static long do_tee(struct file *in, struct file *out, size_t len, ret = link_ipipe_prep(ipipe, flags); if (!ret) { ret = link_opipe_prep(opipe, flags); - if (!ret) { + if (!ret) ret = link_pipe(ipipe, opipe, len, flags); - if (!ret && (flags & SPLICE_F_NONBLOCK)) - ret = -EAGAIN; - } } } -- Jens Axboe
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