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 <[EMAIL PROTECTED]>
> > > > >
> > > > > 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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