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splice: fix misuse of SPLICE_F_NONBLOCK 

SPLICE_F_NONBLOCK is clearly documented to only affect blocking on the
pipe.  In __generic_file_splice_read(), however, it causes an EAGAIN
if the page is currently being read.

This makes it impossible to write an application that only wants
failure if the pipe is full.  For example if the same process is
handling both ends of a pipe and isn't otherwise able to determine
whether a splice to the pipe will fill it or not.

We could make the read non-blocking on O_NONBLOCK or some other splice
flag, but for now this is the simplest fix.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
CC: stable@kernel.org
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
This commit is contained in:
Miklos Szeredi 2010-08-03 12:48:50 +02:00 committed by Jens Axboe
parent 7901d14144
commit 6965031d33
1 changed files with 1 additions and 11 deletions
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12
fs/splice.c
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@ -399,17 +399,7 @@ __generic_file_splice_read(struct file *in, loff_t *ppos,
* If the page isn't uptodate, we may need to start io on it
*/
if (!PageUptodate(page)) {
/*
* If in nonblock mode then dont block on waiting
* for an in-flight io page
*/
if (flags & SPLICE_F_NONBLOCK) {
if (!trylock_page(page)) {
error = -EAGAIN;
break;
}
} else
lock_page(page);
lock_page(page);
/*
* Page was truncated, or invalidated by the