* [PATCH] vmsplice: relax alignement requirements for SPLICE_F_GIFT
@ 2012-04-04 9:08 Eric Dumazet
2012-04-20 8:19 ` Jens Axboe
0 siblings, 1 reply; 3+ messages in thread
From: Eric Dumazet @ 2012-04-04 9:08 UTC (permalink / raw)
To: Jens Axboe
Cc: linux-kernel, David Miller, netdev, Tom Herbert, Al Viro,
Hugh Dickins, Changli Gao, Andrew Morton, Miklos Szeredi
It seems there is no fundamental reason to limit vmsplice()
SPLICE_F_GIFT to page aligned chunks.
All helpers are prepared to cope with offsets in page.
This limitation makes vmsplice() API very impractical in the zero-copy
land.
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Tom Herbert <therbert@google.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: David Miller <davem@davemloft.net>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Hugh Dickins <hughd@google.com>
Cc: Changli Gao <xiaosuo@gmail.com>
Cc: Miklos Szeredi <mszeredi@suse.cz>
---
fs/splice.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/fs/splice.c b/fs/splice.c
index 5f883de..5417aa3 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -1385,7 +1385,7 @@ static long do_splice(struct file *in, loff_t __user *off_in,
*/
static int get_iovec_page_array(const struct iovec __user *iov,
unsigned int nr_vecs, struct page **pages,
- struct partial_page *partial, int aligned,
+ struct partial_page *partial, bool aligned,
unsigned int pipe_buffers)
{
int buffers = 0, error = 0;
@@ -1623,7 +1623,7 @@ static long vmsplice_to_pipe(struct file *file, const struct iovec __user *iov,
return -ENOMEM;
spd.nr_pages = get_iovec_page_array(iov, nr_segs, spd.pages,
- spd.partial, flags & SPLICE_F_GIFT,
+ spd.partial, false,
pipe->buffers);
if (spd.nr_pages <= 0)
ret = spd.nr_pages;
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] vmsplice: relax alignement requirements for SPLICE_F_GIFT
2012-04-04 9:08 [PATCH] vmsplice: relax alignement requirements for SPLICE_F_GIFT Eric Dumazet
@ 2012-04-20 8:19 ` Jens Axboe
2012-04-20 8:35 ` Eric Dumazet
0 siblings, 1 reply; 3+ messages in thread
From: Jens Axboe @ 2012-04-20 8:19 UTC (permalink / raw)
To: Eric Dumazet
Cc: linux-kernel, David Miller, netdev, Tom Herbert, Al Viro,
Hugh Dickins, Changli Gao, Andrew Morton, Miklos Szeredi
On Wed, Apr 04 2012, Eric Dumazet wrote:
> It seems there is no fundamental reason to limit vmsplice()
> SPLICE_F_GIFT to page aligned chunks.
>
> All helpers are prepared to cope with offsets in page.
>
> This limitation makes vmsplice() API very impractical in the zero-copy
> land.
Sorry for the slow reply on this one. It's been a long time since I
wrote that code... If I recall correctly, the reason it currently
requires alignment, is that a gifted page is no longer yours, by
definition. So the alignment check was to ensure that we gift full
pages. But if the caller screws that up, I guess it's the callers
problem and it's a shame to limit the API in this way.
I will apply it for 3.5.
--
Jens Axboe
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] vmsplice: relax alignement requirements for SPLICE_F_GIFT
2012-04-20 8:19 ` Jens Axboe
@ 2012-04-20 8:35 ` Eric Dumazet
0 siblings, 0 replies; 3+ messages in thread
From: Eric Dumazet @ 2012-04-20 8:35 UTC (permalink / raw)
To: Jens Axboe
Cc: linux-kernel, David Miller, netdev, Tom Herbert, Al Viro,
Hugh Dickins, Changli Gao, Andrew Morton, Miklos Szeredi
On Fri, 2012-04-20 at 10:19 +0200, Jens Axboe wrote:
> On Wed, Apr 04 2012, Eric Dumazet wrote:
> > It seems there is no fundamental reason to limit vmsplice()
> > SPLICE_F_GIFT to page aligned chunks.
> >
> > All helpers are prepared to cope with offsets in page.
> >
> > This limitation makes vmsplice() API very impractical in the zero-copy
> > land.
>
> Sorry for the slow reply on this one. It's been a long time since I
> wrote that code... If I recall correctly, the reason it currently
> requires alignment, is that a gifted page is no longer yours, by
> definition. So the alignment check was to ensure that we gift full
> pages. But if the caller screws that up, I guess it's the callers
> problem and it's a shame to limit the API in this way.
>
> I will apply it for 3.5.
>
Thanks Jens
^ permalink raw reply [flat|nested] 3+ messages in thread
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2012-04-04 9:08 [PATCH] vmsplice: relax alignement requirements for SPLICE_F_GIFT Eric Dumazet
2012-04-20 8:19 ` Jens Axboe
2012-04-20 8:35 ` Eric Dumazet
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