[PATCH] fs/splice: ignore flag SPLICE_F_GIFT in syscall vmsplice

[PATCH] fs/splice: ignore flag SPLICE_F_GIFT in syscall vmsplice

[Konstantin Khlebnikov]

Generic support of flag SPLICE_F_MOVE in syscall splice was removed in
kernel 2.6.21 commit 485ddb4b9741 ("1/2 splice: dont steal").
Infrastructure stay intact and this feature may came back.
At least driver or filesystem could provide own implementation.

But stealing mapped pages from userspace never worked and is very
unlikely that will ever make sense due to unmapping overhead.
Also lru handling is broken if gifted anon page spliced into file.

Let's seal entry point for marking page as a gift in vmsplice.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Link: https://lore.kernel.org/lkml/CAHk-=wgPQutQ8d8kUCvAFi+hfNWgaNLiZPkbg-GXY2DCtD-Z5Q@mail.gmail.com/
---
 fs/splice.c |    3 ---
 1 file changed, 3 deletions(-)

diff --git a/fs/splice.c b/fs/splice.c
index 98412721f056..71dbdd78bfd1 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -1288,9 +1288,6 @@ static long vmsplice_to_pipe(struct file *file, struct iov_iter *iter,
 	long ret = 0;
 	unsigned buf_flag = 0;
 
-	if (flags & SPLICE_F_GIFT)
-		buf_flag = PIPE_BUF_FLAG_GIFT;
-
 	pipe = get_pipe_info(file);
 	if (!pipe)
 		return -EBADF;

Re: [PATCH] fs/splice: ignore flag SPLICE_F_GIFT in syscall vmsplice

[Christoph Hellwig]

On Sun, Nov 10, 2019 at 01:01:23PM +0300, Konstantin Khlebnikov wrote:
> Generic support of flag SPLICE_F_MOVE in syscall splice was removed in
> kernel 2.6.21 commit 485ddb4b9741 ("1/2 splice: dont steal").
> Infrastructure stay intact and this feature may came back.
> At least driver or filesystem could provide own implementation.
> 
> But stealing mapped pages from userspace never worked and is very
> unlikely that will ever make sense due to unmapping overhead.
> Also lru handling is broken if gifted anon page spliced into file.
> 
> Let's seal entry point for marking page as a gift in vmsplice.

Please kill off PIPE_BUF_FLAG_GIFT entirely, there is no need to keep
dead code around.  Anyone who cares enough can resurrect it from git
history.