linux-kernel - [PATCH] fs/splice: ignore flag SPLICE_F

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Date:   Sun, 10 Nov 2019 13:01:23 +0300
From:   Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
To:     linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>
Cc:     David Howells <dhowells@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Miklos Szeredi <miklos@...redi.hu>
Subject: [PATCH] fs/splice: ignore flag SPLICE_F_GIFT in syscall vmsplice

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@...dex-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;