linux-kernel - Re: [fuse-devel] [PATCH] fuse: Fix fuse_get_user

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Date:	Mon, 25 Apr 2016 13:03:57 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	Seth Forshee <seth.forshee@...onical.com>
Cc:	Ashish Samant <ashish.samant@...cle.com>,
	fuse-devel <fuse-devel@...ts.sourceforge.net>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [fuse-devel] [PATCH] fuse: Fix fuse_get_user_pages() return value

On Wed, Apr 20, 2016 at 5:43 PM, Seth Forshee
<seth.forshee@...onical.com> wrote:
> On Tue, Apr 19, 2016 at 03:57:52PM -0700, Ashish Samant wrote:
>> Hi Seth,
>> On 04/19/2016 03:43 PM, Seth Forshee wrote:
>> >fuse_direct_io() expects this to return either 0 or a negative
>> >error code, but on success it may return a positive value.
>> >fuse_direct_io() may return this same value when the subsequent
>> >I/O operation doesn't transfer any data, which means that it will
>> >return a positive value when no bytes were transferred. This is
>> >obviously problematic.
>> >
>> >Fix fuse_get_user_pages() to return 0 on success. This will in
>> >turn make it so that fuse_direct_io() returns 0 if no bytes are
>> >transferred.
>> >
>> >Fixes: 742f992708df ("fuse: return patrial success from fuse_direct_io()")
>> >Signed-off-by: Seth Forshee <seth.forshee@...onical.com>
>> >---
>> >  fs/fuse/file.c | 2 +-
>> >  1 file changed, 1 insertion(+), 1 deletion(-)
>> >
>> >diff --git a/fs/fuse/file.c b/fs/fuse/file.c
>> >index b5c616c5ec98..78af5c0996b8 100644
>> >--- a/fs/fuse/file.c
>> >+++ b/fs/fuse/file.c
>> >@@ -1295,7 +1295,7 @@ static int fuse_get_user_pages(struct fuse_req *req, struct iov_iter *ii,
>> >     *nbytesp = nbytes;
>> >-    return ret;
>> >+    return ret < 0 ? ret : 0;
>> >  }
>> >  static inline int fuse_iter_npages(const struct iov_iter *ii_p)
>>
>>
>> I have already sent a patch to the list that does exactly the same thing :)
>>
>> https://sourceforge.net/p/fuse/mailman/message/34966327/
>
> Oops, should have checked the list first I guess :-)
>
> But that's from several weeks ago, and it's still not applied? This is
> causing big problems for lxcfs on 4.6-rc kernels, so it's definitely a
> regression and needs to get fixed.

Applied, thanks.

Miklos