linux-kernel - Re: [fuse-devel] [PATCH v4] fuse: Add support for passthrough read/write

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Date:	Mon, 25 Jan 2016 12:49:00 -0800
From:	Nikhilesh Reddy <reddyn@...eaurora.org>
To:	Mike Shal <marfey@...il.com>
CC:	torvalds@...ux-foundation.org, Miklos Szeredi <miklos@...redi.hu>,
	fuse-devel <fuse-devel@...ts.sourceforge.net>,
	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	gregkh@...uxfoundation.org, linux-fsdevel@...r.kernel.org,
	viro@...iv.linux.org.uk,
	Richard Weinberger <richard.weinberger@...il.com>,
	Theodore Ts'o <tytso@....edu>, jack@...e.cz,
	Antonio SJ Musumeci <trapexit@...wn.link>, sven.utcke@....de,
	Nikolaus Rath <nikolaus@...h.org>,
	Jann Horn <jannhorn@...glemail.com>
Subject: Re: [fuse-devel] [PATCH v4] fuse: Add support for passthrough read/write

On Fri 22 Jan 2016 03:04:36 PM PST, Mike Shal wrote:
> On Wed, Jan 20, 2016 at 7:16 PM, Nikhilesh Reddy
> <reddyn@...eaurora.org <mailto:reddyn@...eaurora.org>> wrote:
>
>     diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
>     @@ -569,6 +570,8 @@ ssize_t fuse_simple_request(struct fuse_conn
>     *fc, struct fuse_args *args)
>             if (!ret && args->out.argvar) {
>                     BUG_ON(args->out.numargs != 1);
>                     ret = req->out.args[0].size;
>     +               if (req->passthrough_filp != NULL)
>     +                       args->out.passthrough_filp =
>     req->passthrough_filp;
>             }
>             fuse_put_request(fc, req);
>
>
> Is it correct to only set passthrough_filp when args->out.argvar is
> set here? I tried to test your patch, but I'm still seeing read &
> write requests to my FUSE filesystem after setting the passthrough
> bit. As far as I can tell, args->out.argvar is only set in a few cases
> (like fuse_follow_link()) but not where you're using it in
> fuse_create_open() or fuse_send_open(). I changed the logic to this:
>
> diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
> index 5cc5385..543c250 100644
> --- a/fs/fuse/dev.c
> +++ b/fs/fuse/dev.c
> @@ -567,11 +567,14 @@ ssize_t fuse_simple_request(struct fuse_conn
> *fc, struct fuse_args *args)
>                args->out.numargs * sizeof(struct fuse_arg));
>         fuse_request_send(fc, req);
>         ret = req->out.h.error;
> +       if (!ret) {
> +               if (req->passthrough_filp != NULL) {
> +                       args->out.passthrough_filp =
> req->passthrough_filp;
> +               }
> +       }
>         if (!ret && args->out.argvar) {
>                 BUG_ON(args->out.numargs != 1);
>                 ret = req->out.args[0].size;
> -               if (req->passthrough_filp != NULL)
> -                       args->out.passthrough_filp =
> req->passthrough_filp;
>         }
>         fuse_put_request(fc, req);
>
> And then it worked as expected. The only read() calls I see in my FUSE
> filesystem after this change are from mmaped files, but it sounds like
> you're already working on that. The performance is much improved for
> large reads & writes, so thanks for working on this! I'm excited to
> see it finished.
>
> Note that I had to implement the libfuse side of things myself to test
> this, so it's possible I'm doing something wrong there to trigger this
> behavior. Maybe you could post your libfuse patches somewhere as well?
> Then I can make sure I'm testing the same thing that you are.
>
> Thanks,
> -Mike
>
>

Hi
Thank you so much Mike for testing it out and reporting the results.
I reviewed my code base again and it turns out i have other internal  
patches that allow my code to work.
But you are right i can fix up the code simliar to your suggestion in 
the next patch so it works no matter what.
I will wait one or two more days before sending out a new patch with 
the fix up as suggested. ( credit to you of course ) so that others 
have a chance to give more comments.
I hope you can help test it out then as well.

As for libfuse i currently testing using a proprietary version of a 
daemon that doesnt use libfuse so i dont have have a patch out yet. 
(the legal guys are to blame)
If you you have one ready can you please post it ? ( will save me the 
effort :)  and the bureaucracy i have to go through to post a patch ) 
otherwise will try to get my version out by end of the month


Again thanks for your help and support

--
Thanks
Nikhilesh Reddy

Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora 
Forum,
a Linux Foundation Collaborative Project.