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

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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@xxxxxxxxxxxxxx <mailto:reddyn@xxxxxxxxxxxxxx>> 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.

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