linux-kernel - Re: [PATCH 4/4] virtiofs: Support blocking posix locks (fcntl(F

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Date:   Fri, 22 Nov 2019 08:00:42 -0500
From:   Vivek Goyal <vgoyal@...hat.com>
To:     Stefan Hajnoczi <stefanha@...hat.com>
Cc:     virtio-fs@...hat.com, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, dgilbert@...hat.com,
        miklos@...redi.hu
Subject: Re: [PATCH 4/4] virtiofs: Support blocking posix locks
 (fcntl(F_SETLKW))

On Thu, Nov 21, 2019 at 05:00:20PM +0000, Stefan Hajnoczi wrote:

[..]
> > +static int virtio_fs_handle_notify(struct virtio_fs *vfs,
> > +				   struct virtio_fs_notify *notify)
> > +{
> > +	int ret = 0;
> > +	struct fuse_out_header *oh = &notify->out_hdr;
> > +	struct fuse_notify_lock_out *lo;
> > +
> > +	/*
> > +	 * For notifications, oh.unique is 0 and oh->error contains code
> > +	 * for which notification as arrived.
> > +	 */
> > +	switch(oh->error) {
> > +	case FUSE_NOTIFY_LOCK:
> > +		lo = (struct fuse_notify_lock_out *) &notify->outarg;
> > +		notify_complete_waiting_req(vfs, lo);
> > +		break;
> > +	default:
> > +		printk("virtio-fs: Unexpected notification %d\n", oh->error);
> > +	}
> > +	return ret;
> > +}
> 
> Is this specific to virtio or can be it handled in common code?

This is not specific to virtio_fs. In principle, regular fuse daemon could
implement something similar. Though they might not have to because client
can just block without introducing deadlock possibilities.

Anyway, I will look into moving this code into fuse common.

[..]
> > diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
> > index 373cada89815..45f0c4efec8e 100644
> > --- a/include/uapi/linux/fuse.h
> > +++ b/include/uapi/linux/fuse.h
> > @@ -481,6 +481,7 @@ enum fuse_notify_code {
> >  	FUSE_NOTIFY_STORE = 4,
> >  	FUSE_NOTIFY_RETRIEVE = 5,
> >  	FUSE_NOTIFY_DELETE = 6,
> > +	FUSE_NOTIFY_LOCK = 7,
> >  	FUSE_NOTIFY_CODE_MAX,
> >  };
> >  
> > @@ -868,6 +869,12 @@ struct fuse_notify_retrieve_in {
> >  	uint64_t	dummy4;
> >  };
> >  
> > +struct fuse_notify_lock_out {
> > +	uint64_t	id;
> 
> Please call this field "unique" or "lock_unique" so it's clear this
> identifier is the fuse_header_in->unique value of the lock request.

Ok, will do.

Vivek