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From: Vivek Goyal <vgoyal@redhat.com>
To: Miklos Szeredi <mszeredi@redhat.com>
Cc: Greg Kurz <groug@kaod.org>,
	QEMU Developers <qemu-devel@nongnu.org>,
	kvm@vger.kernel.org, "Michael S. Tsirkin" <mst@redhat.com>,
	Cornelia Huck <cohuck@redhat.com>,
	virtio-fs-list <virtio-fs@redhat.com>,
	Miklos Szeredi <miklos@szeredi.hu>,
	Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [Virtio-fs] [for-6.1 v3 3/3] virtiofsd: Add support for FUSE_SYNCFS request
Date: Tue, 11 May 2021 10:49:23 -0400	[thread overview]
Message-ID: <20210511144923.GA238488@horse> (raw)
In-Reply-To: <20210511125409.GA234533@horse>

On Tue, May 11, 2021 at 08:54:09AM -0400, Vivek Goyal wrote:
> On Tue, May 11, 2021 at 02:31:14PM +0200, Miklos Szeredi wrote:
> > On Mon, May 10, 2021 at 5:55 PM Greg Kurz <groug@kaod.org> wrote:
> > >
> > > Honor the expected behavior of syncfs() to synchronously flush all data
> > > and metadata on linux systems. Simply loop on all known submounts and
> > > call syncfs() on them.
> > 
> > Why not pass the submount's root to the server, so it can do just one
> > targeted syncfs?
> > 
> > E.g. somehting like this in fuse_sync_fs():
> > 
> > args.nodeid = get_node_id(sb->s_root->d_inode);
> 
> Hi Miklos,
> 
> I think current proposal was due to lack of full understanding on my part.
> I was assuming we have one super block in client and that's not the case
> looks like. For every submount, we will have another superblock known
> to vfs, IIUC. That means when sync() happens, we will receive ->syncfs()
> for each of those super blocks. And that means file server does not
> have to keep track of submounts explicitly and it will either receive
> a single targeted SYNCFS (for the case of syncfs(fd)) or receive
> multile SYNCFS calls (one for each submount when sync() is called).

Tried sync() with submounts enabled and we are seeing a SYNCFS call
only for top level super block and not for submounts.

Greg noticed that it probably is due to the fact that iterate_super()
skips super blocks which don't have SB_BORN flag set. 

Only vfs_get_tree() seems to set SB_BORN and for our submounts we
are not calling vfs_get_tree(), hence SB_BORN is not set. NFS seems
to call vfs_get_tree() and hence SB_BORN must be set for submounts.

Maybe we need to modify virtio_fs_get_tree() so that it can deal with
mount as well as submounts and then fuse_dentry_automount() should
probably call vfs_get_tree() and that should set SB_BORN and hopefully
sync() will work with it. Greg is planning to give it a try.

Does it sound reasonable.

Thanks
Vivek


  reply	other threads:[~2021-05-11 14:49 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-10 15:55 [for-6.1 v3 0/3] virtiofsd: Add support for FUSE_SYNCFS request Greg Kurz
2021-05-10 15:55 ` [for-6.1 v3 2/3] virtiofsd: Track mounts Greg Kurz
2021-05-10 19:18   ` Vivek Goyal
2021-05-11 10:06     ` Greg Kurz
2021-05-10 15:55 ` [for-6.1 v3 3/3] virtiofsd: Add support for FUSE_SYNCFS request Greg Kurz
2021-05-10 19:15   ` Vivek Goyal
2021-05-11 10:09     ` Greg Kurz
2021-05-11 12:31   ` [Virtio-fs] " Miklos Szeredi
2021-05-11 12:54     ` Vivek Goyal
2021-05-11 14:49       ` Vivek Goyal [this message]
2021-05-11 15:08         ` Miklos Szeredi
2021-05-11 15:16           ` Vivek Goyal
2021-05-11 15:08     ` Greg Kurz
2021-05-10 15:58 ` [for-6.1 v3 0/3] " Greg Kurz
2021-11-10 19:48 ` Vivek Goyal
2021-11-15 14:30   ` Greg Kurz

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