From: Stefan Hajnoczi <stefanha@redhat.com>
To: "misono.tomohiro@fujitsu.com" <misono.tomohiro@fujitsu.com>
Cc: "virtio-fs@redhat.com" <virtio-fs@redhat.com>,
'Miklos Szeredi' <mszeredi@redhat.com>,
"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>
Subject: Re: [Virtio-fs] [PATCH 0/2] virtiofsd: Two fix for xattr operation
Date: Fri, 25 Oct 2019 14:54:16 +0200 [thread overview]
Message-ID: <20191025125416.GE13314@stefanha-x1.localdomain> (raw)
In-Reply-To: <OSBPR01MB3783A810FEC4C2F3AE7248BAE56B0@OSBPR01MB3783.jpnprd01.prod.outlook.com>
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On Wed, Oct 23, 2019 at 11:42:50AM +0000, misono.tomohiro@fujitsu.com wrote:
> > -----Original Message-----
> > From: Stefan Hajnoczi [mailto:stefanha@redhat.com]
> > Sent: Monday, October 21, 2019 6:41 PM
> > To: Misono, Tomohiro/味曽野 智礼 <misono.tomohiro@fujitsu.com>
> > Cc: 'Miklos Szeredi' <mszeredi@redhat.com>; virtio-fs@redhat.com; qemu-devel@nongnu.org
> > Subject: Re: [Virtio-fs] [PATCH 0/2] virtiofsd: Two fix for xattr operation
> >
> > On Fri, Oct 18, 2019 at 08:51:20AM +0000, misono.tomohiro@fujitsu.com wrote:
> > > > Doing unshare(CLONE_FS) after thread startup seems safe, though must
> > > > be careful to change the working directory to the root of the mount
> > > > *before* starting any threads.
> > >
> > > I think working directry is changed in setup_sandbox() -> setup_mount_namespace() -> setup_pivot_root().
> > > So, can we just add unshare(CLONE_FS) in fv_queue_worker()?
> >
> > fv_queue_worker() is the thread pool worker function that is called for each request. Calling unshare(CLONE_FS) for each request
> > is not necessary and will reduce performance.
> >
> > A thread-local variable can be used to avoid repeated calls to
> > unshare(CLONE_FS) from the same worker thread:
> >
> > static __thread bool clone_fs_called;
> >
> > static void fv_queue_worker(gpointer data, gpointer user_data)
> > {
> > ...
> > if (!clone_fs_called) {
> > int ret;
> >
> > ret = unshare(CLONE_FS);
> > assert(ret == 0); /* errors not expected according to man page */
> >
> > clone_fs_called = true;
> > }
> >
> > Another issue is the seccomp policy. Since worker threads are spawned at runtime it is necessary to add the unshare(2) syscall
> > to the seccomp whitelist in contrib/virtiofsd/seccomp.c.
> >
>
> Thanks for suggesting.
>
> I tried above code with fchdir() + ...xattr() + fchdir() in lo_...xattr
> and it solves all the problem about xattr I see.
>
> However, it seems the fix causes some performance issue in stress test
> as ACL check issues getxattr() and a lot of fchdir() happens. So, I may
> try to combine the old method for regular file and this method for special
> files.
Sounds good.
Stefan
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next prev parent reply other threads:[~2019-10-25 12:56 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-16 10:37 [PATCH 0/2] virtiofsd: Two fix for xattr operation Misono Tomohiro
2019-10-16 10:37 ` [PATCH 1/2] virtiofsd: Avoid process hang when doing xattr operation to FIFO Misono Tomohiro
2019-10-16 10:37 ` [PATCH 2/2] virtiofsd: Allow setxattr operation to directry Misono Tomohiro
2019-10-17 10:05 ` [Virtio-fs] [PATCH 0/2] virtiofsd: Two fix for xattr operation Stefan Hajnoczi
2019-10-17 11:23 ` Miklos Szeredi
2019-10-17 13:01 ` Miklos Szeredi
2019-10-17 15:25 ` Vivek Goyal
2019-10-17 15:45 ` Miklos Szeredi
2019-10-17 16:09 ` Stefan Hajnoczi
2019-10-17 16:48 ` Miklos Szeredi
2019-10-18 7:16 ` Miklos Szeredi
2019-10-18 8:51 ` misono.tomohiro
2019-10-21 9:40 ` Stefan Hajnoczi
2019-10-23 11:42 ` misono.tomohiro
2019-10-25 12:54 ` Stefan Hajnoczi [this message]
2019-10-18 10:09 ` Stefan Hajnoczi
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