On Wed, Oct 23, 2019 at 11:42:50AM +0000, misono.tomoh...@fujitsu.com wrote: > > -----Original Message----- > > From: Stefan Hajnoczi [mailto:stefa...@redhat.com] > > Sent: Monday, October 21, 2019 6:41 PM > > To: Misono, Tomohiro/味曽野 智礼 <misono.tomoh...@fujitsu.com> > > Cc: 'Miklos Szeredi' <mszer...@redhat.com>; virtio...@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.tomoh...@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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