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.
Stefan
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