vfs_fileid: add "fstype/mntdir deny/allow list" option
When using the fsname or fsid algorithm a stat() and statfs() call is
required for all mounted file systems to generate the file_id. If e.g.
an NFS file system is unresponsive such a call might block and the smbd
process will become unresponsive. Add "fileid:fstype deny",
"fileid:fstype allow", "fileid:mntdir deny", and "fileid:mntdir allow"
options to ignore potentially unresponsive file systems.
See also https://lists.samba.org/archive/samba-technical/2016-January/111553.html
for a discussion about why this is useful.
Signed-off-by: Ralph Wuerthner <ralph.wuerthner@de.ibm.com>
Reviewed-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>