Way back when I rewrote busybox mount 3 times, and now I'm writing a mount implementation for toybox, and this means I'm going through the list of VFS flags in include/linux/fs.h and trying to figure out what they all _do_. I _think_ there are three flags missing from the list filtered out in fs/namespace.c function do_mount(), specifically: diff --git a/fs/namespace.c b/fs/namespace.c index 1e4a5fe..83c9c49 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -2175,7 +2175,7 @@ long do_mount(char *dev_name, char *dir_name, char *type_page, flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE | MS_BORN | MS_NOATIME | MS_NODIRATIME | MS_RELATIME| MS_KERNMOUNT | - MS_STRICTATIME); + MS_STRICTATIME | MS_NOSEC | MS_NOUSER | MS_POSIXACL); if (flags & MS_REMOUNT) retval = do_remount(&path, flags & ~MS_REMOUNT, mnt_flags, "MS_NOUSER" tells attempts to mount this filesystem to fail (for pipefs and such) and you can set it yourself, meaning the attempt to mount will always fail. Not a big problem but: dude? (This is not the same thing as user/nouser in fstab, that's internal to the userspace mount command.) MS_POSIXACL tells the VFS layer the filesystem wants it to track extended attributes. The flag is set by each filesystem as appropriate, and most of them clear it first but SOME DON'T. (What happens if you pass MS_POSIXACL to mount when mounting jffs2 with access control list support disabled in the filesystem but enabled in the VFS? Beats me.) MS_NOSEC is... weird. It's unconditionally set in fs/super.c function mount_bdev() on first mount, and then cleared again by various things that change attributes. It seems to fast-path some security checks. According to git annotate of Al Viro added it in commit 9e1f1de0 the description of which boils down to "found another way in which NFS sucks, try to work around it". (By the way, MS_RELATIME as supplied from userspace is a complete NOP. Read do_mount() if you don't believe me: it's never used before it's cleared.) Anyway, it might be a good janitor project to zap these in do_mount and then grep for the various redundant clearing of them elsewhere, and clean up the duplication. (I realize not a lot of people ever write mount implementations, but this is the second time _I've_ done it, and there's still no documentation on this, which means I need to write some...) Rob -- GNU/Linux isn't: Linux=GPLv2, GNU=GPLv3+, they can't share code. Either it's "mere aggregation", or a license violation. Pick one. -- To unsubscribe from this list: send the line "unsubscribe kernel-janitors" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
