On Mon, Aug 03, 2020 at 02:37:16PM +0100, David Howells wrote:
> Add a uniquifier ID to struct mount that is effectively unique over the
> kernel lifetime to deal around mnt_id values being reused. This can then
> be exported through fsinfo() to allow detection of replacement mounts that
> happen to end up with the same mount ID.
>
> The normal mount handle is still used for referring to a particular mount.
>
> The mount notification is then changed to convey these unique mount IDs
> rather than the mount handle.
>
> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> ---
>
> fs/mount.h | 3 +++
> fs/mount_notify.c | 4 ++--
> fs/namespace.c | 3 +++
> 3 files changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/fs/mount.h b/fs/mount.h
> index 85456a5f5a3a..1037781be055 100644
> --- a/fs/mount.h
> +++ b/fs/mount.h
> @@ -79,6 +79,9 @@ struct mount {
> int mnt_expiry_mark; /* true if marked for expiry */
> struct hlist_head mnt_pins;
> struct hlist_head mnt_stuck_children;
> +#ifdef CONFIG_FSINFO
> + u64 mnt_unique_id; /* ID unique over lifetime of kernel */
> +#endif
Not sure if it's worth making conditional.
> #ifdef CONFIG_MOUNT_NOTIFICATIONS
> struct watch_list *mnt_watchers; /* Watches on dentries within this mount */
> #endif
> diff --git a/fs/mount_notify.c b/fs/mount_notify.c
> index 44f570e4cebe..d8ba66ed5f77 100644
> --- a/fs/mount_notify.c
> +++ b/fs/mount_notify.c
> @@ -90,7 +90,7 @@ void notify_mount(struct mount *trigger,
> n.watch.type = WATCH_TYPE_MOUNT_NOTIFY;
> n.watch.subtype = subtype;
> n.watch.info = info_flags | watch_sizeof(n);
> - n.triggered_on = trigger->mnt_id;
> + n.triggered_on = trigger->mnt_unique_id;
>
> switch (subtype) {
> case NOTIFY_MOUNT_EXPIRY:
> @@ -102,7 +102,7 @@ void notify_mount(struct mount *trigger,
> case NOTIFY_MOUNT_UNMOUNT:
> case NOTIFY_MOUNT_MOVE_FROM:
> case NOTIFY_MOUNT_MOVE_TO:
> - n.auxiliary_mount = aux->mnt_id;
> + n.auxiliary_mount = aux->mnt_unique_id;
Hmm, so we now have two ID's:
- one can be used to look up the mount
- one is guaranteed to be unique
With this change the mount cannot be looked up with FSINFO_FLAGS_QUERY_MOUNT,
right?
Should we be merging the two ID's into a single one which has both properties?
> break;
>
> default:
> diff --git a/fs/namespace.c b/fs/namespace.c
> index b2b9920ffd3c..1db8a64cd76f 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -115,6 +115,9 @@ static int mnt_alloc_id(struct mount *mnt)
> if (res < 0)
> return res;
> mnt->mnt_id = res;
> +#ifdef CONFIG_FSINFO
> + mnt->mnt_unique_id = atomic64_inc_return(&vfs_unique_counter);
> +#endif
> return 0;
> }
>
>
>
