On Tue, 2010-01-26 at 14:20 -0500, Valerie Aurora wrote:
> Al, you might have already fixed this as part of your mount flag
> rewrite, but here's a patch to clean up some problems with shared
> mount flag propagation that I ran into while working on union mounts.
> Against 2.6.32.
>
> -VAL
>
> commit 3f436c4466f278900d451494b317f6bb80b4c24b
> Author: Valerie Aurora <vaurora@xxxxxxxxxx>
> Date: Tue Jan 26 11:09:00 2010 -0800
>
> VFS: Clean up shared mount flag propagation
>
> The handling of mount flags in set_mnt_shared() got a little tangled
> up during previous cleanups, with the following problems:
>
> * MNT_PNODE_MASK is defined as a literal constant when it should be a
> bitwise xor of other MNT_* flags
> * set_mnt_shared() clears and then sets MNT_SHARED (part of MNT_PNODE_MASK)
> * MNT_PNODE_MASK could use a comment in mount.h
> * MNT_PNODE_MASK is a terrible name, change to MNT_SHARED_MASK
>
> This patch fixes these problems.
>
> diff --git a/fs/pnode.h b/fs/pnode.h
> index 958665d..adc52ca 100644
> --- a/fs/pnode.h
> +++ b/fs/pnode.h
> @@ -26,7 +26,7 @@
>
> static inline void set_mnt_shared(struct vfsmount *mnt)
> {
> - mnt->mnt_flags &= ~MNT_PNODE_MASK;
> + mnt->mnt_flags &= ~MNT_SHARED_MASK;
> mnt->mnt_flags |= MNT_SHARED;
> }
>
Is resetting the MNT_SHARED bit and setting it back, causing a issue?
If so, why not just do
- mnt->mnt_flags &= ~MNT_PNODE_MASK;
+ mnt->mnt_flags &= ~MNT_UNBINDABLE;
> diff --git a/include/linux/mount.h b/include/linux/mount.h
> index 5d52753..257985f 100644
> --- a/include/linux/mount.h
> +++ b/include/linux/mount.h
> @@ -34,7 +34,15 @@ struct mnt_namespace;
>
> #define MNT_SHARED 0x1000 /* if the vfsmount is a shared mount */
> #define MNT_UNBINDABLE 0x2000 /* if the vfsmount is a unbindable mount */
> -#define MNT_PNODE_MASK 0x3000 /* propagation flag mask */
I prefer to leave the name MNT_PNODE_MASK as is, because it captures the
notion of propagation v/s the notion of just being shared.
> +/*
> + * MNT_SHARED_MASK is the set of flags that should be cleared when a
> + * mount becomes shared. Currently, this is only the flag that says a
> + * mount cannot be bind mounted, since this is how we create a mount
> + * that shares events with another mount. If you add a new MNT_*
> + * flag, consider how it interacts with shared mounts.
> + */
> +#define MNT_SHARED_MASK (MNT_UNBINDABLE)
and make this
+#define MNT_SHARED_MASK (MNT_UNBINDABLE | MNT_SHARED)
RP
> +
>
> struct vfsmount {
> struct list_head mnt_hash;
--
Ram Pai
System X Device-Driver Enablement Lead
Linux Technology Center
Beaverton OR-97006
503-5783752 t/l 7753752
linuxram@xxxxxxxxxx
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