From: Dave Hansen <hansendc@xxxxxxxxxx> This patch adds two function mnt_want_write() and mnt_drop_write(). These are used like a lock pair around and fs operations that might cause a write to the filesystem. Before these can become useful, we must first cover each place in the VFS where writes are performed with a want/drop pair. When that is complete, we can actually introduce code that will safely check the counts before allowing r/w<->r/o transitions to occur. Note that we put the linux/fs.h #include as far down in mount.h as possible. This is to keep the mount.h->fs.h-> sched.h->mount.h include dependency from biting us. Signed-off-by: Dave Hansen <hansendc@xxxxxxxxxx> --- --- fs/namespace.c | 13 +++++++++++++ include/linux/mount.h | 13 +++++++++++++ 2 files changed, 26 insertions(+) Index: 2.6.22-rc4-mm2-robindmount/fs/namespace.c =================================================================== --- 2.6.22-rc4-mm2-robindmount.orig/fs/namespace.c +++ 2.6.22-rc4-mm2-robindmount/fs/namespace.c @@ -79,6 +79,19 @@ struct vfsmount *alloc_vfsmnt(const char return mnt; } +int mnt_want_write(struct vfsmount *mnt) +{ + if (__mnt_is_readonly(mnt)) + return -EROFS; + return 0; +} +EXPORT_SYMBOL_GPL(mnt_want_write); + +void mnt_drop_write(struct vfsmount *mnt) +{ +} +EXPORT_SYMBOL_GPL(mnt_drop_write); + int simple_set_mnt(struct vfsmount *mnt, struct super_block *sb) { mnt->mnt_sb = sb; Index: 2.6.22-rc4-mm2-robindmount/include/linux/mount.h =================================================================== --- 2.6.22-rc4-mm2-robindmount.orig/include/linux/mount.h +++ 2.6.22-rc4-mm2-robindmount/include/linux/mount.h @@ -74,6 +74,19 @@ static inline struct vfsmount *mntget(st return mnt; } +#include <linux/fs.h> + +/* + * This shouldn't be used directly ouside of the VFS, + * use mnt_want/drop_write() instead. + */ +static inline int __mnt_is_readonly(struct vfsmount *mnt) +{ + return (mnt->mnt_sb->s_flags & MS_RDONLY); +} + +extern int mnt_want_write(struct vfsmount *mnt); +extern void mnt_drop_write(struct vfsmount *mnt); extern void mntput_no_expire(struct vfsmount *mnt); extern void mnt_pin(struct vfsmount *mnt); extern void mnt_unpin(struct vfsmount *mnt); -- _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers