diff options
| -rw-r--r-- | fs/namespace.c | 54 | ||||
| -rw-r--r-- | include/linux/mount.h | 3 |
2 files changed, 57 insertions, 0 deletions
diff --git a/fs/namespace.c b/fs/namespace.c index 94f026ec990..066b393578c 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -80,6 +80,60 @@ struct vfsmount *alloc_vfsmnt(const char *name) return mnt; } +/* + * Most r/o checks on a fs are for operations that take + * discrete amounts of time, like a write() or unlink(). + * We must keep track of when those operations start + * (for permission checks) and when they end, so that + * we can determine when writes are able to occur to + * a filesystem. + */ +/** + * mnt_want_write - get write access to a mount + * @mnt: the mount on which to take a write + * + * This tells the low-level filesystem that a write is + * about to be performed to it, and makes sure that + * writes are allowed before returning success. When + * the write operation is finished, mnt_drop_write() + * must be called. This is effectively a refcount. + */ +int mnt_want_write(struct vfsmount *mnt) +{ + if (__mnt_is_readonly(mnt)) + return -EROFS; + return 0; +} +EXPORT_SYMBOL_GPL(mnt_want_write); + +/** + * mnt_drop_write - give up write access to a mount + * @mnt: the mount on which to give up write access + * + * Tells the low-level filesystem that we are done + * performing writes to it. Must be matched with + * mnt_want_write() call above. + */ +void mnt_drop_write(struct vfsmount *mnt) +{ +} +EXPORT_SYMBOL_GPL(mnt_drop_write); + +/* + * __mnt_is_readonly: check whether a mount is read-only + * @mnt: the mount to check for its write status + * + * This shouldn't be used directly ouside of the VFS. + * It does not guarantee that the filesystem will stay + * r/w, just that it is right *now*. This can not and + * should not be used in place of IS_RDONLY(inode). + */ +int __mnt_is_readonly(struct vfsmount *mnt) +{ + return (mnt->mnt_sb->s_flags & MS_RDONLY); +} +EXPORT_SYMBOL_GPL(__mnt_is_readonly); + int simple_set_mnt(struct vfsmount *mnt, struct super_block *sb) { mnt->mnt_sb = sb; diff --git a/include/linux/mount.h b/include/linux/mount.h index 5ee2df217cd..2eecd2c8c76 100644 --- a/include/linux/mount.h +++ b/include/linux/mount.h @@ -71,9 +71,12 @@ static inline struct vfsmount *mntget(struct vfsmount *mnt) return mnt; } +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); +extern int __mnt_is_readonly(struct vfsmount *mnt); static inline void mntput(struct vfsmount *mnt) { |