The patch titled
r/o bind mounts: stub functions
has been added to the -mm tree. Its filename is
r-o-bind-mounts-stub-functions.patch
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------------------------------------------------------
Subject: r/o bind mounts: stub functions
From: Dave Hansen <haveblue@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.
Acked-by: Serge Hallyn <serue@xxxxxxxxxx>
Acked-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Dave Hansen <haveblue@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/namespace.c | 54 ++++++++++++++++++++++++++++++++++++++++
include/linux/mount.h | 3 ++
2 files changed, 57 insertions(+)
diff -puN fs/namespace.c~r-o-bind-mounts-stub-functions fs/namespace.c
--- a/fs/namespace.c~r-o-bind-mounts-stub-functions
+++ a/fs/namespace.c
@@ -80,6 +80,60 @@ struct vfsmount *alloc_vfsmnt(const char
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 -puN include/linux/mount.h~r-o-bind-mounts-stub-functions include/linux/mount.h
--- a/include/linux/mount.h~r-o-bind-mounts-stub-functions
+++ a/include/linux/mount.h
@@ -70,9 +70,12 @@ static inline struct vfsmount *mntget(st
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)
{
_
Patches currently in -mm which might be from haveblue@xxxxxxxxxx are
enable-hotplug-memory-remove-for-ppc64.patch
reiserfs-eliminate-private-use-of-struct-file-in-xattr.patch
hppfs-pass-vfsmount-to-dentry_open.patch
check-for-null-vfsmount-in-dentry_open.patch
fix-up-new-filp-allocators.patch
do-namei_flags-calculation-inside-open_namei.patch
merge-open_namei-and-do_filp_open.patch
r-o-bind-mounts-stub-functions.patch
r-o-bind-mounts-create-helper-to-drop-file-write-access.patch
r-o-bind-mounts-drop-write-during-emergency-remount.patch
r-o-bind-mounts-elevate-write-count-for-vfs_rmdir.patch
r-o-bind-mounts-elevate-write-count-for-callers-of-vfs_mkdir.patch
r-o-bind-mounts-elevate-mnt_writers-for-unlink-callers.patch
r-o-bind-mounts-elevate-write-count-for-xattr_permission-callers.patch
r-o-bind-mounts-elevate-write-count-for-ncp_ioctl.patch
r-o-bind-mounts-write-counts-for-time-functions.patch
r-o-bind-mounts-elevate-write-count-for-do_utimes.patch
r-o-bind-mounts-write-count-for-file_update_time.patch
r-o-bind-mounts-write-counts-for-link-symlink.patch
r-o-bind-mounts-elevate-write-count-for-ioctls.patch
r-o-bind-mounts-elevate-write-count-for-opens.patch
r-o-bind-mounts-get-write-access-for-vfs_rename-callers.patch
r-o-bind-mounts-elevate-write-count-for-chmod-chown-callers.patch
r-o-bind-mounts-write-counts-for-truncate.patch
r-o-bind-mounts-elevate-count-for-xfs-timestamp-updates.patch
r-o-bind-mounts-make-access-use-new-r-o-helper.patch
r-o-bind-mounts-check-mnt-instead-of-superblock-directly.patch
r-o-bind-mounts-get-callers-of-vfs_mknod-create.patch
r-o-bind-mounts-track-numbers-of-writers-to-mounts.patch
r-o-bind-mounts-honor-mount-writer-counts-at-remount.patch
r-o-bind-mounts-debugging-for-missed-calls.patch
reiser4.patch
page-owner-tracking-leak-detector.patch
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