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Subject[RFC][PATCH 1/2] pin kern mounts as writable
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If we are going to continue to use mnt_clone_write() inside
of init_file(), then we're going to need some kind of extra
handling.

What I want to do in the next patch is add a debugging check
in mnt_clone_write() to double-check that there *is* a real
writer on the mount before mnt_clone_write() succeeds. To
do that, we either need to check for MS_KERNMOUNT around
that debug check, or we need to make sure that these kern
mounts *have* a write already.

I'm choosing to make sure they always have a write.

---

linux-2.6.git-dave/fs/super.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)

diff -puN fs/super.c~pin-mnt-writable fs/super.c
--- linux-2.6.git/fs/super.c~pin-mnt-writable 2009-08-03 14:47:29.000000000 -0700
+++ linux-2.6.git-dave/fs/super.c 2009-08-03 14:49:49.000000000 -0700
@@ -948,7 +948,19 @@ EXPORT_SYMBOL_GPL(do_kern_mount);

struct vfsmount *kern_mount_data(struct file_system_type *type, void *data)
{
- return vfs_kern_mount(type, MS_KERNMOUNT, type->name, data);
+ int err = 0;
+ struct vfsmount *mnt;
+ mnt = vfs_kern_mount(type, MS_KERNMOUNT, type->name, data);
+ if (IS_ERR(mnt))
+ return mnt;
+ /*
+ * We will never allow this mount to be r/o. Doing
+ * this makes it explicit and allows mnt_clone_write()
+ * to be used unconditionally on this mount.
+ */
+ err = mnt_want_write(mnt);
+ WARN_ON(err);
+ return mnt;
}

EXPORT_SYMBOL_GPL(kern_mount_data);
diff -puN include/linux/mount.h~pin-mnt-writable include/linux/mount.h
_

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