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SubjectRe: [PATCH 2/3] Btrfs: unify subvol= and subvolid= mounting
On Tue, Apr 07, 2015 at 10:34:01PM -0700, Omar Sandoval wrote:
> Currently, mounting a subvolume with subvolid= takes a different code
> path than mounting with subvol=. This isn't really a big deal except for
> the fact that mounts done with subvolid= or the default subvolume don't
> have a dentry that's connected to the dentry tree like in the subvol=
> case. To unify the code paths, when given subvolid= or using the default
> subvolume ID, translate it into a subvolume name by walking
> ROOT_BACKREFs in the root tree and INODE_REFs in the filesystem trees.

Can you please split this patches? It's doing several things, but the
core change will probably be a big one. The mount path is not trivial,
all the recursions and argument replacements.

Otherwise, I'm ok with this approach, ie. to set up the dentry at mount
time.

A few comments below.

> /*
> - * This will strip out the subvol=%s argument for an argument string and add
> - * subvolid=0 to make sure we get the actual tree root for path walking to the
> - * subvol we want.
> + * This will add subvolid=0 to the argument string while removing any subvol=
> + * and subvolid= arguments to make sure we get the top-level root for path
> + * walking to the subvol we want.
> */
> static char *setup_root_args(char *args)
> {
> - unsigned len = strlen(args) + 2 + 1;
> - char *src, *dst, *buf;
> -
> - /*
> - * We need the same args as before, but with this substitution:
> - * s!subvol=[^,]+!subvolid=0!
> - *
> - * Since the replacement string is up to 2 bytes longer than the
> - * original, allocate strlen(args) + 2 + 1 bytes.
> - */
> + char *p, *dst, *buf;

Fix the coding style.

> root = mount_subtree(mnt, subvol_name);
> + mnt = NULL; /* mount_subtree drops our reference on the vfsmount. */

Put the comment on a separate line.

> + if (!IS_ERR(root) && subvol_objectid &&
> + BTRFS_I(root->d_inode)->root->root_key.objectid != subvol_objectid) {
> + pr_warn("BTRFS: subvol '%s' does not match subvolid %llu\n",
> + subvol_name, subvol_objectid);

We should define the precedence of subvolid and subvol if both are set.
A warning might not be enough.


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