Commit 3ef3959b authored Jul 22, 2020 by Josef Bacik Committed by David Sterba Aug 10, 2020

btrfs: don't show full path of bind mounts in subvol=



Chris Murphy reported a problem where rpm ostree will bind mount a bunch
of things for whatever voodoo it's doing.  But when it does this
/proc/mounts shows something like

  /dev/sda /mnt/test btrfs rw,relatime,subvolid=256,subvol=/foo 0 0
  /dev/sda /mnt/test/baz btrfs rw,relatime,subvolid=256,subvol=/foo/bar 0 0

Despite subvolid=256 being subvol=/foo.  This is because we're just
spitting out the dentry of the mount point, which in the case of bind
mounts is the source path for the mountpoint.  Instead we should spit
out the path to the actual subvol.  Fix this by looking up the name for
the subvolid we have mounted.  With this fix the same test looks like
this

  /dev/sda /mnt/test btrfs rw,relatime,subvolid=256,subvol=/foo 0 0
  /dev/sda /mnt/test/baz btrfs rw,relatime,subvolid=256,subvol=/foo 0 0

Reported-by: Chris Murphy <chris@colorremedies.com>
CC: stable@vger.kernel.org # 4.4+
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

parent 27942c99

fs/btrfs/super.c

+8 −2

Original line number	Diff line number	Diff line
		@@ -1386,6 +1386,7 @@ static int btrfs_show_options(struct seq_file seq, struct dentry dentry)
		{
		struct btrfs_fs_info *info = btrfs_sb(dentry->d_sb);
		const char *compress_type;
		const char *subvol_name;

		if (btrfs_test_opt(info, DEGRADED))
		seq_puts(seq, ",degraded");
		@@ -1472,8 +1473,13 @@ static int btrfs_show_options(struct seq_file seq, struct dentry dentry)
		seq_puts(seq, ",ref_verify");
		seq_printf(seq, ",subvolid=%llu",
		BTRFS_I(d_inode(dentry))->root->root_key.objectid);
		subvol_name = btrfs_get_subvol_name_from_objectid(info,
		BTRFS_I(d_inode(dentry))->root->root_key.objectid);
		if (!IS_ERR(subvol_name)) {
		seq_puts(seq, ",subvol=");
		seq_dentry(seq, dentry, " \t\n\\");
		seq_escape(seq, subvol_name, " \t\n\\");
		kfree(subvol_name);
		}
		return 0;
		}

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