btrfs-progs: canonicalize pathnames for device commands

mount(8) will canonicalize pathnames before passing them to the kernel.
Links to e.g. /dev/sda will be resolved to /dev/sda. Links to /dev/dm-#
will be resolved using the name of the device mapper table to
/dev/mapper/<name>.

Btrfs will use whatever name the user passes to it, regardless of whether
it is canonical or not. That means that if a 'btrfs device ready' is
issued on any device node pointing to the original device, it will adopt
the new name instead of the name that was used during mount.

Mounting using /dev/sdb2 will result in df:
/dev/sdb2      209715200 39328 207577088   1% /mnt

lrwxrwxrwx 1 root root 4 Jun  4 13:36 /dev/whatever-i-like -> sdb2
/dev/whatever-i-like 209715200 39328 207577088   1% /mnt

Likewise, mounting with /dev/mapper/whatever and using /dev/dm-0 with a
btrfs device command results in df showing /dev/dm-0. This can happen with
multipath devices with friendly names enabled and doing something like
'partprobe' which (at least with our version) ends up issuing a 'change'
uevent on the sysfs node. That *always* uses the dm-# name, and we get
confused users.

This patch does the same canonicalization of the paths that mount does
so that we don't end up having inconsistent names reported by ->show_devices
later.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
[use PATH_MAX in canonicalize_dm_name]
Signed-off-by: David Sterba <dsterba@suse.cz>

1 files changed, 2 insertions, 0 deletions

diff --git a/utils.h b/utils.h
index 4cfd315a..37fe1ba0 100644
--- a/utils.h
+++ b/utils.h
@@ -53,6 +53,8 @@ int btrfs_add_to_fsid(struct btrfs_trans_handle *trans,
 int btrfs_scan_for_fsid(int run_ioctls);
 void btrfs_register_one_device(char *fname);
 int btrfs_scan_one_dir(char *dirname, int run_ioctl);
+char *canonicalize_dm_name(const char *ptname);
+char *canonicalize_path(const char *path);
 int check_mounted(const char *devicename);
 int check_mounted_where(int fd, const char *file, char *where, int size,
 			struct btrfs_fs_devices **fs_devices_mnt);