btrfs: check type flags in alloc_ordered_extent()

btrfs: check type flags in alloc_ordered_extent()

Unlike other flags used in btrfs, BTRFS_ORDERED_* macros are different as
they cannot be directly used as flags.

They are defined as bit values, thus they should be utilized with
bit operations, not directly with logical operations.

Unfortunately sometimes I forgot this and passed the incorrect flags
to alloc_ordered_extent() and hit weird bugs.

Enhance the type checks in alloc_ordered_extent():

- Make sure there is one and only one bit set for exclusive type flags
  There are four exclusive type flags, REGULAR, NOCOW, PREALLOC and
  COMPRESSED.
  So introduce a new macro, BTRFS_ORDERED_EXCLUSIVE_FLAGS, to cover
  above flags.

  Add an ASSERT() to check one and only one of those exclusive flags can
  be set for alloc_ordered_extent().

- Re-order the type bit numbers to the end of the enum
  This is make it much harder to get a valid false negative.

  E.g., with the old code BTRFS_ORDERED_REGULAR starts at zero, we can
  have the following flags passing the bit uniqueness check:

  * BTRFS_ORDERED_NOCOW
    Be treated as BTRFS_ORDERED_REGULAR (1 == 1UL << 0).

  * BTRFS_ORDERED_PREALLOC
    Be treated as BTRFS_ORDERED_NOCOW (2 == 1UL << 1).

  * BTRFS_ORDERED_DIRECT
    Be treated as BTRFS_ORDERED_PREALLOC (4 == 1UL << 2).

  Now all those types start at 8, passing any of those bit numbers as
  flags directly will not pass the ASSERT().

- Add a static assert to avoid overflow
  To make sure all BTRFS_ORDERED_* flags can fit into an unsigned long.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>