Check for COW space before writing to COW
This gives a more detailed message when we run out of cow space.
Also, previously, it's possible that the COW op metadata writes
successfully but op data fails due to out of space, resulting in a
broken COW image. After this change, we won't write anything unless
there's sufficient space for both OP metadata and block data. This makes
COW operations more atomic and easier to debug/inspect.
Test: th
Change-Id: I6c1347e91b4ec2d7e434b47a0f47b290e288e600
2 files changed
