blkdebug: Sanity check block layer guarantees
Commits 04ed95f4 and 1a62d0ac updated the block layer to auto-fragment any I/O to fit within device boundaries. Additionally, when using a minimum alignment of 4k, we want to ensure the block layer does proper read-modify-write rather than requesting I/O on a slice of a sector. Let's enforce that the contract is obeyed when using blkdebug. For now, blkdebug only allows alignment overrides, and just inherits other limits from whatever device it is wrapping, but a future patch will further enhance things. Signed-off-by: NEric Blake <eblake@redhat.com> Reviewed-by: NKevin Wolf <kwolf@redhat.com> Reviewed-by: NMax Reitz <mreitz@redhat.com> Message-id: 20170429191419.30051-5-eblake@redhat.com Signed-off-by: NMax Reitz <mreitz@redhat.com>
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