diff options
Diffstat (limited to 'include/block/block_int.h')
| -rw-r--r-- | include/block/block_int.h | 12 |
1 files changed, 11 insertions, 1 deletions
diff --git a/include/block/block_int.h b/include/block/block_int.h index 1b86b59af1..3d6cf88592 100644 --- a/include/block/block_int.h +++ b/include/block/block_int.h @@ -123,7 +123,17 @@ struct BlockDriver { */ bool bdrv_needs_filename; - /* Set if a driver can support backing files */ + /* + * Set if a driver can support backing files. This also implies the + * following semantics: + * + * - Return status 0 of .bdrv_co_block_status means that corresponding + * blocks are not allocated in this layer of backing-chain + * - For such (unallocated) blocks, read will: + * - fill buffer with zeros if there is no backing file + * - read from the backing file otherwise, where the block layer + * takes care of reading zeros beyond EOF if backing file is short + */ bool supports_backing; /* For handling image reopen for split or non-split files */ |