diff options
Diffstat (limited to 'include/block/block.h')
| -rw-r--r-- | include/block/block.h | 35 |
1 files changed, 19 insertions, 16 deletions
diff --git a/include/block/block.h b/include/block/block.h index 90932b4709..9b355e92d8 100644 --- a/include/block/block.h +++ b/include/block/block.h @@ -121,29 +121,32 @@ typedef struct HDGeometry { #define BDRV_REQUEST_MAX_BYTES (BDRV_REQUEST_MAX_SECTORS << BDRV_SECTOR_BITS) /* - * Allocation status flags - * BDRV_BLOCK_DATA: data is read from a file returned by bdrv_get_block_status. - * BDRV_BLOCK_ZERO: sectors read as zero - * BDRV_BLOCK_OFFSET_VALID: sector stored as raw data in a file returned by - * bdrv_get_block_status. + * Allocation status flags for bdrv_get_block_status() and friends. + * + * Public flags: + * BDRV_BLOCK_DATA: allocation for data at offset is tied to this layer + * BDRV_BLOCK_ZERO: offset reads as zero + * BDRV_BLOCK_OFFSET_VALID: an associated offset exists for accessing raw data * BDRV_BLOCK_ALLOCATED: the content of the block is determined by this - * layer (as opposed to the backing file) - * BDRV_BLOCK_RAW: used internally to indicate that the request - * was answered by the raw driver and that one - * should look in bs->file directly. + * layer (short for DATA || ZERO), set by block layer * - * If BDRV_BLOCK_OFFSET_VALID is set, bits 9-62 represent the offset in - * bs->file where sector data can be read from as raw data. + * Internal flag: + * BDRV_BLOCK_RAW: used internally to indicate that the request was + * answered by a passthrough driver such as raw and that the + * block layer should recompute the answer from bs->file. * - * DATA == 0 && ZERO == 0 means that data is read from backing_hd if present. + * If BDRV_BLOCK_OFFSET_VALID is set, bits 9-62 (BDRV_BLOCK_OFFSET_MASK) + * represent the offset in the returned BDS that is allocated for the + * corresponding raw data; however, whether that offset actually contains + * data also depends on BDRV_BLOCK_DATA and BDRV_BLOCK_ZERO, as follows: * * DATA ZERO OFFSET_VALID - * t t t sectors read as zero, bs->file is zero at offset - * t f t sectors read as valid from bs->file at offset - * f t t sectors preallocated, read as zero, bs->file not + * t t t sectors read as zero, returned file is zero at offset + * t f t sectors read as valid from file at offset + * f t t sectors preallocated, read as zero, returned file not * necessarily zero at offset * f f t sectors preallocated but read from backing_hd, - * bs->file contains garbage at offset + * returned file contains garbage at offset * t t f sectors preallocated, read as zero, unknown offset * t f f sectors read from unknown file or offset * f t f not allocated or unknown offset, read as zero |