For reads and writes, the sector is the offset divided by 512, not multiplied. For everything else, it is zero. Mention VIRTIO_BLK_F_BLK_SIZE in the normative section. The data length need not be a multiple of 512, so do not express that requirement in the virtio_blk_req struct. Signed-off-by: Paolo Bonzini <> --- content.tex
12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/content.tex b/content.tex index fd3a3c2..b7d0bea 100644 --- a/content.tex +++ b/content.tex @@ -3711,7 +3711,7 @@ struct virtio_blk_req {
le32 type;
le32 reserved;
le64 sector; -
u8 data[][512]; +
u8 data[];
u8 status; };
@@ -3737,7 +3737,7 @@ The type of the request is either a read (VIRTIO_BLK_T_IN), a write #define VIRTIO_BLK_T_WRITE_ZEROES 13 end{lstlisting}
-The field{sector} number indicates the offset (multiplied by 512) where +The field{sector} number indicates the offset (in 512-byte units) where the read or write is to occur. This field is unused and set to 0 for commands other than read or write.
@@ -3766,9 +3766,15 @@ A driver SHOULD NOT submit a request which has more than field{seg_max} descriptors in the data portion, or which has more than field{size_max} bytes in a single descriptor in the data portion.
+The byte offset of each operation (sector number multiplied by +512) and data length SHOULD be aligned to the block size if the +VIRTIO_BLK_F_BLK_SIZE feature is negotiated. + A driver SHOULD accept the VIRTIO_BLK_F_RO feature if offered.
-A driver MUST set field{sector} to 0 for a VIRTIO_BLK_T_FLUSH request. +A driver MUST set field{sector} to 0 for a VIRTIO_BLK_T_FLUSH, +VIRTIO_BLK_T_DISCARD or VIRTIO_BLK_T_WRITE_ZEROES request. + A driver SHOULD NOT include any data in a VIRTIO_BLK_T_FLUSH request.
If the VIRTIO_BLK_F_CONFIG_WCE feature is negotiated, the driver MAY -- 2.17.1
