Current QEMU and Linux drivers can export queue parameters via the
virtio-blk configuration space. Document this, since the next patch
will have to add another configuration field after these.
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
virtio-spec.lyx | 85 +++++++++++++++++++++++++++++++++++++++++++++++++++----
1 file changed, 80 insertions(+), 5 deletions(-)
diff --git a/virtio-spec.lyx b/virtio-spec.lyx
index dd2d53b..859dbe7 100644
--- a/virtio-spec.lyx
+++ b/virtio-spec.lyx
@@ -5021,7 +5021,20 @@ VIRTIO_BLK_F_SCSI (7) Device supports scsi packet commands.
\end_layout
\begin_layout Description
-VIRTIO_BLK_F_FLUSH (9) Cache flush command support.Device
+VIRTIO_BLK_F_FLUSH (9) Cache flush command support.
+\change_inserted 1531152142 1341305427
+
+\end_layout
+
+\begin_layout Description
+
+\change_inserted 1531152142 1341301882
+VIRTIO_BLK_F_TOPOLOGY (10) Device exports information on optimal I/O alignment.
+\end_layout
+
+\end_deeper
+\begin_layout Description
+Device
\begin_inset space ~
\end_inset
@@ -5090,6 +5103,48 @@ struct virtio_blk_config {
\begin_layout Plain Layout
+\change_inserted 1531152142 1341301807
+
+ struct virtio_blk_topology {
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 1531152142 1341301810
+
+ u8 physical_block_exp;
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 1531152142 1341301817
+
+ u8 alignment_offset;
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 1531152142 1341301822
+
+ u16 min_io_size;
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 1531152142 1341301827
+
+ u32 opt_io_size;
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 1531152142 1341301911
+
+ } topology;
+\end_layout
+
+\begin_layout Plain Layout
+
};
\end_layout
@@ -5098,7 +5153,6 @@ struct virtio_blk_config {
\end_layout
-\end_deeper
\begin_layout Section*
Device Initialization
\end_layout
@@ -5119,15 +5173,36 @@ capacity
\begin_layout Enumerate
If the VIRTIO_BLK_F_BLK_SIZE feature is negotiated, the blk_size field can
be read to determine the optimal sector size for the driver to use.
- This does not effect the units used in the protocol (always 512 bytes),
- but awareness of the correct value can effect performance.
+ This does not
+\change_deleted 1531152142 1341301967
+e
+\change_inserted 1531152142 1341301967
+a
+\change_unchanged
+ffect the units used in the protocol (always 512 bytes), but awareness of
+ the correct value can
+\change_deleted 1531152142 1341301978
+e
+\change_inserted 1531152142 1341301978
+a
+\change_unchanged
+ffect performance.
\end_layout
\begin_layout Enumerate
If the VIRTIO_BLK_F_RO feature is set by the device, any write requests
will fail.
-\change_inserted 1531152142 1341301982
+\change_inserted 1531152142 1341301920
+
+\end_layout
+\begin_layout Enumerate
+
+\change_inserted 1531152142 1341301982
+If the VIRTIO_BLK_F_TOPOLOGY feature is negotiated, the fields in the topology
+ struct can be read to determine the physical block size and optimal I/O
+ lengths for the driver to use.
+ This also does not affect the units in the protocol, only performance.
\end_layout
\begin_layout Section*
--
1.7.10.2
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