virtio_blk: add block topology support

Allow reading various alignment values from the config page.  This
allows the guest to much better align I/O requests depending on the
storage topology.

Note that the formats for the config values appear a bit messed up,
but we follow the formats used by ATA and SCSI so they are expected in
the storage world.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 13 insertions, 0 deletions

diff --git a/include/linux/virtio_blk.h b/include/linux/virtio_blk.h
index fd294c56d571..e52029e98919 100644
--- a/include/linux/virtio_blk.h
+++ b/include/linux/virtio_blk.h
@@ -15,6 +15,7 @@
 #define VIRTIO_BLK_F_BLK_SIZE   6       /* Block size of disk is available*/
 #define VIRTIO_BLK_F_SCSI       7       /* Supports scsi command passthru */
 #define VIRTIO_BLK_F_FLUSH      9       /* Cache flush command support */
+#define VIRTIO_BLK_F_TOPOLOGY   10      /* Topology information is available */
 
 struct virtio_blk_config {
         /* The capacity (in 512-byte sectors). */
@@ -29,8 +30,20 @@ struct virtio_blk_config {
                 __u8 heads;
                 __u8 sectors;
         } geometry;
+
         /* block size of device (if VIRTIO_BLK_F_BLK_SIZE) */
         __u32 blk_size;
+
+        /* the next 4 entries are guarded by VIRTIO_BLK_F_TOPOLOGY  */
+        /* exponent for physical block per logical block. */
+        __u8 physical_block_exp;
+        /* alignment offset in logical blocks. */
+        __u8 alignment_offset;
+        /* minimum I/O size without performance penalty in logical blocks. */
+        __u16 min_io_size;
+        /* optimal sustained I/O size in logical blocks. */
+        __u32 opt_io_size;
+
 } __attribute__((packed));
 
 /*