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From: Christoph Hellwig on 29 Jan 2010 14:10
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(a)lst.de>

Index: linux-2.6/drivers/block/virtio_blk.c
===================================================================
--- linux-2.6.orig/drivers/block/virtio_blk.c 2010-01-29 11:13:38.509004113 +0100
+++ linux-2.6/drivers/block/virtio_blk.c 2010-01-29 19:36:44.183006458 +0100
@@ -243,10 +243,12 @@ static int index_to_minor(int index)
static int __devinit virtblk_probe(struct virtio_device *vdev)
{
struct virtio_blk *vblk;
+ struct request_queue *q;
int err;
u64 cap;
u32 v, blk_size, sg_elems, opt_io_size;
u16 min_io_size;
+ u8 physical_block_exp, alignment_offset;

if (index_to_minor(index) >= 1 << MINORBITS)
return -ENOSPC;
@@ -293,13 +295,13 @@ static int __devinit virtblk_probe(struc
goto out_mempool;
}

- vblk->disk->queue = blk_init_queue(do_virtblk_request, &vblk->lock);
- if (!vblk->disk->queue) {
+ q = vblk->disk->queue = blk_init_queue(do_virtblk_request, &vblk->lock);
+ if (!q) {
err = -ENOMEM;
goto out_put_disk;
}

- vblk->disk->queue->queuedata = vblk;
+ q->queuedata = vblk;

if (index < 26) {
sprintf(vblk->disk->disk_name, "vd%c", 'a' + index % 26);
@@ -323,10 +325,10 @@ static int __devinit virtblk_probe(struc

/* If barriers are supported, tell block layer that queue is ordered */
if (virtio_has_feature(vdev, VIRTIO_BLK_F_FLUSH))
- blk_queue_ordered(vblk->disk->queue, QUEUE_ORDERED_DRAIN_FLUSH,
+ blk_queue_ordered(q, QUEUE_ORDERED_DRAIN_FLUSH,
virtblk_prepare_flush);
else if (virtio_has_feature(vdev, VIRTIO_BLK_F_BARRIER))
- blk_queue_ordered(vblk->disk->queue, QUEUE_ORDERED_TAG, NULL);
+ blk_queue_ordered(q, QUEUE_ORDERED_TAG, NULL);

/* If disk is read-only in the host, the guest should obey */
if (virtio_has_feature(vdev, VIRTIO_BLK_F_RO))
@@ -345,14 +347,14 @@ static int __devinit virtblk_probe(struc
set_capacity(vblk->disk, cap);

/* We can handle whatever the host told us to handle. */
- blk_queue_max_phys_segments(vblk->disk->queue, vblk->sg_elems-2);
- blk_queue_max_hw_segments(vblk->disk->queue, vblk->sg_elems-2);
+ blk_queue_max_phys_segments(q, vblk->sg_elems-2);
+ blk_queue_max_hw_segments(q, vblk->sg_elems-2);

/* No need to bounce any requests */
- blk_queue_bounce_limit(vblk->disk->queue, BLK_BOUNCE_ANY);
+ blk_queue_bounce_limit(q, BLK_BOUNCE_ANY);

/* No real sector limit. */
- blk_queue_max_sectors(vblk->disk->queue, -1U);
+ blk_queue_max_sectors(q, -1U);

/* Host can optionally specify maximum segment size and number of
* segments. */
@@ -360,29 +362,46 @@ static int __devinit virtblk_probe(struc
offsetof(struct virtio_blk_config, size_max),
&v);
if (!err)
- blk_queue_max_segment_size(vblk->disk->queue, v);
+ blk_queue_max_segment_size(q, v);
else
- blk_queue_max_segment_size(vblk->disk->queue, -1U);
+ blk_queue_max_segment_size(q, -1U);

/* Host can optionally specify the block size of the device */
err = virtio_config_val(vdev, VIRTIO_BLK_F_BLK_SIZE,
offsetof(struct virtio_blk_config, blk_size),
&blk_size);
if (!err)
- blk_queue_logical_block_size(vblk->disk->queue, blk_size);
+ blk_queue_logical_block_size(q, blk_size);

/* Use topology information if available */
- err = virtio_config_val(vdev, VIRTIO_BLK_F_BLK_TOPOLOGY,
+ err = virtio_config_val(vdev, VIRTIO_BLK_F_TOPOLOGY,
+ offsetof(struct virtio_blk_config, physical_block_exp),
+ &physical_block_exp);
+ if (!err && physical_block_exp) {
+ u16 physical_block_size =
+ queue_logical_block_size(q) * (1 << physical_block_exp);
+ blk_queue_physical_block_size(q, physical_block_size);
+ }
+
+ err = virtio_config_val(vdev, VIRTIO_BLK_F_TOPOLOGY,
+ offsetof(struct virtio_blk_config, alignment_offset),
+ &alignment_offset);
+ if (!err && alignment_offset) {
+ u16 alignment = queue_logical_block_size(q) * alignment_offset;
+ blk_queue_alignment_offset(q, alignment);
+ }
+
+ err = virtio_config_val(vdev, VIRTIO_BLK_F_TOPOLOGY,
offsetof(struct virtio_blk_config, min_io_size),
&min_io_size);
- if (!err)
- blk_queue_io_min(vblk->disk->queue, min_io_size);
+ if (!err && min_io_size)
+ blk_queue_io_min(q, min_io_size);

- err = virtio_config_val(vdev, VIRTIO_BLK_F_BLK_TOPOLOGY,
+ err = virtio_config_val(vdev, VIRTIO_BLK_F_TOPOLOGY,
offsetof(struct virtio_blk_config, opt_io_size),
&opt_io_size);
- if (!err)
- blk_queue_io_opt(vblk->disk->queue, opt_io_size);
+ if (!err && opt_io_size)
+ blk_queue_io_opt(q, opt_io_size);


add_disk(vblk->disk);
Index: linux-2.6/include/linux/virtio_blk.h
===================================================================
--- linux-2.6.orig/include/linux/virtio_blk.h 2010-01-29 11:11:20.436254184 +0100
+++ linux-2.6/include/linux/virtio_blk.h 2010-01-29 19:35:44.431016843 +0100
@@ -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 covered 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 bytes. */
+ __u16 min_io_size;
+ /* optimal sustained I/O size. */
+ __u32 opt_io_size;
+
} __attribute__((packed));

/*
--
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Prev: 2.6.32 stalls as guest in virtualbox
Next: [patch 1/2] x86, irq: update the vector domain for legacy irqs handled by io-apic