Enhance the driver to handle whatever maximum segment number the host
tells us to handle. Do to this, we need to allocate the scatterlist
dynamically.
We set max_phys_segments and max_hw_segments to the same value (1 if
the host doesn't tell us, since that's safest and all known hosts do
tell us).
Note that kmalloc'ing the structure for large sg_elems might be
problematic: the fix for this is sg_table, but that requires more
work.
Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
diff -r 177219c4da07 drivers/block/virtio_blk.c
--- a/drivers/block/virtio_blk.c Mon Nov 17 17:16:35 2008 +1030
+++ b/drivers/block/virtio_blk.c Mon Nov 17 17:16:41 2008 +1030
@@ -6,7 +6,6 @@
#include <linux/virtio_blk.h>
#include <linux/scatterlist.h>
-#define VIRTIO_MAX_SG (3+MAX_PHYS_SEGMENTS)
#define PART_BITS 4
static int major, index;
@@ -26,8 +25,11 @@
mempool_t *pool;
+ /* What host tells us, plus 2 for header & tailer. */
+ unsigned int sg_elems;
+
/* Scatterlist: can be too big for stack. */
- struct scatterlist sg[VIRTIO_MAX_SG];
+ struct scatterlist sg[/*sg_elems*/];
};
struct virtblk_req
@@ -97,8 +99,6 @@
if (blk_barrier_rq(vbr->req))
vbr->out_hdr.type |= VIRTIO_BLK_T_BARRIER;
- /* This init could be done at vblk creation time */
- sg_init_table(vblk->sg, VIRTIO_MAX_SG);
sg_set_buf(&vblk->sg[0], &vbr->out_hdr, sizeof(vbr->out_hdr));
num = blk_rq_map_sg(q, vbr->req, vblk->sg+1);
sg_set_buf(&vblk->sg[num+1], &vbr->status, sizeof(vbr->status));
@@ -130,7 +130,7 @@
while ((req = elv_next_request(q)) != NULL) {
vblk = req->rq_disk->private_data;
- BUG_ON(req->nr_phys_segments > ARRAY_SIZE(vblk->sg));
+ BUG_ON(req->nr_phys_segments + 2 > vblk->sg_elems);
/* If this request fails, stop queue and wait for something to
finish to restart it. */
@@ -196,12 +196,22 @@
int err;
u64 cap;
u32 v;
- u32 blk_size;
+ u32 blk_size, sg_elems;
if (index_to_minor(index) >= 1 << MINORBITS)
return -ENOSPC;
- vdev->priv = vblk = kmalloc(sizeof(*vblk), GFP_KERNEL);
+ /* We need to know how many segments before we allocate. */
+ err = virtio_config_val(vdev, VIRTIO_BLK_F_SEG_MAX,
+ offsetof(struct virtio_blk_config, seg_max),
+ &sg_elems);
+ if (err)
+ sg_elems = 1;
+
+ /* We need an extra sg elements at head and tail. */
+ sg_elems += 2;
+ vdev->priv = vblk = kmalloc(sizeof(*vblk) +
+ sizeof(vblk->sg[0]) * sg_elems, GFP_KERNEL);
if (!vblk) {
err = -ENOMEM;
goto out;
@@ -210,6 +220,8 @@
INIT_LIST_HEAD(&vblk->reqs);
spin_lock_init(&vblk->lock);
vblk->vdev = vdev;
+ vblk->sg_elems = sg_elems;
+ sg_init_table(vblk->sg, vblk->sg_elems);
/* We expect one virtqueue, for output. */
vblk->vq = vdev->config->find_vq(vdev, 0, blk_done);
@@ -277,6 +289,10 @@
}
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);
+
/* No real sector limit. */
blk_queue_max_sectors(vblk->disk->queue, -1U);
@@ -289,12 +305,6 @@
blk_queue_max_segment_size(vblk->disk->queue, v);
else
blk_queue_max_segment_size(vblk->disk->queue, -1UL);
-
- err = virtio_config_val(vdev, VIRTIO_BLK_F_SEG_MAX,
- offsetof(struct virtio_blk_config, seg_max),
- &v);
- if (!err)
- blk_queue_max_hw_segments(vblk->disk->queue, v);
/* Host can optionally specify the block size of the device */
err = virtio_config_val(vdev, VIRTIO_BLK_F_BLK_SIZE,
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