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SubjectRe: [PATCH] virtio_blk: allow re-reading config space at runtime
On Tue, Feb 01, 2011 at 08:38:27PM +0200, Michael S. Tsirkin wrote:
> Should not be hard to solve.
> If it's running, it is ok to requeue. I don't remember offhand if it's
> ok to requeue if it's queued but not running, if not we could have a
> flag that signals that's the case.

Looks like the workqueue infrastructure does indeed handle requing
an pending work_struct, and we're free to reuse it from the point
just before the callback is called.

Does the version below look okay?

---
From: Christoph Hellwig <hch@lst.de>
Subject: [PATCH v2] virtio_blk: allow re-reading config space at runtime

Wire up the virtio_driver config_changed method to get notified about
config changes raised by the host. For now we just re-read the device
size to support online resizing of devices, but once we add more
attributes that might be changeable they could be added as well.

Note that the config_changed method is called from irq context, so
we'll have to use the workqueue infrastructure to provide us a proper
user context for our changes.

Signed-off-by: Christoph Hellwig <hch@lst.de>

Index: linux-2.6/drivers/block/virtio_blk.c
===================================================================
--- linux-2.6.orig/drivers/block/virtio_blk.c 2010-12-01 09:30:59.647253809 -0700
+++ linux-2.6/drivers/block/virtio_blk.c 2011-02-01 12:10:02.803164641 -0700
@@ -6,10 +6,12 @@
#include <linux/virtio.h>
#include <linux/virtio_blk.h>
#include <linux/scatterlist.h>
+#include <linux/string_helpers.h>

#define PART_BITS 4

static int major, index;
+struct workqueue_struct *virtblk_wq;

struct virtio_blk
{
@@ -26,6 +28,9 @@ struct virtio_blk

mempool_t *pool;

+ /* Process context for config space updates */
+ struct work_struct config_work;
+
/* What host tells us, plus 2 for header & tailer. */
unsigned int sg_elems;

@@ -291,6 +296,47 @@ static ssize_t virtblk_serial_show(struc
}
DEVICE_ATTR(serial, S_IRUGO, virtblk_serial_show, NULL);

+static void virtblk_config_changed_work(struct work_struct *work)
+{
+ struct virtio_blk *vblk =
+ container_of(work, struct virtio_blk, config_work);
+ struct virtio_device *vdev = vblk->vdev;
+ struct request_queue *q = vblk->disk->queue;
+ char cap_str_2[10], cap_str_10[10];
+ u64 capacity, size;
+
+ /* Host must always specify the capacity. */
+ vdev->config->get(vdev, offsetof(struct virtio_blk_config, capacity),
+ &capacity, sizeof(capacity));
+
+ /* If capacity is too big, truncate with warning. */
+ if ((sector_t)capacity != capacity) {
+ dev_warn(&vdev->dev, "Capacity %llu too large: truncating\n",
+ (unsigned long long)capacity);
+ capacity = (sector_t)-1;
+ }
+
+ size = capacity * queue_logical_block_size(q);
+ string_get_size(size, STRING_UNITS_2, cap_str_2, sizeof(cap_str_2));
+ string_get_size(size, STRING_UNITS_10, cap_str_10, sizeof(cap_str_10));
+
+ dev_notice(&vdev->dev,
+ "new size: %llu %d-byte logical blocks (%s/%s)\n",
+ (unsigned long long)capacity,
+ queue_logical_block_size(q),
+ cap_str_10, cap_str_2);
+
+ set_capacity(vblk->disk, capacity);
+
+}
+
+static void virtblk_config_changed(struct virtio_device *vdev)
+{
+ struct virtio_blk *vblk = vdev->priv;
+
+ queue_work(virtblk_wq, &vblk->config_work);
+}
+
static int __devinit virtblk_probe(struct virtio_device *vdev)
{
struct virtio_blk *vblk;
@@ -327,6 +373,7 @@ static int __devinit virtblk_probe(struc
vblk->vdev = vdev;
vblk->sg_elems = sg_elems;
sg_init_table(vblk->sg, vblk->sg_elems);
+ INIT_WORK(&vblk->config_work, virtblk_config_changed_work);

/* We expect one virtqueue, for output. */
vblk->vq = virtio_find_single_vq(vdev, blk_done, "requests");
@@ -477,6 +524,8 @@ static void __devexit virtblk_remove(str
{
struct virtio_blk *vblk = vdev->priv;

+ flush_work(&vblk->config_work);
+
/* Nothing should be pending. */
BUG_ON(!list_empty(&vblk->reqs));

@@ -508,27 +557,47 @@ static unsigned int features[] = {
* Use __refdata to avoid this warning.
*/
static struct virtio_driver __refdata virtio_blk = {
- .feature_table = features,
- .feature_table_size = ARRAY_SIZE(features),
- .driver.name = KBUILD_MODNAME,
- .driver.owner = THIS_MODULE,
- .id_table = id_table,
- .probe = virtblk_probe,
- .remove = __devexit_p(virtblk_remove),
+ .feature_table = features,
+ .feature_table_size = ARRAY_SIZE(features),
+ .driver.name = KBUILD_MODNAME,
+ .driver.owner = THIS_MODULE,
+ .id_table = id_table,
+ .probe = virtblk_probe,
+ .remove = __devexit_p(virtblk_remove),
+ .config_changed = virtblk_config_changed,
};

static int __init init(void)
{
+ int error;
+
+ virtblk_wq = alloc_workqueue("md_misc", 0, 0);
+ if (!virtblk_wq)
+ return -ENOMEM;
+
major = register_blkdev(0, "virtblk");
- if (major < 0)
- return major;
- return register_virtio_driver(&virtio_blk);
+ if (major < 0) {
+ error = major;
+ goto out_destroy_workqueue;
+ }
+
+ error = register_virtio_driver(&virtio_blk);
+ if (error)
+ goto out_unregister_blkdev;
+ return 0;
+
+out_unregister_blkdev:
+ unregister_blkdev(major, "virtblk");
+out_destroy_workqueue:
+ destroy_workqueue(virtblk_wq);
+ return error;
}

static void __exit fini(void)
{
unregister_blkdev(major, "virtblk");
unregister_virtio_driver(&virtio_blk);
+ destroy_workqueue(virtblk_wq);
}
module_init(init);
module_exit(fini);

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