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Date: Tue, 1 Feb 2011 21:51:36 +0200
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Christoph Hellwig <hch@....de>
Cc: Rusty Russell <rusty@...tcorp.com.au>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] virtio_blk: allow re-reading config space at runtime
On Tue, Feb 01, 2011 at 08:21:56PM +0100, Christoph Hellwig wrote:
> 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?
Yes, looks good to me. A couple of minor comments below
but they don't really matter. FWIW
Acked-by: Michael S. Tsirkin <mst@...hat.com>
> ---
> From: Christoph Hellwig <hch@....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@....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;
One thing to note here is that we will get this warning
on each config change even if capacity is not updated.
Not sure whether it matters.
> + }
> +
> + 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);
> +
empty line :)
> +}
> +
> +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);
What does md_misc stand for? Would virtblk_wq be a better name?
> + 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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