linux-kernel - Re: [PATCH 3/3] nbd: map DISCARD requests to a new nbd request type

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Date:	Wed, 7 Sep 2011 21:13:47 -0400
From:	Paul Clements <paul.clements@...sios.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org
Subject: Re: [PATCH 3/3] nbd: map DISCARD requests to a new nbd request type

On Wed, Sep 7, 2011 at 10:41 AM, Paolo Bonzini <pbonzini@...hat.com> wrote:
> When the feature is enabled, set QUEUE_FLAG_DISCARD and transmit those as
> NBD_CMD_TRIM requests.
>
> I used "trim" instead of "discard" to avoid confusion with the existing
> NBD_CMD_DISC that is used for disconnect.

This patchset looks good to me.

--
Paul

> Cc: Paul Clements <Paul.Clements@...eleye.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  drivers/block/nbd.c |   15 ++++++++++++---
>  include/linux/nbd.h |    4 +++-
>  2 files changed, 15 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> index c4fe9c8..71ebaab 100644
> --- a/drivers/block/nbd.c
> +++ b/drivers/block/nbd.c
> @@ -98,6 +98,7 @@ static const char *nbdcmd_to_ascii(int cmd)
>        case  NBD_CMD_READ: return "read";
>        case NBD_CMD_WRITE: return "write";
>        case  NBD_CMD_DISC: return "disconnect";
> +       case  NBD_CMD_TRIM: return "trim (discard)";
>        }
>        return "invalid";
>  }
> @@ -454,9 +455,13 @@ static void nbd_handle_req(struct nbd_device *lo, struct request *req)
>        if (req->cmd_type != REQ_TYPE_FS)
>                goto error_out;
>
> -       if (rq_data_dir(req) == WRITE)
> -               nbd_cmd(req) = NBD_CMD_WRITE;
> -       else
> +       if (rq_data_dir(req) == WRITE) {
> +               if ((req->cmd_flags & REQ_DISCARD)) {
> +                       WARN_ON(!(lo->flags & NBD_FEATURE_TRIM));
> +                       nbd_cmd(req) = NBD_CMD_TRIM;
> +               } else
> +                       nbd_cmd(req) = NBD_CMD_WRITE;
> +       } else
>                nbd_cmd(req) = NBD_CMD_READ;
>
>        req->errors = 0;
> @@ -659,6 +664,9 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *lo,
>                        return -EINVAL;
>
>                mutex_unlock(&lo->tx_lock);
> +               if (lo->flags & NBD_FEATURE_TRIM)
> +                       queue_flag_set_unlocked(QUEUE_FLAG_DISCARD,
> +                                               lo->disk->queue);
>
>                thread = kthread_create(nbd_thread, lo, lo->disk->disk_name);
>                if (IS_ERR(thread)) {
> @@ -677,6 +685,7 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *lo,
>                lo->file = NULL;
>                nbd_clear_que(lo);
>                printk(KERN_WARNING "%s: queue cleared\n", lo->disk->disk_name);
> +               queue_flag_clear_unlocked(QUEUE_FLAG_DISCARD, lo->disk->queue);
>                if (file)
>                        fput(file);
>                lo->flags = 0;
> @@ -796,6 +805,9 @@ static int __init nbd_init(void)
>                 * Tell the block layer that we are not a rotational device
>                 */
>                queue_flag_set_unlocked(QUEUE_FLAG_NONROT, disk->queue);
> +               disk->queue->limits.discard_granularity = 512;
> +               disk->queue->limits.max_discard_sectors = UINT_MAX;
> +               disk->queue->limits.discard_zeroes_data = 0;
>        }
>
>        if (register_blkdev(NBD_MAJOR, "nbd")) {
> diff --git a/include/linux/nbd.h b/include/linux/nbd.h
> index 926f19d..7048463 100644
> --- a/include/linux/nbd.h
> +++ b/include/linux/nbd.h
> @@ -33,11 +33,13 @@
>  * not want any overlap.  Bits 32-63 are reserved because they
>  * are inaccessible on 32-bit platforms.  */
>  #define NBD_FEATURE_RESERVED   0xFFFFFFFF00000003LL
> +#define NBD_FEATURE_TRIM       (1 << 2)
>
>  enum {
>        NBD_CMD_READ = 0,
>        NBD_CMD_WRITE = 1,
> -       NBD_CMD_DISC = 2
> +       NBD_CMD_DISC = 2,
> +       NBD_CMD_TRIM = 3
>  };
>
>  #define nbd_cmd(req) ((req)->cmd[0])
> --
> 1.7.6
>
>
--
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