Re: [Xen-devel] [PATCH v3] xen-blk(front|back): Handle large physical sector disks

[Stefan Bader <stefan.bader@xxxxxxxxxxxxx>]

On 15.05.2013 17:02, Stefan Bader wrote:
> Changed the xenbus_gather but kept the xenbus_dev_error (without being fatal) 
> as
> that seems closer to the style of the other calls.

Was this ok as is or pending some answers/discussion which I may have not
given/missed?

-Stefan

> 
> -Stefan
> 
> From cddea87d842cc5feb427f3eedefc0566d69fb9b6 Mon Sep 17 00:00:00 2001
> From: Stefan Bader <stefan.bader@xxxxxxxxxxxxx>
> Date: Mon, 13 May 2013 16:28:15 +0200
> Subject: [PATCH] xen/blk: Use physical sector size for setup
> 
> Currently xen-blkback passes the logical sector size over xenbus and
> xen-blkfront sets up the paravirt disk with that logical block size.
> But newer drives usually have the logical sector size set to 512 for
> compatibility reasons and would show the actual sector size only in
> physical sector size.
> This results in the device being partitioned and accessed in dom0 with
> the correct sector size, but the guest thinks 512 bytes is the correct
> block size. And that results in poor performance.
> 
> To fix this, blkback gets modified to pass also physical-sector-size
> over xenbus and blkfront to use both values to set up the paravirt
> disk. I did not just change the passed in sector-size because I am
> not sure having a bigger logical sector size than the physical one
> is valid (and that would happen if a newer dom0 kernel hits an older
> domU kernel). Also this way a domU set up before should still be
> accessible (just some tools might detect the unaligned setup).
> 
> [v2: Make xenbus write failure non-fatal]
> [v3: Use xenbus_scanf instead of xenbus_gather]
> 
> Signed-off-by: Stefan Bader <stefan.bader@xxxxxxxxxxxxx>
> ---
>  drivers/block/xen-blkback/xenbus.c |    5 +++++
>  drivers/block/xen-blkfront.c       |   23 +++++++++++++++++++----
>  2 files changed, 24 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/block/xen-blkback/xenbus.c 
> b/drivers/block/xen-blkback/xenbus.c
> index 8bfd1bc..25463e3 100644
> --- a/drivers/block/xen-blkback/xenbus.c
> +++ b/drivers/block/xen-blkback/xenbus.c
> @@ -704,6 +704,11 @@ again:
>                                dev->nodename);
>               goto abort;
>       }
> +     err = xenbus_printf(xbt, dev->nodename, "physical-sector-size", "%u",
> +                         bdev_physical_block_size(be->blkif->vbd.bdev));
> +     if (err)
> +             xenbus_dev_error(dev, err, "writing %s/physical-sector-size",
> +                              dev->nodename);
> 
>       err = xenbus_transaction_end(xbt, 0);
>       if (err == -EAGAIN)
> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> index d89ef86..33b5618 100644
> --- a/drivers/block/xen-blkfront.c
> +++ b/drivers/block/xen-blkfront.c
> @@ -542,7 +542,8 @@ wait:
>               flush_requests(info);
>  }
> 
> -static int xlvbd_init_blk_queue(struct gendisk *gd, u16 sector_size)
> +static int xlvbd_init_blk_queue(struct gendisk *gd, u16 sector_size,
> +                             unsigned int physical_sector_size)
>  {
>       struct request_queue *rq;
>       struct blkfront_info *info = gd->private_data;
> @@ -564,6 +565,7 @@ static int xlvbd_init_blk_queue(struct gendisk *gd, u16
> sector_size)
> 
>       /* Hard sector size and max sectors impersonate the equiv. hardware. */
>       blk_queue_logical_block_size(rq, sector_size);
> +     blk_queue_physical_block_size(rq, physical_sector_size);
>       blk_queue_max_hw_sectors(rq, 512);
> 
>       /* Each segment in a request is up to an aligned page in size. */
> @@ -667,7 +669,8 @@ static char *encode_disk_name(char *ptr, unsigned int n)
> 
>  static int xlvbd_alloc_gendisk(blkif_sector_t capacity,
>                              struct blkfront_info *info,
> -                            u16 vdisk_info, u16 sector_size)
> +                            u16 vdisk_info, u16 sector_size,
> +                            unsigned int physical_sector_size)
>  {
>       struct gendisk *gd;
>       int nr_minors = 1;
> @@ -734,7 +737,7 @@ static int xlvbd_alloc_gendisk(blkif_sector_t capacity,
>       gd->driverfs_dev = &(info->xbdev->dev);
>       set_capacity(gd, capacity);
> 
> -     if (xlvbd_init_blk_queue(gd, sector_size)) {
> +     if (xlvbd_init_blk_queue(gd, sector_size, physical_sector_size)) {
>               del_gendisk(gd);
>               goto release;
>       }
> @@ -1395,6 +1398,7 @@ static void blkfront_connect(struct blkfront_info *info)
>  {
>       unsigned long long sectors;
>       unsigned long sector_size;
> +     unsigned int physical_sector_size;
>       unsigned int binfo;
>       int err;
>       int barrier, flush, discard, persistent;
> @@ -1437,6 +1441,16 @@ static void blkfront_connect(struct blkfront_info 
> *info)
>               return;
>       }
> 
> +     /*
> +      * physcial-sector-size is a newer field, so old backends may not
> +      * provide this. Assume physical sector size to be the same as
> +      * sector_size in that case.
> +      */
> +     err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
> +                        "physical-sector-size", "%u", &physical_sector_size);
> +     if (err != 1)
> +             physical_sector_size = sector_size;
> +
>       info->feature_flush = 0;
>       info->flush_op = 0;
> 
> @@ -1483,7 +1497,8 @@ static void blkfront_connect(struct blkfront_info *info)
>       else
>               info->feature_persistent = persistent;
> 
> -     err = xlvbd_alloc_gendisk(sectors, info, binfo, sector_size);
> +     err = xlvbd_alloc_gendisk(sectors, info, binfo, sector_size,
> +                               physical_sector_size);
>       if (err) {
>               xenbus_dev_fatal(info->xbdev, err, "xlvbd_add at %s",
>                                info->xbdev->otherend);
> 
> 
> 
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> http://lists.xen.org/xen-devel
>

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