Re: [Xen-devel] [PATCH] xen-blkback: convert hole punching to discard request on loop devices

[Li Dongyang <lidongyang@xxxxxxxxxx>]

On Wed, Nov 9, 2011 at 12:01 AM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>>>> On 07.11.11 at 09:34, Li Dongyang <lidongyang@xxxxxxxxxx> wrote:
>> As of dfaa2ef68e80c378e610e3c8c536f1c239e8d3ef, loop devices support
>> discard request now. We could just issue a discard request, and
>> the loop driver will punch the hole for us, so we don't need to touch
>> the internals of loop device and punch the hole ourselves, Thanks.
>
> Looking at what the loop driver now does - doesn't the original code
> here lack support for lo_offset being non-zero then? If so, should we
> fix this in pre-3.2 kernels?
yes, you are right, but will we ever setup the loop device with
lo_offset non-zero?
I don't think so but I'm not sure.
>
> Jan
>
>> Signed-off-by: Li Dongyang <lidongyang@xxxxxxxxxx>
>> ---
>>  drivers/block/xen-blkback/blkback.c |   21 +++------------------
>>  1 files changed, 3 insertions(+), 18 deletions(-)
>>
>> diff --git a/drivers/block/xen-blkback/blkback.c
>> b/drivers/block/xen-blkback/blkback.c
>> index 15ec4db..ad365a7 100644
>> --- a/drivers/block/xen-blkback/blkback.c
>> +++ b/drivers/block/xen-blkback/blkback.c
>> @@ -39,9 +39,6 @@
>>  #include <linux/list.h>
>>  #include <linux/delay.h>
>>  #include <linux/freezer.h>
>> -#include <linux/loop.h>
>> -#include <linux/falloc.h>
>> -#include <linux/fs.h>
>>
>>  #include <xen/events.h>
>>  #include <xen/page.h>
>> @@ -422,25 +419,13 @@ static void xen_blk_discard(struct xen_blkif *blkif,
>> struct blkif_request *req)
>>       int status = BLKIF_RSP_OKAY;
>>       struct block_device *bdev = blkif->vbd.bdev;
>>
>> -     if (blkif->blk_backend_type == BLKIF_BACKEND_PHY)
>> -             /* just forward the discard request */
>> +     if (blkif->blk_backend_type == BLKIF_BACKEND_PHY ||
>> +         blkif->blk_backend_type == BLKIF_BACKEND_FILE)
>>               err = blkdev_issue_discard(bdev,
>>                               req->u.discard.sector_number,
>>                               req->u.discard.nr_sectors,
>>                               GFP_KERNEL, 0);
>> -     else if (blkif->blk_backend_type == BLKIF_BACKEND_FILE) {
>> -             /* punch a hole in the backing file */
>> -             struct loop_device *lo = bdev->bd_disk->private_data;
>> -             struct file *file = lo->lo_backing_file;
>> -
>> -             if (file->f_op->fallocate)
>> -                     err = file->f_op->fallocate(file,
>> -                             FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE,
>> -                             req->u.discard.sector_number << 9,
>> -                             req->u.discard.nr_sectors << 9);
>> -             else
>> -                     err = -EOPNOTSUPP;
>> -     } else
>> +     else
>>               err = -EOPNOTSUPP;
>>
>>       if (err == -EOPNOTSUPP) {
>
>
>
>

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