[06/12] nbd: support NBD_CMD_TRIM in the server

Map it to bdrv_discard.  The server can now expose NBD_FLAG_SEND_TRIM.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 block/nbd.c |   31 +++++++++++++++++++++++++++++++
 nbd.c       |    9 ++++++++-
 2 files changed, 39 insertions(+), 1 deletions(-)

Am 08.09.2011 17:24, schrieb Paolo Bonzini:
> Map it to bdrv_discard.  The server can now expose NBD_FLAG_SEND_TRIM.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  block/nbd.c |   31 +++++++++++++++++++++++++++++++
>  nbd.c       |    9 ++++++++-
>  2 files changed, 39 insertions(+), 1 deletions(-)
> 
> diff --git a/block/nbd.c b/block/nbd.c
> index 5a7812c..964caa8 100644
> --- a/block/nbd.c
> +++ b/block/nbd.c
> @@ -275,6 +275,36 @@ static int nbd_flush(BlockDriverState *bs)
>      return 0;
>  }
>  
> +static int nbd_discard(BlockDriverState *bs, int64_t sector_num,
> +                       int nb_sectors)
> +{
> +    BDRVNBDState *s = bs->opaque;
> +    struct nbd_request request;
> +    struct nbd_reply reply;
> +
> +    if (!(s->nbdflags & NBD_FLAG_SEND_TRIM)) {
> +        return 0;
> +    }
> +    request.type = NBD_CMD_TRIM;
> +    request.handle = (uint64_t)(intptr_t)bs;
> +    request.from = sector_num * 512;;
> +    request.len = nb_sectors * 512;
> +
> +    if (nbd_send_request(s->sock, &request) == -1)
> +        return -errno;
> +
> +    if (nbd_receive_reply(s->sock, &reply) == -1)
> +        return -errno;
> +
> +    if (reply.error !=0)
> +        return -reply.error;
> +
> +    if (reply.handle != request.handle)
> +        return -EIO;
> +
> +    return 0;
> +}
> +
>  static void nbd_close(BlockDriverState *bs)
>  {
>      BDRVNBDState *s = bs->opaque;
> @@ -299,6 +329,7 @@ static BlockDriver bdrv_nbd = {
>      .bdrv_write		= nbd_write,
>      .bdrv_close		= nbd_close,
>      .bdrv_flush		= nbd_flush,
> +    .bdrv_discard	= nbd_discard,
>      .bdrv_getlength	= nbd_getlength,
>      .protocol_name	= "nbd",
>  };
> diff --git a/nbd.c b/nbd.c
> index b65fb4a..f089904 100644
> --- a/nbd.c
> +++ b/nbd.c
> @@ -194,7 +194,7 @@ int nbd_negotiate(int csock, off_t size, uint32_t flags)
>      cpu_to_be64w((uint64_t*)(buf + 8), 0x00420281861253LL);
>      cpu_to_be64w((uint64_t*)(buf + 16), size);
>      cpu_to_be32w((uint32_t*)(buf + 24),
> -                 flags | NBD_FLAG_HAS_FLAGS |
> +                 flags | NBD_FLAG_HAS_FLAGS | NBD_FLAG_SEND_TRIM |
>                   NBD_FLAG_SEND_FLUSH | NBD_FLAG_SEND_FUA);
>      memset(buf + 28, 0, 124);
>  
> @@ -703,6 +703,13 @@ int nbd_trip(BlockDriverState *bs, int csock, off_t size, uint64_t dev_offset,
>          if (nbd_send_reply(csock, &reply) == -1)
>              return -1;
>          break;
> +    case NBD_CMD_TRIM:
> +        TRACE("Request type is TRIM");
> +        bdrv_discard(bs, (request.from + dev_offset) / 512,
> +                     request.len / 512);

Errors are completely ignored? Does the NBD protocol not allow to return
an error?

Kevin

On 09/13/2011 03:58 PM, Kevin Wolf wrote:
>> >  +    case NBD_CMD_TRIM:
>> >  +        TRACE("Request type is TRIM");
>> >  +        bdrv_discard(bs, (request.from + dev_offset) / 512,
>> >  +                     request.len / 512);
>
> Errors are completely ignored? Does the NBD protocol not allow to return
> an error?

Actually it does, will fix.

Paolo

On Thu, Sep 08, 2011 at 05:24:59PM +0200, Paolo Bonzini wrote:
> Map it to bdrv_discard.  The server can now expose NBD_FLAG_SEND_TRIM.

Note that discard support without a way to communicate the alignment/size
requirements, and without the discard_zeroes_data flag is pretty much
useless.  Can you work with the upstream developers to make sure it's
actually useful?

On 09/14/2011 05:44 PM, Christoph Hellwig wrote:
>> Map it to bdrv_discard.  The server can now expose NBD_FLAG_SEND_TRIM.
>
> Note that discard support without a way to communicate the alignment/size
> requirements,

Yep, especially because alignment can be as small as 512 for sparse raw, 
and as high as 65536 for qcow2...

> and without the discard_zeroes_data flag is pretty much
> useless.

... but right now in QEMU it is most useful with qcow2, so 
!discard_zeroes_data is pretty much the best you can do.

In general, QEMU's block layer does not really do much to pass 
information on discard features, which is why I didn't think much about 
these bits.  I'm interested in making NBD as featureful as the QEMU 
block layer, but beyond that not much. :)

Still you're obviously right, I'll talk to upstream.

Paolo