Re: [Qemu-devel] [PATCH v2] block/rbd: add preallocation support

[Max Reitz <mreitz@redhat.com>]

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On 06.05.19 14:23, Stefano Garzarella wrote:
> This patch adds the support of preallocation (off/full) for the RBD
> block driver.
> If available, we use rbd_writesame() to quickly fill the image when
> full preallocation is required.
> 
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
> ---
> v2:
> - Use 4 KiB buffer for rbd_writesame() [Jason]
> - Use "rbd_concurrent_management_ops" and "stripe_unit" to limit
>   concurrent ops to the backing cluster [Jason]
> ---
>  block/rbd.c          | 188 +++++++++++++++++++++++++++++++++++++++----
>  qapi/block-core.json |   4 +-
>  2 files changed, 175 insertions(+), 17 deletions(-)

This patch conflicts a bit with the rbd file growth patch, so that would
need to be resolved in a v3.

But still, that doesn’t prevent me from reviewing it as it is:

> diff --git a/block/rbd.c b/block/rbd.c
> index 0c549c9935..bc54395e1c 100644
> --- a/block/rbd.c
> +++ b/block/rbd.c

[...]

> @@ -331,6 +333,147 @@ static void qemu_rbd_memset(RADOSCB *rcb, int64_t offs)

[...]

> +static int qemu_rbd_do_truncate(rados_t cluster, rbd_image_t image,
> +                                int64_t offset, PreallocMode prealloc,
> +                                Error **errp)
> +{

[...]

> +#ifdef LIBRBD_SUPPORTS_WRITESAME
> +        uint64_t stripe_unit, writesame_max_size;
> +        int max_concurrent_ops;
> +
> +        max_concurrent_ops = qemu_rbd_get_max_concurrent_ops(cluster);
> +        ret = rbd_get_stripe_unit(image, &stripe_unit);
> +        if (ret < 0) {
> +            error_setg_errno(errp, -ret, "Failed to get stripe unit");
> +            goto out;
> +        }
> +
> +        /*
> +         * We limit the rbd_writesame() size to avoid to spawn more then

s/then/than/

> +         * 'rbd_concurrent_management_ops' concurrent operations.
> +         */
> +        writesame_max_size = MIN(stripe_unit * max_concurrent_ops, INT_MAX);
> +#endif /* LIBRBD_SUPPORTS_WRITESAME */
> +
> +        buf = g_malloc(buf_size);
> +        /*
> +         * Some versions of rbd_writesame() discards writes of buffers with
> +         * all zeroes. In order to avoid this behaviour, we set the first byte
> +         * to one.
> +         */
> +        buf[0] = 1;

But I guess you’ll need to rewrite it as zero later, or the
“bdrv_rbd.bdrv_has_zero_init = bdrv_has_zero_init_1” is no longer quite
true.

[...]

> @@ -449,6 +603,16 @@ static int coroutine_fn qemu_rbd_co_create_opts(const char *filename,
>                                                     BLOCK_OPT_CLUSTER_SIZE, 0);
>      rbd_opts->has_cluster_size = (rbd_opts->cluster_size != 0);
>  
> +    prealloc = qemu_opt_get_del(opts, BLOCK_OPT_PREALLOC);
> +    rbd_opts->preallocation = qapi_enum_parse(&PreallocMode_lookup, prealloc,
> +                                              PREALLOC_MODE_OFF, &local_err);

You also need to set rbd_opts->has_preallocation to true.

> +    g_free(prealloc);
> +    if (local_err) {
> +        ret = -EINVAL;
> +        error_propagate(errp, local_err);
> +        goto exit;
> +    }
> +
>      options = qdict_new();
>      qemu_rbd_parse_filename(filename, options, &local_err);
>      if (local_err) {

[...]

> diff --git a/qapi/block-core.json b/qapi/block-core.json
> index 7ccbfff9d0..db25a4065b 100644
> --- a/qapi/block-core.json
> +++ b/qapi/block-core.json
> @@ -4277,13 +4277,15 @@
>  #                   point to a snapshot.
>  # @size             Size of the virtual disk in bytes
>  # @cluster-size     RBD object size
> +# @preallocation    Preallocation mode (allowed values: off, full)

There should be a "(Since: 4.1)" note here.

Max

>  #
>  # Since: 2.12
>  ##
>  { 'struct': 'BlockdevCreateOptionsRbd',
>    'data': { 'location':         'BlockdevOptionsRbd',
>              'size':             'size',
> -            '*cluster-size' :   'size' } }
> +            '*cluster-size' :   'size',
> +            '*preallocation':   'PreallocMode' } }
>  
>  ##
>  # @BlockdevVmdkSubformat:
> 



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