[2/6] block: Add optional device argument to query-block

This allows querying one specific BlockDriverState instead of a list of
all drives.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block/qapi.c         | 15 +++++++++++++--
 hmp.c                |  6 +++---
 qapi/block-core.json |  8 ++++++--
 3 files changed, 22 insertions(+), 7 deletions(-)

Kevin Wolf <kwolf@redhat.com> writes:

> This allows querying one specific BlockDriverState instead of a list of
> all drives.

I've long resisted optional arguments to limit list-valued queries,
because I believe the additional interface complexity isn't worth the
additional utility.  But resistance might be futile.

We have one only query- with an optional limiting arguement[*]:
query-rx-filter.

If we go down this route, then I'd prefer to have such optional limiting
for all query- commands returning lists of elements describing some
aspect of a named object.  Preference != demand.

>
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  block/qapi.c         | 15 +++++++++++++--
>  hmp.c                |  6 +++---
>  qapi/block-core.json |  8 ++++++--
>  3 files changed, 22 insertions(+), 7 deletions(-)
>
> diff --git a/block/qapi.c b/block/qapi.c
> index 6b43bc3..2a060d3 100644
> --- a/block/qapi.c
> +++ b/block/qapi.c
> @@ -367,13 +367,24 @@ static BlockStats *bdrv_query_stats(const BlockDriverState *bs)
>      return s;
>  }
>  
> -BlockInfoList *qmp_query_block(Error **errp)
> +BlockInfoList *qmp_query_block(bool has_device, const char *device,
> +                               Error **errp)
>  {
>      BlockInfoList *head = NULL, **p_next = &head;
>      BlockDriverState *bs = NULL;
>      Error *local_err = NULL;
>  
> -     while ((bs = bdrv_next(bs))) {
> +    if (has_device) {
> +        bs = bdrv_find(device);
> +        if (bs == NULL) {
> +            error_setg(errp, "Device not found");
> +            goto err;
> +        }
> +    } else {
> +        bs = bdrv_next(NULL);
> +    }
> +
> +    for (; bs; (bs = has_device ? NULL : bdrv_next(bs))) {
>          BlockInfoList *info = g_malloc0(sizeof(*info));
>          bdrv_query_info(bs, &info->value, &local_err);
>          if (local_err) {

I'd find

    for (bs = bdrv_next(NULL); bs; bs == bdrv_next(bs)) {
        if (device && strcmp(device, bs->device)) {
            continue;
        }
    }

simpler and clearer.  It's how qmp_query_rx_filter() works.

> diff --git a/hmp.c b/hmp.c
> index c3846b8..02eee80 100644
> --- a/hmp.c
> +++ b/hmp.c
> @@ -298,7 +298,7 @@ void hmp_info_block(Monitor *mon, const QDict *qdict)
>      const char *device = qdict_get_try_str(qdict, "device");
>      bool verbose = qdict_get_try_bool(qdict, "verbose", 0);
>  
> -    block_list = qmp_query_block(NULL);
> +    block_list = qmp_query_block(false, NULL, NULL);
>  
>      for (info = block_list; info; info = info->next) {
>          if (device && strcmp(device, info->value->device)) {
> @@ -847,7 +847,7 @@ void hmp_cont(Monitor *mon, const QDict *qdict)
>      BlockInfoList *bdev_list, *bdev;
>      Error *err = NULL;
>  
> -    bdev_list = qmp_query_block(NULL);
> +    bdev_list = qmp_query_block(false, NULL, NULL);
>      for (bdev = bdev_list; bdev; bdev = bdev->next) {
>          if (key_is_missing(bdev->value)) {
>              monitor_read_block_device_key(mon, bdev->value->device,
> @@ -1588,7 +1588,7 @@ void hmp_nbd_server_start(Monitor *mon, const QDict *qdict)
>      /* Then try adding all block devices.  If one fails, close all and
>       * exit.
>       */
> -    block_list = qmp_query_block(NULL);
> +    block_list = qmp_query_block(false, NULL, NULL);
>  
>      for (info = block_list; info; info = info->next) {
>          if (!info->value->has_inserted) {
> diff --git a/qapi/block-core.json b/qapi/block-core.json
> index c53b587..ddc3fe0 100644
> --- a/qapi/block-core.json
> +++ b/qapi/block-core.json
> @@ -354,13 +354,17 @@
>  ##
>  # @query-block:
>  #
> -# Get a list of BlockInfo for all virtual block devices.
> +# Get a list of BlockInfo for all or one specific virtual block device.
> +#
> +# @device: #optional The id of the block device to inspect. (Since 2.2)
>  #
>  # Returns: a list of @BlockInfo describing each virtual block device
>  #
>  # Since: 0.14.0
>  ##

This is how we document query-rx-filter:

##
# @query-rx-filter:
#
# Return rx-filter information for all NICs (or for the given NIC).
#
# @name: #optional net client name
#
# Returns: list of @RxFilterInfo for all NICs (or for the given NIC).
#          Returns an error if the given @name doesn't exist, or given
#          NIC doesn't support rx-filter querying, or given net client
#          isn't a NIC.
#
# Since: 1.6
##

I find that slightly clearer.  Perhaps you'd like to steal from it.

> -{ 'command': 'query-block', 'returns': ['BlockInfo'] }
> +{ 'command': 'query-block',
> +  'data': { '*device': 'str' },
> +  'returns': ['BlockInfo'] }
>  
>  ##
>  # @BlockDeviceStats:


[*] Yes, I objected to the argument, but I didn't insist.  I won't
insist now.