Re: [Qemu-devel] [PATCH V7 05/14] block: add snapshot info query function bdrv_query_snapshot_infolist()

[Markus Armbruster]

Wenchao Xia <address@hidden> writes:

>   This patch add function bdrv_query_snapshot_infolist(), which will

adds

> return snapshot info of an image in qmp object format. The implementation
> code are based on the code moved from qemu-img.c with modification to fit more

implementation is based

> for qmp based block layer API.
>   To help filter out snapshot info not needed, a call back function is
> added in bdrv_query_snapshot_infolist().
>   bdrv_can_read_snapshot() should be called before call this function,
> to avoid got *errp set unexpectedly.

"avoid getting"

Not sure about "should".  Couldn't a caller safely call this with a
non-snapshot bs argument, and simply deal with the error?

Long lines, and unusual paragraph formatting.  Here's how we usually do
this:

This patch adds function bdrv_query_snapshot_infolist(), which will
return snapshot info of an image in qmp object format. The
implementation is based on the code moved from qemu-img.c with
modification to fit more for qmp based block layer API.

To help filter out snapshot info not needed, a call back function is
added in bdrv_query_snapshot_infolist().

bdrv_can_read_snapshot() should be called before call this function, to
avoid getting *errp set unexpectedly.

> Signed-off-by: Wenchao Xia <address@hidden>
> Reviewed-by: Eric Blake <address@hidden>
> ---
>  block.c               |   60 ++++++++++++++++++++++++++++++++++++++----------
>  include/block/block.h |    8 +++++-
>  qemu-img.c            |    8 +++++-
>  3 files changed, 61 insertions(+), 15 deletions(-)
>
> diff --git a/block.c b/block.c
> index 368b37c..8d0145a 100644
> --- a/block.c
> +++ b/block.c
> @@ -2813,29 +2813,62 @@ int coroutine_fn 
> bdrv_co_is_allocated_above(BlockDriverState *top,
>      return 0;
>  }
>  
> -void collect_snapshots(BlockDriverState *bs , ImageInfo *info)
> +SnapshotInfoList *bdrv_query_snapshot_infolist(BlockDriverState *bs,
> +                                               SnapshotFilterFunc filter,
> +                                               void *opaque,
> +                                               Error **errp)
>  {
>      int i, sn_count;
>      QEMUSnapshotInfo *sn_tab = NULL;
> -    SnapshotInfoList *info_list, *cur_item = NULL;
> +    SnapshotInfoList *info_list, *cur_item = NULL, *head = NULL;
> +    SnapshotInfo *info;
> +
>      sn_count = bdrv_snapshot_list(bs, &sn_tab);
> +    if (sn_count < 0) {
> +        /* Now bdrv_snapshot_list() use negative value to tip error, so a 
> check
> +         * of it was done here. In future errp can be set by that function
> +         * itself, by changing the call back functions in c files in ./block.
> +         */

I doubt we need this comment.

> +        const char *dev = bdrv_get_device_name(bs);
> +        switch (sn_count) {
> +        case -ENOMEDIUM:
> +            error_setg(errp, "Device '%s' is not inserted.", dev);

We generally don't end error messages with a period.  Please remove it
from this and other messages.

> +            break;
> +        case -ENOTSUP:
> +            error_setg(errp,
> +                       "Device '%s' does not support internal snapshot.",

internal snapshots

> +                       dev);
> +            break;
> +        default:
> +            error_setg(errp,
> +                       "Device '%s' got '%d' for bdrv_snapshot_list(), "
> +                       "message '%s'.",
> +                       dev, sn_count, strerror(-sn_count));

               error_setg(errp, "Can't list snapshots of device '%s': %s",
                          dev, sterror(-sn_count));

> +            break;
> +        }
> +        return NULL;
> +    }
>  
>      for (i = 0; i < sn_count; i++) {
> -        info->has_snapshots = true;
> -        info_list = g_new0(SnapshotInfoList, 1);
> +        if (filter && filter(&sn_tab[i], opaque) != 0) {
> +            continue;
> +        }

Is the filter feature really worth it?  If yes, should it be added in a
separate patch?

>  
> -        info_list->value                = g_new0(SnapshotInfo, 1);
> -        info_list->value->id            = g_strdup(sn_tab[i].id_str);
> -        info_list->value->name          = g_strdup(sn_tab[i].name);
> -        info_list->value->vm_state_size = sn_tab[i].vm_state_size;
> -        info_list->value->date_sec      = sn_tab[i].date_sec;
> -        info_list->value->date_nsec     = sn_tab[i].date_nsec;
> -        info_list->value->vm_clock_sec  = sn_tab[i].vm_clock_nsec / 
> 1000000000;
> -        info_list->value->vm_clock_nsec = sn_tab[i].vm_clock_nsec % 
> 1000000000;
> +        info = g_new0(SnapshotInfo, 1);
> +        info->id            = g_strdup(sn_tab[i].id_str);
> +        info->name          = g_strdup(sn_tab[i].name);
> +        info->vm_state_size = sn_tab[i].vm_state_size;
> +        info->date_sec      = sn_tab[i].date_sec;
> +        info->date_nsec     = sn_tab[i].date_nsec;
> +        info->vm_clock_sec  = sn_tab[i].vm_clock_nsec / 1000000000;
> +        info->vm_clock_nsec = sn_tab[i].vm_clock_nsec % 1000000000;
> +
> +        info_list = g_new0(SnapshotInfoList, 1);
> +        info_list->value = info;
>  
>          /* XXX: waiting for the qapi to support qemu-queue.h types */
>          if (!cur_item) {
> -            info->snapshots = cur_item = info_list;
> +            head = cur_item = info_list;
>          } else {
>              cur_item->next = info_list;
>              cur_item = info_list;
> @@ -2844,6 +2877,7 @@ void collect_snapshots(BlockDriverState *bs , ImageInfo 
> *info)
>      }
>  
>      g_free(sn_tab);
> +    return head;
>  }
>  
>  void collect_image_info(BlockDriverState *bs,
> diff --git a/include/block/block.h b/include/block/block.h
> index e6d915c..51a14f2 100644
> --- a/include/block/block.h
> +++ b/include/block/block.h
> @@ -319,6 +319,13 @@ void bdrv_get_backing_filename(BlockDriverState *bs,
>                                 char *filename, int filename_size);
>  void bdrv_get_full_backing_filename(BlockDriverState *bs,
>                                      char *dest, size_t sz);
> +
> +typedef int (*SnapshotFilterFunc)(const QEMUSnapshotInfo *sn, void *opaque);
> +/* assume bs is already opened, use qapi_free_* to free returned value. */

Pretty much all functions assume bs is open, hardly worth a comment.

> +SnapshotInfoList *bdrv_query_snapshot_infolist(BlockDriverState *bs,
> +                                               SnapshotFilterFunc filter,
> +                                               void *opaque,
> +                                               Error **errp);
>  BlockInfo *bdrv_query_info(BlockDriverState *s);
>  BlockStats *bdrv_query_stats(const BlockDriverState *bs);
>  bool bdrv_can_read_snapshot(BlockDriverState *bs);
> @@ -450,7 +457,6 @@ int bdrv_debug_breakpoint(BlockDriverState *bs, const 
> char *event,
>  int bdrv_debug_resume(BlockDriverState *bs, const char *tag);
>  bool bdrv_debug_is_suspended(BlockDriverState *bs, const char *tag);
>  
> -void collect_snapshots(BlockDriverState *bs , ImageInfo *info);
>  void collect_image_info(BlockDriverState *bs,
>                          ImageInfo *info,
>                          const char *filename);
> diff --git a/qemu-img.c b/qemu-img.c
> index b650d17..1034cc5 100644
> --- a/qemu-img.c
> +++ b/qemu-img.c
> @@ -1280,7 +1280,13 @@ static ImageInfoList *collect_image_info_list(const 
> char *filename,
>  
>          info = g_new0(ImageInfo, 1);
>          collect_image_info(bs, info, filename);
> -        collect_snapshots(bs, info);
> +        if (bdrv_can_read_snapshot(bs)) {
> +            info->snapshots = bdrv_query_snapshot_infolist(bs, NULL,
> +                                                           NULL, NULL);
> +            if (info->snapshots) {
> +                info->has_snapshots = true;
> +            }
> +        }
>  
>          elem = g_new0(ImageInfoList, 1);
>          elem->value = info;

Silently ignores errors, but the old code does so, too.

QAPI's has_FOO is pointless when FOO is a pointer.  Not your fault.