Re: [Qemu-devel] [PATCH v4 1/3] qmp: Add command 'blockdev-backup'

[Max Reitz <mreitz@redhat.com>]

On 2014-12-04 at 03:29, Fam Zheng wrote:
> Similar to drive-backup, but this command uses a device id as target
> instead of creating/opening an image file.
>
> Also add blocker on target bs, since the target is also a named device
> now.
>
> Add check and report error for bs == target which became possible but is
> an illegal case with introduction of blockdev-backup.
>
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>   block/backup.c       | 28 +++++++++++++++++++++++++++
>   blockdev.c           | 48 ++++++++++++++++++++++++++++++++++++++++++++++
>   qapi/block-core.json | 54 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>   qmp-commands.hx      | 44 ++++++++++++++++++++++++++++++++++++++++++
>   4 files changed, 174 insertions(+)
>
> diff --git a/block/backup.c b/block/backup.c
> index 792e655..b944dd4 100644
> --- a/block/backup.c
> +++ b/block/backup.c
> @@ -360,6 +360,7 @@ static void coroutine_fn backup_run(void *opaque)
>       hbitmap_free(job->bitmap);
>   
>       bdrv_iostatus_disable(target);
> +    bdrv_op_unblock_all(target, job->common.blocker);
>   
>       data = g_malloc(sizeof(*data));
>       data->ret = ret;
> @@ -379,6 +380,11 @@ void backup_start(BlockDriverState *bs, BlockDriverState *target,
>       assert(target);
>       assert(cb);
>   
> +    if (bs == target) {
> +        error_setg(errp, "Source and target cannot be the same");
> +        return;
> +    }
> +
>       if ((on_source_error == BLOCKDEV_ON_ERROR_STOP ||
>            on_source_error == BLOCKDEV_ON_ERROR_ENOSPC) &&
>           !bdrv_iostatus_is_enabled(bs)) {
> @@ -386,6 +392,26 @@ void backup_start(BlockDriverState *bs, BlockDriverState *target,
>           return;
>       }
>   
> +    if (!bdrv_is_inserted(bs)) {
> +        error_setg(errp, "Devie is not inserted: %s",

*Device

> +                   bdrv_get_device_name(bs));
> +        return;
> +    }
> +
> +    if (!bdrv_is_inserted(target)) {
> +        error_setg(errp, "Devie is not inserted: %s",

Here, too.

> +                   bdrv_get_device_name(target));
> +        return;
> +    }
> +
> +    if (bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_BACKUP_SOURCE, errp)) {
> +        return;
> +    }
> +
> +    if (bdrv_op_is_blocked(target, BLOCK_OP_TYPE_BACKUP_TARGET, errp)) {
> +        return;
> +    }
> +
>       len = bdrv_getlength(bs);
>       if (len < 0) {
>           error_setg_errno(errp, -len, "unable to get length for '%s'",
> @@ -399,6 +425,8 @@ void backup_start(BlockDriverState *bs, BlockDriverState *target,
>           return;
>       }
>   
> +    bdrv_op_block_all(target, job->common.blocker);
> +
>       job->on_source_error = on_source_error;
>       job->on_target_error = on_target_error;
>       job->target = target;
> diff --git a/blockdev.c b/blockdev.c
> index 5651a8e..f44441a 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -2240,6 +2240,8 @@ void qmp_drive_backup(const char *device, const char *target,
>       aio_context = bdrv_get_aio_context(bs);
>       aio_context_acquire(aio_context);
>   
> +    /* Although backup_run has this check too, we need to use bs->drv below, so
> +     * do an early check redundantly. */
>       if (!bdrv_is_inserted(bs)) {
>           error_set(errp, QERR_DEVICE_HAS_NO_MEDIUM, device);
>           goto out;
> @@ -2256,6 +2258,7 @@ void qmp_drive_backup(const char *device, const char *target,
>           }
>       }
>   
> +    /* Early check to avoid creating target */
>       if (bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_BACKUP_SOURCE, errp)) {
>           goto out;
>       }
> @@ -2323,6 +2326,51 @@ BlockDeviceInfoList *qmp_query_named_block_nodes(Error **errp)
>       return bdrv_named_nodes_list();
>   }
>   
> +void qmp_blockdev_backup(const char *device, const char *target,
> +                         enum MirrorSyncMode sync,
> +                         bool has_speed, int64_t speed,
> +                         bool has_on_source_error,
> +                         BlockdevOnError on_source_error,
> +                         bool has_on_target_error,
> +                         BlockdevOnError on_target_error,
> +                         Error **errp)
> +{
> +    BlockDriverState *bs;
> +    BlockDriverState *target_bs;
> +    Error *local_err = NULL;
> +
> +    if (!has_speed) {
> +        speed = 0;
> +    }
> +    if (!has_on_source_error) {
> +        on_source_error = BLOCKDEV_ON_ERROR_REPORT;
> +    }
> +    if (!has_on_target_error) {
> +        on_target_error = BLOCKDEV_ON_ERROR_REPORT;
> +    }
> +
> +    bs = bdrv_find(device);

Hmmmm, I once tried to rewrite some block jobs to use BlockBackend 
instead of BDS directly... Didn't work out so well. So, well, 
bdrv_find() is fine (although there is still the TODO above its 
definition which asks callers to use blk_by_name()...).

> +    if (!bs) {
> +        error_set(errp, QERR_DEVICE_NOT_FOUND, device);
> +        return;
> +    }
> +
> +    target_bs = bdrv_find(target);
> +    if (!target_bs) {
> +        error_set(errp, QERR_DEVICE_NOT_FOUND, target);
> +        return;
> +    }
> +
> +    bdrv_ref(target_bs);
> +    bdrv_set_aio_context(target_bs, bdrv_get_aio_context(bs));

In the cover letter you said you were acquiring the AIO context but 
you're not. Something like the aio_context_acquire() call in 
qmp_drive_backup() seems missing.

> +    backup_start(bs, target_bs, speed, sync, on_source_error, on_target_error,
> +                 block_job_cb, bs, &local_err);
> +    if (local_err != NULL) {
> +        bdrv_unref(target_bs);

Hm, as far as I can see, backup_complete() is always run, regardless of 
the operation status. backup_complete() in turn calls 
bdrv_unref(s->target), so this seems unnecessary to me.

> +        error_propagate(errp, local_err);
> +    }
> +}
> +
>   #define DEFAULT_MIRROR_BUF_SIZE   (10 << 20)
>   
>   void qmp_drive_mirror(const char *device, const char *target,
> diff --git a/qapi/block-core.json b/qapi/block-core.json
> index 6e8db15..d9f0598 100644
> --- a/qapi/block-core.json
> +++ b/qapi/block-core.json
> @@ -703,6 +703,41 @@
>               '*on-target-error': 'BlockdevOnError' } }
>   
>   ##
> +# @BlockdevBackup
> +#
> +# @device: the name of the device which should be copied.
> +#
> +# @target: the name of the backup target device.
> +#
> +# @sync: what parts of the disk image should be copied to the destination
> +#        (all the disk, only the sectors allocated in the topmost image, or
> +#        only new I/O).
> +#
> +# @speed: #optional the maximum speed, in bytes per second. The default is 0,
> +#         for unlimited.
> +#
> +# @on-source-error: #optional the action to take on an error on the source,
> +#                   default 'report'.  'stop' and 'enospc' can only be used
> +#                   if the block device supports io-status (see BlockInfo).
> +#
> +# @on-target-error: #optional the action to take on an error on the target,
> +#                   default 'report' (no limitations, since this applies to
> +#                   a different block device than @device).
> +#
> +# Note that @on-source-error and @on-target-error only affect background I/O.
> +# If an error occurs during a guest write request, the device's rerror/werror
> +# actions will be used.
> +#
> +# Since: 2.3
> +##
> +{ 'type': 'BlockdevBackup',
> +  'data': { 'device': 'str', 'target': 'str',
> +            'sync': 'MirrorSyncMode',
> +            '*speed': 'int',
> +            '*on-source-error': 'BlockdevOnError',
> +            '*on-target-error': 'BlockdevOnError' } }
> +
> +##
>   # @blockdev-snapshot-sync
>   #
>   # Generates a synchronous snapshot of a block device.
> @@ -822,6 +857,25 @@
>   { 'command': 'drive-backup', 'data': 'DriveBackup' }
>   
>   ##
> +# @blockdev-backup
> +#
> +# Start a point-in-time copy of a block device to a new destination.  The
> +# status of ongoing blockdev-backup operations can be checked with
> +# query-block-jobs where the BlockJobInfo.type field has the value 'backup'.
> +# The operation can be stopped before it has completed using the
> +# block-job-cancel command.
> +#
> +# For the arguments, see the documentation of BlockdevBackup.
> +#
> +# Returns: Nothing on success.
> +#          If @device or @target is not a valid block device, DeviceNotFound.
> +#
> +# Since 2.3
> +##
> +{ 'command': 'blockdev-backup', 'data': 'BlockdevBackup' }
> +
> +
> +##
>   # @query-named-block-nodes
>   #
>   # Get the named block driver list
> diff --git a/qmp-commands.hx b/qmp-commands.hx
> index d4b0010..3b209b2 100644
> --- a/qmp-commands.hx
> +++ b/qmp-commands.hx
> @@ -1094,6 +1094,50 @@ Example:
>                                                  "sync": "full",
>                                                  "target": "backup.img" } }
>   <- { "return": {} }
> +
> +EQMP
> +
> +    {
> +        .name       = "blockdev-backup",
> +        .args_type  = "sync:s,device:B,target:B,speed:i?,"
> +                      "on-source-error:s?,on-target-error:s?",
> +        .mhandler.cmd_new = qmp_marshal_input_blockdev_backup,
> +    },
> +
> +SQMP
> +blockdev-backup
> +------------
> +
> +The device version of drive-backup: this command takes an existing named device
> +as backup target.
> +
> +Arguments:
> +
> +- "device": the name of the device which should be copied.
> +            (json-string)
> +- "target": the target of the new image. If the file exists, or if it is a
> +            device, the existing file/device will be used as the new
> +            destination.  If it does not exist, a new file will be created.
> +            (json-string)
> +- "sync": what parts of the disk image should be copied to the destination;
> +          possibilities include "full" for all the disk, "top" for only the
> +          sectors allocated in the topmost image, or "none" to only replicate
> +          new I/O (MirrorSyncMode).
> +- "speed": the maximum speed, in bytes per second (json-int, optional)
> +- "on-source-error": the action to take on an error on the source, default
> +                     'report'.  'stop' and 'enospc' can only be used
> +                     if the block device supports io-status.
> +                     (BlockdevOnError, optional)
> +- "on-target-error": the action to take on an error on the target, default
> +                     'report' (no limitations, since this applies to
> +                     a different block device than device).
> +                     (BlockdevOnError, optional)
> +
> +Example:
> +-> { "execute": "blockdev-backup", "arguments": { "device": "src-id",
> +                                                  "target": "tgt-id" } }

Isn't "sync" missing?

Max

> +<- { "return": {} }
> +
>   EQMP
>   
>       {