Re: [Qemu-devel] [PATCH v4 29/38] blockdev: Add blockdev-insert-medium

[Max Reitz <mreitz@redhat.com>]

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On 08.09.2015 11:13, Wen Congyang wrote:
> On 07/21/2015 01:45 AM, Max Reitz wrote:
>> And a helper function for that, which directly takes a pointer to the
>> BDS to be inserted instead of its node-name (which will be used for
>> implementing 'change' using blockdev-insert-medium).
>>
>> Signed-off-by: Max Reitz <mreitz@redhat.com>
>> ---
>>  blockdev.c           | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
>>  qapi/block-core.json | 17 +++++++++++++++++
>>  qmp-commands.hx      | 37 +++++++++++++++++++++++++++++++++++++
>>  3 files changed, 102 insertions(+)
>>
>> diff --git a/blockdev.c b/blockdev.c
>> index 481760a..a80d0e2 100644
>> --- a/blockdev.c
>> +++ b/blockdev.c
>> @@ -2164,6 +2164,54 @@ void qmp_blockdev_remove_medium(const char *device, Error **errp)
>>      }
>>  }
>>  
>> +static void qmp_blockdev_insert_anon_medium(const char *device,
>> +                                            BlockDriverState *bs, Error **errp)
>> +{
>> +    BlockBackend *blk;
>> +    bool has_device;
>> +
>> +    blk = blk_by_name(device);
>> +    if (!blk) {
>> +        error_set(errp, ERROR_CLASS_DEVICE_NOT_FOUND,
>> +                  "Device '%s' not found", device);
>> +        return;
>> +    }
>> +
>> +    /* For BBs without a device, we can exchange the BDS tree at will */
>> +    has_device = blk_get_attached_dev(blk);
>> +
>> +    if (has_device && !blk_dev_has_removable_media(blk)) {
>> +        error_setg(errp, "Device '%s' is not removable", device);
>> +        return;
>> +    }
>> +
>> +    if (has_device && !blk_dev_is_tray_open(blk)) {
>> +        error_setg(errp, "Tray of device '%s' is not open", device);
>> +        return;
>> +    }
>> +
>> +    if (blk_bs(blk)) {
>> +        error_setg(errp, "There already is a medium in device '%s'", device);
>> +        return;
>> +    }
>> +
>> +    blk_insert_bs(blk, bs);
>> +}
>> +
>> +void qmp_blockdev_insert_medium(const char *device, const char *node_name,
>> +                                Error **errp)
>> +{
>> +    BlockDriverState *bs;
>> +
>> +    bs = bdrv_find_node(node_name);
>> +    if (!bs) {
>> +        error_setg(errp, "Node '%s' not found", node_name);
>> +        return;
>> +    }
> 
> Hmm, it is OK if the bs is not top BDS?

I think so, yes. Generally, there's probably no reason to do that, but I
don't know why we should not allow that case. For instance, you might
want to make a backing file available read-only somewhere.

It should be impossible to make it available writable, and it should not
be allowed to start a block-commit operation while the backing file can
be accessed by the guest, but this should be achieved using op blockers.

What we need for this to work are fine-grained op blockers, I think. But
working around that for now by only allowing to insert top BDS won't
work, since you can still start block jobs which target top BDS, too
(e.g. blockdev-backup can write to a BDS/BB that is visible to the guest).

All in all, I think it's fine to insert non-top BDS, but we should
definitely worry about which exact BDS one can insert once we have
fine-grained op blockers.

Max

> Thanks
> Wen Congyang
> 
>> +
>> +    qmp_blockdev_insert_anon_medium(device, bs, errp);
>> +}
>> +
>>  /* throttling disk I/O limits */
>>  void qmp_block_set_io_throttle(const char *device, int64_t bps, int64_t bps_rd,
>>                                 int64_t bps_wr,
>> diff --git a/qapi/block-core.json b/qapi/block-core.json
>> index 63a83e4..84c9b23 100644
>> --- a/qapi/block-core.json
>> +++ b/qapi/block-core.json
>> @@ -1925,6 +1925,23 @@
>>  { 'command': 'blockdev-remove-medium',
>>    'data': { 'device': 'str' } }
>>  
>> +##
>> +# @blockdev-insert-medium:
>> +#
>> +# Inserts a medium (a block driver state tree) into a block device. That block
>> +# device's tray must currently be open and there must be no medium inserted
>> +# already.
>> +#
>> +# @device:    block device name
>> +#
>> +# @node-name: name of a node in the block driver state graph
>> +#
>> +# Since: 2.5
>> +##
>> +{ 'command': 'blockdev-insert-medium',
>> +  'data': { 'device': 'str',
>> +            'node-name': 'str'} }
>> +
>>  
>>  ##
>>  # @BlockErrorAction
>> diff --git a/qmp-commands.hx b/qmp-commands.hx
>> index ff6c572..b4c34fe 100644
>> --- a/qmp-commands.hx
>> +++ b/qmp-commands.hx
>> @@ -3991,6 +3991,43 @@ Example:
>>  EQMP
>>  
>>      {
>> +        .name       = "blockdev-insert-medium",
>> +        .args_type  = "device:s,node-name:s",
>> +        .mhandler.cmd_new = qmp_marshal_input_blockdev_insert_medium,
>> +    },
>> +
>> +SQMP
>> +blockdev-insert-medium
>> +----------------------
>> +
>> +Inserts a medium (a block driver state tree) into a block device. That block
>> +device's tray must currently be open and there must be no medium inserted
>> +already.
>> +
>> +Arguments:
>> +
>> +- "device": block device name (json-string)
>> +- "node-name": root node of the BDS tree to insert into the block device
>> +
>> +Example:
>> +
>> +-> { "execute": "blockdev-add",
>> +     "arguments": { "options": { "node-name": "node0",
>> +                                 "driver": "raw",
>> +                                 "file": { "driver": "file",
>> +                                           "filename": "fedora.iso" } } } }
>> +
>> +<- { "return": {} }
>> +
>> +-> { "execute": "blockdev-insert-medium",
>> +     "arguments": { "device": "ide1-cd0",
>> +                    "node-name": "node0" } }
>> +
>> +<- { "return": {} }
>> +
>> +EQMP
>> +
>> +    {
>>          .name       = "query-named-block-nodes",
>>          .args_type  = "",
>>          .mhandler.cmd_new = qmp_marshal_input_query_named_block_nodes,
>>
> 



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