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Re: [Qemu-block] [PATCH 11/27] block: x-blockdev-create QMP command

From: Eric Blake
Subject: Re: [Qemu-block] [PATCH 11/27] block: x-blockdev-create QMP command
Date: Thu, 15 Feb 2018 13:58:50 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0

On 02/08/2018 01:23 PM, Kevin Wolf wrote:
This adds a synchronous x-blockdev-create QMP command that can create
qcow2 images on a given node name.

We don't want to block while creating an image, so this is not the final
interface in all aspects, but BlockdevCreateOptionsQcow2 and
.bdrv_co_create() are what they actually might look like in the end. In
any case, this should be good enough to test whether we interpret
BlockdevCreateOptions as we should.

Signed-off-by: Kevin Wolf <address@hidden>

@@ -3442,6 +3442,18 @@
    } }
+# @x-blockdev-create:
+# Create an image format on a given node.
+# TODO Replace with something asynchronous (block job?)

We've learned our lesson - don't commit to the final name on an interface that we have not yet experimented with.

+# Since: 2.12
+{ 'command': 'x-blockdev-create',
+  'data': 'BlockdevCreateOptions',
+  'boxed': true }

Lots of code packed in that little description ;)

+++ b/include/block/block_int.h
@@ -130,6 +130,8 @@ struct BlockDriver {
      int (*bdrv_file_open)(BlockDriverState *bs, QDict *options, int flags,
                            Error **errp);
      void (*bdrv_close)(BlockDriverState *bs);
+    int coroutine_fn (*bdrv_co_create)(BlockdevCreateOptions *opts,
+                                       Error **errp);

I know we haven't been very good in the past, but can you add a comment here on the contract that drivers are supposed to obey when implementing this callback?

+++ b/block.c
@@ -369,7 +369,7 @@ BlockDriver *bdrv_find_format(const char *format_name)
      return bdrv_do_find_format(format_name);
-static int bdrv_is_whitelisted(BlockDriver *drv, bool read_only)
+int bdrv_is_whitelisted(BlockDriver *drv, bool read_only)

Worth mentioning that bdrv_is_whitelisted had to be exported as part of the commit message? (Or even promoting it to public in a separate commit?)

+++ b/block/create.c
@@ -0,0 +1,75 @@
+ * Block layer code related to image creation
+ *
+ * Copyright (c) 2018 Kevin Wolf <address@hidden>

The question came up in another thread, but I didn't hear your answer there; I know Red Hat permits you to claim personal copyright while still using a redhat.com address for code written on personal time, but should this claim belong to Red Hat instead of you?

+    /* Call callback if it exists */
+    if (!drv->bdrv_co_create) {
+        error_setg(errp, "Driver does not support blockdev-create");

Should this error message refer to 'x-blockdev-create' in the short term?

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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