Re: [Qemu-devel] [PATCH v2 3/6] qemu-img: Implement commit like QMP

[Kevin Wolf <kwolf@redhat.com>]

Am 08.04.2014 um 14:50 hat Max Reitz geschrieben:
> qemu-img should use QMP commands whenever possible in order to ensure
> feature completeness of both online and offline image operations. As
> qemu-img itself has no access to QMP (since this would basically require
> just everything being linked into qemu-img), imitate QMP's
> implementation of block-commit by using commit_active_start() and then
> waiting for the block job to finish.

Leaves us with the HMP commit command that uses the old bdrv_commit()
function. I wonder if we can get rid of it by letting the HMP command
stop the VM, do a live commit, and then restart the VM.

> This new implementation does not empty the snapshot image, as opposed to
> the old implementation using bdrv_commit(). However, as QMP's
> block-commit apparently never did this and as qcow2 (which is probably
> qemu's standard image format) does not even implement the required
> function (bdrv_make_empty()), it does not seem necessary.

In fact, I think since qcow2 has discard support it would actually be
possible to write a sensible implementation of bdrv_make_empty(). That's
a separate feature, though, and can go in a different patch series.

> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  block/Makefile.objs |  2 +-
>  qemu-img.c          | 70 ++++++++++++++++++++++++++++++++++++++---------------
>  2 files changed, 52 insertions(+), 20 deletions(-)
> 
> diff --git a/block/Makefile.objs b/block/Makefile.objs
> index fd88c03..2c37e80 100644
> --- a/block/Makefile.objs
> +++ b/block/Makefile.objs
> @@ -9,6 +9,7 @@ block-obj-y += snapshot.o qapi.o
>  block-obj-$(CONFIG_WIN32) += raw-win32.o win32-aio.o
>  block-obj-$(CONFIG_POSIX) += raw-posix.o
>  block-obj-$(CONFIG_LINUX_AIO) += linux-aio.o
> +block-obj-y += mirror.o
>  
>  ifeq ($(CONFIG_POSIX),y)
>  block-obj-y += nbd.o nbd-client.o sheepdog.o
> @@ -22,7 +23,6 @@ endif
>  
>  common-obj-y += stream.o
>  common-obj-y += commit.o
> -common-obj-y += mirror.o
>  common-obj-y += backup.o
>  
>  iscsi.o-cflags     := $(LIBISCSI_CFLAGS)
> diff --git a/qemu-img.c b/qemu-img.c
> index 8455994..e86911f 100644
> --- a/qemu-img.c
> +++ b/qemu-img.c
> @@ -30,6 +30,7 @@
>  #include "qemu/osdep.h"
>  #include "sysemu/sysemu.h"
>  #include "block/block_int.h"
> +#include "block/blockjob.h"
>  #include "block/qapi.h"
>  #include <getopt.h>
>  
> @@ -682,12 +683,37 @@ fail:
>      return ret;
>  }
>  
> +static void dummy_block_job_cb(void *opaque, int ret)
> +{
> +}

Why don't we need to check the return value?

Kevin