Re: [Qemu-devel] [RFC v2 PATCH 6/6] QAPI: add command for live block commit, 'block-commit'

[Kevin Wolf]

Am 30.08.2012 20:47, schrieb Jeff Cody:
> The command for live block commit is added, which has the following
> arguments:
> 
> device: the block device to perform the commit on (mandatory)
> base:   the base image to commit into; optional (if not specified,
>         it is the underlying original image)
> top:    the top image of the commit - all data from inside top down
>         to base will be committed into base. optional (if not specified,
>         it is the active image) - see note below
> speed:  maximum speed, in bytes/sec
> 
> note: eventually this will support merging down the active layer,
>       but that code is not yet complete.  If the active layer is passed
>       in currently as top, or top is left to the default, then the error
>       QERR_TOP_NOT_FOUND will be returned.
> 
> The is done as a block job, so upon completion a BLOCK_JOB_COMPLETED will
> be emitted.
> 
> Signed-off-by: Jeff Cody <address@hidden>
> ---
>  blockdev.c       | 83 
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  qapi-schema.json | 30 ++++++++++++++++++++
>  qmp-commands.hx  |  6 ++++
>  3 files changed, 119 insertions(+)
> 
> diff --git a/blockdev.c b/blockdev.c
> index 68d65fb..e0d6ca0 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -827,6 +827,89 @@ exit:
>      return;
>  }
>  
> +void qmp_block_commit(const char *device,
> +                      bool has_base, const char *base,
> +                      bool has_top, const char *top,
> +                      bool has_speed, int64_t speed,
> +                      Error **errp)
> +{
> +    BlockDriverState *bs;
> +    BlockDriverState *base_bs, *top_bs, *child_bs;
> +    Error *local_err = NULL;
> +    int orig_base_flags, orig_top_flags;
> +    BlockReopenQueue *reopen_queue = NULL;
> +    /* This will be part of the QMP command, if/when the
> +     * BlockdevOnError change for blkmirror makes it in
> +     */
> +    BlockErrorAction on_error = BLOCK_ERR_REPORT;
> +
> +    /* drain all i/o before commits */
> +    bdrv_drain_all();
> +
> +    bs = bdrv_find(device);
> +    if (!bs) {
> +        error_set(errp, QERR_DEVICE_NOT_FOUND, device);
> +        return;
> +    }
> +    if (base && has_base) {
> +        base_bs = bdrv_find_backing_image(bs, base);
> +    } else {
> +        base_bs = bdrv_find_base(bs);
> +    }
> +
> +    if (base_bs == NULL) {
> +        error_set(errp, QERR_BASE_NOT_FOUND, "NULL");

Shouldn't it be base rather than "NULL"?

> +        return;
> +    }
> +
> +    if (top && has_top) {
> +        /* if we want to allow the active layer,
> +         * use 'bdrv_find_image()' here */
> +        top_bs = bdrv_find_backing_image(bs, top);
> +        if (top_bs == NULL) {
> +            error_set(errp, QERR_TOP_NOT_FOUND, top);
> +            return;
> +        }
> +    } else {
> +        /* we will eventually default to the top layer,i.e. top_bs = bs */
> +        error_set(errp, QERR_TOP_NOT_FOUND, top);
> +        return;
> +    }
> +
> +    child_bs = bdrv_find_child(bs, top_bs);
> +
> +    orig_base_flags = bdrv_get_flags(base_bs);  /* what we are writing into  
>  */
> +    orig_top_flags = bdrv_get_flags(child_bs);  /* to change the backing 
> file */
> +
> +    /* convert base_bs to r/w, if necessary */
> +    if (!(orig_base_flags & BDRV_O_RDWR)) {
> +        reopen_queue = bdrv_reopen_queue(reopen_queue, base_bs,
> +                                         orig_base_flags | BDRV_O_RDWR);
> +    }
> +    if (!(orig_top_flags & BDRV_O_RDWR)) {
> +        reopen_queue = bdrv_reopen_queue(reopen_queue, base_bs,
> +                                         orig_base_flags | BDRV_O_RDWR);

I think you mean child_bs and orig_top_flags. (Why isn't it called
orig_child_flags?)

> +    }
> +    if (reopen_queue) {
> +        bdrv_reopen_multiple(reopen_queue, &local_err);
> +        if (local_err != NULL) {
> +            error_propagate(errp, local_err);
> +            return;
> +        }
> +    }
> +
> +    commit_start(bs, base_bs, top_bs, speed, on_error,
> +                 block_job_cb, bs, orig_base_flags, orig_top_flags,
> +                 &local_err);
> +    if (local_err != NULL) {
> +        error_propagate(errp, local_err);
> +        return;
> +    }
> +    /* Grab a reference so hotplug does not delete the BlockDriverState from
> +     * underneath us.
> +     */
> +    drive_get_ref(drive_get_by_blockdev(bs));
> +}
>  
>  static void eject_device(BlockDriverState *bs, int force, Error **errp)
>  {
> diff --git a/qapi-schema.json b/qapi-schema.json
> index bd8ad74..45feda6 100644
> --- a/qapi-schema.json
> +++ b/qapi-schema.json
> @@ -1401,6 +1401,36 @@
>    'returns': 'str' }
>  
>  ##
> +# @block-commit
> +#
> +# Live commit of data from child image nodes into parent nodes - i.e.,
> +# writes data between 'top' and 'base' into 'base'.
> +#
> +# @device:  the name of the device
> +#
> +# @base:   #optional The parent image of the device to write data into.
> +#                    If not specified, this is the original parent image.

"The file name of the parent image", actually.

Which I'm afraid means that this isn't an API for the long term, but
there's little we can do about it now...

> +#
> +# @top:    #optional The child image, above which data will not be committed
> +#                    down.  If not specified, this is the active layer.

Again, the file name.

Kevin