The Wednesday 29 Jan 2014 à 13:07:32 (+0800), Fam Zheng wrote :
> This is the common but non-trivial steps to assign or change the
> backing_hd of BDS.
>
> Signed-off-by: Fam Zheng <f...@redhat.com>
> ---
> block.c | 34 +++++++++++++++++++++++++---------
> include/block/block.h | 1 +
> 2 files changed, 26 insertions(+), 9 deletions(-)
>
> diff --git a/block.c b/block.c
> index 8000ac0..c4eaa37 100644
> --- a/block.c
> +++ b/block.c
> @@ -1072,6 +1072,26 @@ fail:
> return ret;
> }
>
> +void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd)
> +{
> + if (bs->backing_hd) {
> + bdrv_unref(bs->backing_hd);
> + }
> +
> + bs->backing_hd = backing_hd;
> + if (!backing_hd) {
> + bs->backing_file[0] = '\0';
> + bs->backing_format[0] = '\0';
> + goto out;
> + }
> + pstrcpy(bs->backing_file, sizeof(bs->backing_file),
> backing_hd->filename);
> + pstrcpy(bs->backing_format, sizeof(bs->backing_file),
I don't understand the sizeof(bs->backing_file). Is it
sizeof(bs->backing_format) ?
> + backing_hd->drv ? backing_hd->drv->format_name : "");
> + bdrv_ref(bs->backing_hd);
> +out:
> + bdrv_refresh_limits(bs);
> +}
> +
> /*
> * Opens the backing file for a BlockDriverState if not yet open
> *
> @@ -1085,6 +1105,7 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict
> *options, Error **errp)
> char backing_filename[PATH_MAX];
> int back_flags, ret;
> BlockDriver *back_drv = NULL;
> + BlockDriverState *backing_hd;
> Error *local_err = NULL;
>
> if (bs->backing_hd != NULL) {
> @@ -1108,7 +1129,7 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict
> *options, Error **errp)
> sizeof(backing_filename));
> }
>
> - bs->backing_hd = bdrv_new("");
> + backing_hd = bdrv_new("");
>
> if (bs->backing_format[0] != '\0') {
> back_drv = bdrv_find_format(bs->backing_format);
> @@ -1118,23 +1139,18 @@ int bdrv_open_backing_file(BlockDriverState *bs,
> QDict *options, Error **errp)
> back_flags = bs->open_flags & ~(BDRV_O_RDWR | BDRV_O_SNAPSHOT |
> BDRV_O_COPY_ON_READ);
>
> - ret = bdrv_open(bs->backing_hd,
> + ret = bdrv_open(backing_hd,
> *backing_filename ? backing_filename : NULL, options,
> back_flags, back_drv, &local_err);
> if (ret < 0) {
> - bdrv_unref(bs->backing_hd);
> - bs->backing_hd = NULL;
> + bdrv_unref(backing_hd);
Here I wonder if this way of calling bdrv_open and doing a bdrv_unref confict
with Max latests bdrv_open patches.
You probably need to rebase and get rid of this bdrv_unref() : check Max series
to be sure.
> bs->open_flags |= BDRV_O_NO_BACKING;
> error_setg(errp, "Could not open backing file: %s",
> error_get_pretty(local_err));
> error_free(local_err);
> return ret;
> }
> -
> - if (bs->backing_hd->file) {
> - pstrcpy(bs->backing_file, sizeof(bs->backing_file),
> - bs->backing_hd->file->filename);
> - }
> + bdrv_set_backing_hd(bs, backing_hd);
>
> /* Recalculate the BlockLimits with the backing file */
> bdrv_refresh_limits(bs);
> diff --git a/include/block/block.h b/include/block/block.h
> index 9125bbe..f449753 100644
> --- a/include/block/block.h
> +++ b/include/block/block.h
> @@ -208,6 +208,7 @@ int bdrv_file_open(BlockDriverState **pbs, const char
> *filename,
> int bdrv_open_image(BlockDriverState **pbs, const char *filename,
> QDict *options, const char *bdref_key, int flags,
> bool force_raw, bool allow_none, Error **errp);
> +void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd);
> int bdrv_open_backing_file(BlockDriverState *bs, QDict *options, Error
> **errp);
> int bdrv_open(BlockDriverState *bs, const char *filename, QDict *options,
> int flags, BlockDriver *drv, Error **errp);
> --
> 1.8.5.3
>
>
bdrv_set_backing_hd seems to be handy since some people want to dynamically
change backing_file using QMP to move them from slow storage to fast storage and
the reverse.
Best regards
Benoît
