Am 25.07.2013 um 16:23 hat Paolo Bonzini geschrieben:
> Define the return value of get_block_status. Bits 0, 1, 2 and 9-62
> are valid; bit 63 (the sign bit) is reserved for errors. Bits 3-8
> are left for future extensions.
>
> The return code is compatible with the old is_allocated API: if a driver
> only returns 0 or 1 (aka BDRV_BLOCK_DATA) like is_allocated used to,
> clients of is_allocated will not have any change in behavior. Still,
> we will return more precise information in the next patches and the
> new definition of bdrv_is_allocated is already prepared for this.
>
> Reviewed-by: Eric Blake <ebl...@redhat.com>
> Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
> ---
> block.c | 10 ++++++++--
> include/block/block.h | 26 ++++++++++++++++++++++++++
> 2 files changed, 34 insertions(+), 2 deletions(-)
>
> diff --git a/block.c b/block.c
> index f533c36..7cfbf71 100644
> --- a/block.c
> +++ b/block.c
> @@ -3004,7 +3004,7 @@ static int64_t coroutine_fn
> bdrv_co_get_block_status(BlockDriverState *bs,
>
> if (!bs->drv->bdrv_co_get_block_status) {
> *pnum = nb_sectors;
> - return 1;
> + return BDRV_BLOCK_DATA;
> }
>
> return bs->drv->bdrv_co_get_block_status(bs, sector_num, nb_sectors,
> pnum);
> @@ -3054,7 +3054,13 @@ int64_t bdrv_get_block_status(BlockDriverState *bs,
> int64_t sector_num,
> int coroutine_fn bdrv_is_allocated(BlockDriverState *bs, int64_t sector_num,
> int nb_sectors, int *pnum)
> {
> - return bdrv_get_block_status(bs, sector_num, nb_sectors, pnum);
> + int64_t ret = bdrv_get_block_status(bs, sector_num, nb_sectors, pnum);
> + if (ret < 0) {
> + return ret;
> + }
> + return
> + (ret & BDRV_BLOCK_DATA) ||
> + ((ret & BDRV_BLOCK_ZERO) && !bdrv_has_zero_init(bs));
> }
>
> /*
> diff --git a/include/block/block.h b/include/block/block.h
> index e41854e..d044b31 100644
> --- a/include/block/block.h
> +++ b/include/block/block.h
> @@ -81,6 +81,32 @@ typedef struct BlockDevOps {
> #define BDRV_SECTOR_SIZE (1ULL << BDRV_SECTOR_BITS)
> #define BDRV_SECTOR_MASK ~(BDRV_SECTOR_SIZE - 1)
>
> +/* BDRV_BLOCK_DATA: data is read from bs->file or another file
> + * BDRV_BLOCK_ZERO: sectors read as zero
> + * BDRV_BLOCK_OFFSET_VALID: sector stored in bs->file as raw data
> + *
> + * If BDRV_BLOCK_OFFSET_VALID is set, bits 9-62 represent the offset in
> + * bs->file where sector data can be read from as raw data.
> + *
> + * DATA == 0 && ZERO == 0 means that data is read from backing_hd if present.
> + *
> + * DATA ZERO OFFSET_VALID
> + * t t t sectors read as zero, bs->file is zero at offset
> + * t f t sectors read as valid from bs->file at offset
> + * f t t sectors preallocated, read as zero, bs->file not
> + * necessarily zero at offset
> + * f f t sectors preallocated but read from backing_hd,
> + * bs->file contains garbage at offset
> + * t t f sectors preallocated, read as zero, unknown offset
> + * t f f sectors read from unknown file or offset
> + * f t f not allocated or unknown offset, read as zero
> + * f f f not allocated or unknown offset, read from
> backing_hd
> + */
> +#define BDRV_BLOCK_DATA 1
> +#define BDRV_BLOCK_ZERO 2
> +#define BDRV_BLOCK_OFFSET_VALID 4
> +#define BDRV_BLOCK_OFFSET_MASK BDRV_SECTOR_MASK
When are block driver supposed to set the BDRV_BLOCK_OFFSET_VALID flag?
For example, qcow2 could in theory set the flag, it has all of the
information already in memory. But with a fragmented image this might
mean that it returns only one cluster instead of a large area with one
bdrv_get_block_status() call.
Should the caller pass a flag that tells whether he is interested in the
offset or not?
Kevin
