Re: [Qemu-devel] [PATCH v6 07/24] block: Convert bdrv_get_block_status() to bytes

[Kevin Wolf <kwolf@redhat.com>]

Am 12.10.2017 um 05:47 hat Eric Blake geschrieben:
> We are gradually moving away from sector-based interfaces, towards
> byte-based.  In the common case, allocation is unlikely to ever use
> values that are not naturally sector-aligned, but it is possible
> that byte-based values will let us be more precise about allocation
> at the end of an unaligned file that can do byte-based access.
> 
> Changing the name of the function from bdrv_get_block_status() to
> bdrv_block_status() ensures that the compiler enforces that all
> callers are updated.  For now, the io.c layer still assert()s that
> all callers are sector-aligned, but that can be relaxed when a later
> patch implements byte-based block status in the drivers.
> 
> There was an inherent limitation in returning the offset via the
> return value: we only have room for BDRV_BLOCK_OFFSET_MASK bits, which
> means an offset can only be mapped for sector-aligned queries (or,
> if we declare that non-aligned input is at the same relative position
> modulo 512 of the answer), so the new interface also changes things to
> return the offset via output through a parameter by reference rather
> than mashed into the return value.  We'll have some glue code that
> munges between the two styles until we finish converting all uses.
> 
> For the most part this patch is just the addition of scaling at the
> callers followed by inverse scaling at bdrv_block_status(), coupled
> with the tweak in calling convention.  But some code, particularly
> bdrv_is_allocated(), gets a lot simpler because it no longer has to
> mess with sectors.
> 
> For ease of review, bdrv_get_block_status_above() will be tackled
> separately.
> 
> Signed-off-by: Eric Blake <eblake@redhat.com>
> 
> ---
> v6: redo interface to return byte-based offset by reference [Kevin]
> v5: drop pointless 'if (pnum)' [John], add comment
> v4: no change
> v3: clamp bytes to 32-bits, rather than asserting
> v2: rebase to earlier changes
> ---
>  include/block/block.h | 17 +++++++++--------
>  block/io.c            | 47 ++++++++++++++++++++++++++++++++++-------------
>  block/qcow2-cluster.c |  2 +-
>  qemu-img.c            | 25 ++++++++++++++-----------
>  4 files changed, 58 insertions(+), 33 deletions(-)
> 
> diff --git a/include/block/block.h b/include/block/block.h
> index 440f3e9e39..7ac851f82f 100644
> --- a/include/block/block.h
> +++ b/include/block/block.h
> @@ -121,7 +121,7 @@ typedef struct HDGeometry {
>  #define BDRV_REQUEST_MAX_BYTES (BDRV_REQUEST_MAX_SECTORS << BDRV_SECTOR_BITS)
> 
>  /*
> - * Allocation status flags for bdrv_get_block_status() and friends.
> + * Allocation status flags for bdrv_block_status() and friends.
>   *
>   * Public flags:
>   * BDRV_BLOCK_DATA: allocation for data at offset is tied to this layer
> @@ -136,10 +136,11 @@ typedef struct HDGeometry {
>   *                 that the block layer recompute the answer from the returned
>   *                 BDS; must be accompanied by just BDRV_BLOCK_OFFSET_VALID.
>   *
> - * If BDRV_BLOCK_OFFSET_VALID is set, bits 9-62 (BDRV_BLOCK_OFFSET_MASK)
> - * represent the offset in the returned BDS that is allocated for the
> - * corresponding raw data; however, whether that offset actually contains
> - * data also depends on BDRV_BLOCK_DATA and BDRV_BLOCK_ZERO, as follows:
> + * If BDRV_BLOCK_OFFSET_VALID is set, bits 9-62 (BDRV_BLOCK_OFFSET_MASK) of
> + * the return value (old interface) or the entire map parameter (new
> + * interface) represent the offset in the returned BDS that is allocated for
> + * the corresponding raw data.

Are there any functions using the old interface left at the end of the
series or do we want a final patch that removes the old interface from
the description?

Kevin