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Re: [Qemu-devel] [PATCHv5] block/get_block_status: avoid redundant callo
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCHv5] block/get_block_status: avoid redundant callouts on raw devices |
Date: |
Mon, 07 Oct 2013 10:25:57 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130923 Thunderbird/17.0.9 |
Il 07/10/2013 07:59, Peter Lieven ha scritto:
> if a raw device like an iscsi target or host device is used
> the current implementation makes a second call out to get
> the block status of bs->file.
>
> Signed-off-by: Peter Lieven <address@hidden>
> ---
> v5: add a generic get_lba_status function in the raw driver which
> adds the BDRV_BLOCK_RAW flag. bdrv_co_get_block_status will
> handle the callout to bs->file then.
>
> v4: use a flag to detect the raw driver instead of the strncmp
> hack
>
> block.c | 4 ++++
> block/raw_bsd.c | 3 ++-
> include/block/block.h | 4 ++++
> 3 files changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/block.c b/block.c
> index 93e113a..38a589e 100644
> --- a/block.c
> +++ b/block.c
> @@ -3147,6 +3147,10 @@ static int64_t coroutine_fn
> bdrv_co_get_block_status(BlockDriverState *bs,
> return ret;
> }
>
> + if (ret & BDRV_BLOCK_RAW) {
> + return bdrv_get_block_status(bs->file, sector_num, nb_sectors, pnum);
Strictly speaking, this should probably do something like this:
assert(ret & BDRV_BLOCK_OFFSET_VALID);
return bdrv_get_block_status(bs->file, ret >> BDRV_SECTOR_BITS,
nb_sectors, pnum);
Or alternatively the raw driver should return just "BDRV_BLOCK_RAW".
As a third option, the raw driver could also return not just
BDRV_BLOCK_RAW and BDRV_BLOCK_OFFSET_VALID, but also BDRV_BLOCK_DATA (so
that the answer makes some sense even without going down to bs->file).
But I'll let the block maintainers decide what to do.
Paolo
> + }
> +
> if (!(ret & BDRV_BLOCK_DATA)) {
> if (bdrv_has_zero_init(bs)) {
> ret |= BDRV_BLOCK_ZERO;
> diff --git a/block/raw_bsd.c b/block/raw_bsd.c
> index d4ace60..308d605 100644
> --- a/block/raw_bsd.c
> +++ b/block/raw_bsd.c
> @@ -62,7 +62,8 @@ static int64_t coroutine_fn
> raw_co_get_block_status(BlockDriverState *bs,
> int64_t sector_num,
> int nb_sectors, int *pnum)
> {
> - return bdrv_get_block_status(bs->file, sector_num, nb_sectors, pnum);
> + return BDRV_BLOCK_RAW | BDRV_BLOCK_OFFSET_VALID |
> + (sector_num << BDRV_SECTOR_BITS);
> }
>
> static int coroutine_fn raw_co_write_zeroes(BlockDriverState *bs,
> diff --git a/include/block/block.h b/include/block/block.h
> index f808550..003699e 100644
> --- a/include/block/block.h
> +++ b/include/block/block.h
> @@ -84,6 +84,9 @@ typedef struct BlockDevOps {
> /* 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
> + * BDRV_BLOCK_RAW: used internally to indicate that the request
> + * was answered by the raw driver and that one
> + * should look in bs->file directly.
> *
> * 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.
> @@ -105,6 +108,7 @@ typedef struct BlockDevOps {
> #define BDRV_BLOCK_DATA 1
> #define BDRV_BLOCK_ZERO 2
> #define BDRV_BLOCK_OFFSET_VALID 4
> +#define BDRV_BLOCK_RAW 8
> #define BDRV_BLOCK_OFFSET_MASK BDRV_SECTOR_MASK
>
> typedef enum {
>