Re: [PATCH v3 05/17] block/io: support int64_t bytes in bdrv_co_do_pwrite_zeroes()

[Eric Blake <eblake@redhat.com>]

On 4/30/20 6:10 AM, Vladimir Sementsov-Ogievskiy wrote:
> We are generally moving to int64_t for both offset and bytes parameters
> on all io paths.
> 
> Main motivation is realization of 64-bit write_zeroes operation for
> fast zeroing large disk chunks, up to the whole disk.
> 
> We chose signed type, to be consistent with off_t (which is signed) and
> with possibility for signed return type (where negative value means
> error).
> 
> So, prepare bdrv_co_do_pwrite_zeroes() now.
> 
> Patch-correctness audit by Eric Blake:
> 

> 
>      use of 'num' within the loop
>      compute 'int head' via % 'int alignment' - safe
>      clamp size by 'int max_write_zeroes' - safe
>      drv->bdrv_co_pwrite_zeroes(int) - safe because of clamping
>      clamp size by 'int max_transfer' - safe
>      qemu_iovec_init_buf(size_t) - safe because of clamping
>      bdrv_driver_pwritev(uint64_t) [well, int64_t after 4/17] - safe

I know you were quoting me, but the [comment] can be dropped (I wrote my 
audit on patches in isolation while reviewing the pre-series state of 
the tree, but when this commit is finally applied, the previous patch 
will already be in place)

> 
>      So even with the wider type, we aren't exceeding the contract of
>      anything we pass it on to.  Later patches may improve
>      drv->bdrv_co_pwrite_zeroes and qemu_iovec_init_buf to be 64-bit
>      clean, at which point we would want to revisit this function to use
>      64-bit clamping rather than 32-bit clamping, but it does not have
>      to happen here.
> 
> Series: 64bit-block-status
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> Reviewed-by: Eric Blake <eblake@redhat.com>
> ---
>   block/io.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
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