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Re: [PATCH v4 11/16] block/io: support int64_t bytes in bdrv_aligned_pwr

From: Eric Blake
Subject: Re: [PATCH v4 11/16] block/io: support int64_t bytes in bdrv_aligned_pwritev()
Date: Fri, 22 Jan 2021 10:26:31 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0

On 12/11/20 12:39 PM, 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_aligned_pwritev() now and convert the dependencies:
> bdrv_co_write_req_prepare() and bdrv_co_write_req_finish() to signed
> type bytes.
> Conversion of bdrv_co_write_req_prepare() and
> bdrv_co_write_req_finish() is definitely safe, as all requests in
> block/io must not overflow BDRV_MAX_LENGTH. Still add assertions.
> For bdrv_aligned_pwritev() 'bytes' type is widened, so callers are
> safe. Let's check usage of the parameter inside the function.
> Passing to bdrv_co_write_req_prepare() and bdrv_co_write_req_finish()
> is OK.
> Passing to qemu_iovec_* is OK after new assertion. All other callees
> are already updated to int64_t.
> Checking alignment is not changed, offset + bytes and qiov_offset +
> bytes calculations are safe (thanks to new assertions).
> max_transfer is kept to be int for now. It has a default of INT_MAX
> here, and some drivers may rely on it. It's to be refactored later.
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>  block/io.c | 21 +++++++++++++--------
>  1 file changed, 13 insertions(+), 8 deletions(-)

Reviewed-by: Eric Blake <eblake@redhat.com>

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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