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From: Eric Blake <eblake@redhat.com>
To: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Cc: kwolf@redhat.com, ehabkost@redhat.com, qemu-block@nongnu.org,
	qemu-devel@nongnu.org, hreitz@redhat.com, stefanha@redhat.com,
	crosa@redhat.com
Subject: Re: [PATCH 12/12] block-backend: drop INT_MAX restriction from blk_check_byte_request()
Date: Wed, 6 Oct 2021 15:37:51 -0500	[thread overview]
Message-ID: <20211006203751.jhsy424prywt27b3@redhat.com> (raw)
In-Reply-To: <20211006131718.214235-13-vsementsov@virtuozzo.com>

On Wed, Oct 06, 2021 at 03:17:18PM +0200, Vladimir Sementsov-Ogievskiy wrote:
> blk_check_bytes_request is called from blk_co_do_preadv,
> blk_co_do_pwritev_part, blk_co_do_pdiscard and blk_co_copy_range
> before (maybe) calling throttle_group_co_io_limits_intercept() (which
> has int64_t argument) and then calling corresponding bdrv_co_ function.
> bdrv_co_ functions are OK with int64_t bytes as well.
> 
> So dropping the check for INT_MAX we just get same restrictions as in
> bdrv_ layer: discard and write-zeroes goes through
> bdrv_check_qiov_request() and are allowed to be 64bit. Other requests
> go through bdrv_check_request32() and still restricted by INT_MAX
> boundary.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>  block/block-backend.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Deceptively short, but this is the one where a mistake would hurt.

Thankfully, I agree with your analysis that the call stack is still
checking 32-bit limits on read/write, and that discard/zero requests
can now go up to 63-bit sizing if everything else in the call stack is
ready; plus the fact that we are careful both in our drivers to
document actual limits (whether 32-bit or even smaller), and in the
block code to honor those limits (breaking larger requests into chunks
before reaching this far).

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

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org



  reply	other threads:[~2021-10-06 20:39 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-06 13:17 [PATCH 00/12] block: 64bit blk io Vladimir Sementsov-Ogievskiy
2021-10-06 13:17 ` [PATCH 01/12] block-backend: blk_check_byte_request(): int64_t bytes Vladimir Sementsov-Ogievskiy
2021-10-06 15:09   ` Eric Blake
2021-10-06 13:17 ` [PATCH 02/12] block-backend: make blk_co_preadv() 64bit Vladimir Sementsov-Ogievskiy
2021-10-06 15:17   ` Eric Blake
2021-10-06 13:17 ` [PATCH 03/12] block-backend: convert blk_co_pwritev_part to int64_t bytes Vladimir Sementsov-Ogievskiy
2021-10-06 15:25   ` Eric Blake
2021-10-06 13:17 ` [PATCH 04/12] block-backend: convert blk_co_pdiscard " Vladimir Sementsov-Ogievskiy
2021-10-06 15:59   ` Eric Blake
2021-10-06 13:17 ` [PATCH 05/12] block-backend: rename _do_ helper functions to _co_do_ Vladimir Sementsov-Ogievskiy
2021-10-06 16:06   ` Eric Blake
2021-10-06 13:17 ` [PATCH 06/12] block-coroutine-wrapper.py: support BlockBackend first argument Vladimir Sementsov-Ogievskiy
2021-10-06 16:17   ` Eric Blake
2021-10-06 13:17 ` [PATCH 07/12] block-backend: drop blk_prw, use block-coroutine-wrapper Vladimir Sementsov-Ogievskiy
2021-10-06 16:22   ` Eric Blake
2021-10-06 13:17 ` [PATCH 08/12] block-backend: convert blk_foo wrappers to use int64_t bytes parameter Vladimir Sementsov-Ogievskiy
2021-10-06 16:29   ` Eric Blake
2021-10-06 13:17 ` [PATCH 09/12] block-backend: convert blk_co_copy_range to int64_t bytes Vladimir Sementsov-Ogievskiy
2021-10-06 20:04   ` Eric Blake
2021-10-06 13:17 ` [PATCH 10/12] block-backend: convert blk_aio_ functions to int64_t bytes paramter Vladimir Sementsov-Ogievskiy
2021-10-06 20:29   ` Eric Blake
2021-10-12 16:13     ` Vladimir Sementsov-Ogievskiy
2021-10-12 21:37       ` Eric Blake
2021-10-12 21:46         ` Vladimir Sementsov-Ogievskiy
2021-10-06 13:17 ` [PATCH 11/12] block-backend: blk_pread, blk_pwrite: rename count parameter to bytes Vladimir Sementsov-Ogievskiy
2021-10-06 20:33   ` Eric Blake
2021-10-06 13:17 ` [PATCH 12/12] block-backend: drop INT_MAX restriction from blk_check_byte_request() Vladimir Sementsov-Ogievskiy
2021-10-06 20:37   ` Eric Blake [this message]
2021-10-07 17:52 ` [PATCH 13/12] block-backend: fix blk_co_flush prototype to mention coroutine_fn Vladimir Sementsov-Ogievskiy
2021-10-07 20:36   ` Eric Blake
2021-10-07 17:52 ` [PATCH 14/12] block-backend: update blk_co_pwrite() and blk_co_pread() wrappers Vladimir Sementsov-Ogievskiy
2021-10-07 20:38   ` Eric Blake

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