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Date: Fri, 6 Feb 2015 14:59:24 +0300
From: "Denis V. Lunev" <den@openvz.org>
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Subject: Re: [Qemu-devel] [PATCH 1/1] nbd: fix
	max_discard/max_transfer_length
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To: Kevin Wolf <kwolf@redhat.com>
Cc: Peter Lieven <pl@kamp.de>, qemu-devel@nongnu.org

On 06/02/15 14:53, Kevin Wolf wrote:
> Am 06.02.2015 um 12:24 hat Denis V. Lunev geschrieben:
>> nbd_co_discard calls nbd_client_session_co_discard which uses uint32_t
>> as the length in bytes of the data to discard due to the following
>> definition:
>>
>> struct nbd_request {
>>      uint32_t magic;
>>      uint32_t type;
>>      uint64_t handle;
>>      uint64_t from;
>>      uint32_t len; <-- the length of data to be discarded, in bytes
>> } QEMU_PACKED;
>>
>> Thus we should limit bl_max_discard to UINT32_MAX >> BDRV_SECTOR_BITS to
>> avoid overflow.
>>
>> NBD read/write code uses the same structure for transfers. Fix
>> max_transfer_length accordingly.
>>
>> Signed-off-by: Denis V. Lunev <den@openvz.org>
>> CC: Peter Lieven <pl@kamp.de>
>> CC: Kevin Wolf <kwolf@redhat.com>
> Thanks, I have applied both Peter's and your patch. Can you guys please
> check whether the current state of my block branch is correct or whether
> I forgot to include or remove some patch?
can you give me tree URL?

> By the way, I don't think this NBD patch is strictly necessary as you'll
> have a hard time finding a platform where INT_MAX > UINT32_MAX, but I
> think it's good documentation at least and a safeguard if we ever decide
> to lift the general block layer restrictions.
>
> Kevin
nope, it is absolutely mandatory

stdint.h:

/* Limit of `size_t' type.  */
# if __WORDSIZE == 64
#  define SIZE_MAX              (18446744073709551615UL)
# else
#  define SIZE_MAX              (4294967295U)
# endif

Den