Re: [Qemu-devel] [PATCH 1/1] nbd: fix max_discard/max_transfer_length

[Peter Lieven <pl@kamp.de>]

Am 06.02.2015 um 12:59 schrieb Denis V. Lunev:
> 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
Yes, but we limit to MIN(SIZE_MAX >> BDRV_SECTOR_BITS, INT_MAX >> BDRV_SECTOR_BITS) anyway.

I do not know if there is a platform where INT_MAX is 2^63 - 1 and not 2^31 - 1 ?

We can keep Dens patch in. Just in case. It doesn't hurt.

Peter