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

From: Kevin Wolf
Subject: Re: [Qemu-devel] [PATCH 1/1] nbd: fix max_discard/max_transfer_length
Date: Fri, 6 Feb 2015 12:53:47 +0100
User-agent: Mutt/1.5.21 (2010-09-15)

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
> 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 <address@hidden>
> CC: Peter Lieven <address@hidden>
> CC: Kevin Wolf <address@hidden>

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?

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.


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