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Re: [Qemu-devel] [Nbd] [PATCH] nbd: fix trim/discard commands with a len

From: Alex Bligh
Subject: Re: [Qemu-devel] [Nbd] [PATCH] nbd: fix trim/discard commands with a length bigger than NBD_MAX_BUFFER_SIZE
Date: Tue, 10 May 2016 16:41:27 +0100

On 10 May 2016, at 16:29, Eric Blake <address@hidden> wrote:

> So the kernel is currently one of the clients that does NOT honor block
> sizes, and as such, servers should be prepared for ANY size up to
> UINT_MAX (other than DoS handling).

Interesting followup question:

If the kernel does not fragment TRIM requests at all (in the
same way it fragments read and write requests), I suspect
something bad may happen with TRIM requests over 2^31
in size (particularly over 2^32 in size), as the length
field in nbd only has 32 bits.

Whether it supports block size constraints or not, it is
going to need to do *some* breaking up of requests.

Alex Bligh

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