Re: [Qemu-block] [Qemu-devel] [PATCH 1/2] qemu-io: don't allow I/O operations larger than INT_MAX

[Alberto Garcia]

On Tue 31 Jan 2017 05:41:23 PM CET, Eric Blake <address@hidden> wrote:

>>> Ideally, it would be nice to fix the block layer to allow larger
>>> requests (since we already have code to auto-fragment down to device
>>> limits, we should be able to rely on that code instead of having to
>>> duplicate artificial constraints everywhere else in the tree).  But
>>> that's a bigger task, and this is a good patch in the interim.
>> 
>> Related question: what's the largest request than a guest can
>> theoretically submit?
>
> off_t supports up to 2^63 (not 2^64, because it is a signed type).
> Ideally, we should be constrained only by the disk size (as no one
> actually has 2^63 bytes of storage available), by using uint64_t
> offset AND length in all our APIs; but right now, we still have a lot
> of 32-bit length issues, and often signed length limiting us to 2^31
> depending on the API.

My question was more like: what happens if the guest submits a request
with the maximum possible size? Does QEMU handle that correctly?

Berto