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

[Eric Blake]

On 01/31/2017 10:36 AM, Alberto Garcia wrote:
> On Tue 31 Jan 2017 05:31:32 PM CET, Eric Blake 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.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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