Re: [Qemu-devel] [PATCH v2 6/7] throttle: Make burst_length 64bit and add range checks

[Eric Blake]

On 08/24/2017 08:24 AM, Alberto Garcia wrote:
> LeakyBucket.burst_length is defined as an unsigned integer but the
> code never checks for overflows and it only makes sure that the value
> is not 0.
> 
> In practice this means that the user can set something like
> throttling.iops-total-max-length=4294967300 despite being larger than
> UINT_MAX and the final value after casting to unsigned int will be 4.
> 
> This patch changes the data type to uint64_t. This does not increase
> the storage size of LeakyBucket, and allows us to assign the value
> directly from qemu_opt_get_number() or BlockIOThrottle and then do the
> checks directly in throttle_is_valid().
> 
> The value of burst_length does not have a specific upper limit,
> but since the bucket size is defined by max * burst_length we have
> to prevent overflows. Instead of going for UINT64_MAX or something
> similar this patch reuses THROTTLE_VALUE_MAX, which allows I/O bursts
> of 1 GiB/s for 10 days in a row.
> 
> Signed-off-by: Alberto Garcia <address@hidden>
> ---
>  include/qemu/throttle.h | 2 +-
>  util/throttle.c         | 5 +++++
>  2 files changed, 6 insertions(+), 1 deletion(-)
> 

Reviewed-by: Eric Blake <address@hidden>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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