Re: [Qemu-devel] [PATCH v2 1/3] monitor: Allow add-fd to any specified fd set

[Eric Blake <eblake@redhat.com>]

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On 10/10/2012 08:20 AM, Corey Bryant wrote:
> The first call to add an fd to an fd set was previously not
> allowed to choose the fd set ID.  The ID was generated as
> the first available and ensuing calls could add more fds by
> specifying the fd set ID.  This change allows users to
> choose the fd set ID on the first call.

Unfortunately, it now allows the user to choose arbitrary integer set
ids with large gaps, where previously, the user could only influence set
ids by populating all intermediate ids.  That is, before this patch, a
user would have to create 1000000 sets to have an id of 1000000 (if they
didn't run out of memory first on all the earlier sets), but now they
can have an id that large with just one set.  Or, taken further,
previously, a user request of -9223372036854775808 would likely fail (if
not, how beefy is your machine?), but now it can succeed and cause
confusion because of integer wraparound.  Arbitrary set ids is not
necessarily bad, but I think you need to add bounds-checking on the
user's requested fdset_id to make sure it is positive.

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


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