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Re: [libvirt] [PATCH 12/23] Add JSON serialization of virLockSpacePtr objects for process re-exec()



On 08/16/2012 05:07 PM, Eric Blake wrote:
> On 08/09/2012 09:20 AM, Daniel P. Berrange wrote:
>> From: "Daniel P. Berrange" <berrange redhat com>
>>
>> Add two new APIs virLockSpaceNewPostExecRestart and
>> virLockSpacePreExecRestart which allow a virLockSpacePtr
>> object to be created from a JSON object and saved to a
>> JSON object, for the purposes of re-exec'ing a process.
>>
>> As well as saving the state in JSON format, the second
>> method will disable the O_CLOEXEC flag so that the open
>> file descriptors are preserved across the process re-exec()
>>
>> Signed-off-by: Daniel P. Berrange <berrange redhat com>
>> ---
> 
> Is virLockSpacePreExecRestart called in the parent prior to forking
> (mostly good, with one caveat) or in the child between fork and exec
> (bad, since you malloc and do a lot of other non-async-safe stuff)?  If
> the latter, we risk deadlock; if the former, then you have at least one
> bug...

Before you worry about responding to this, read my comments on 21/23.  I
think I've managed to convince myself that if these functions are only
ever called from virtlockd (and _not_ from libvirt.so or libvirtd), then
the fact that virtlockd is so dedicated-purpose as to never spawn a
helper child means that you don't have to worry about FD_CLOEXEC races
to arbitrary children.  If you agree with my analysis, then this patch
(and several like it where I complained about CLOEXEC races) should be
okay as-is.

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

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