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From: Paolo Bonzini <pbonzini@redhat.com>
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Date: Fri, 4 Mar 2016 10:12:19 +0100
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Subject: Re: [Qemu-devel] [PATCH] rng: switch request queue to QSIMPLEQ
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To: Ladi Prosek <lprosek@redhat.com>, Amit Shah <amit.shah@redhat.com>
Cc: pagupta <pagupta@redhat.com>, qemu-devel@nongnu.org



On 04/03/2016 09:04, Ladi Prosek wrote:
>>> >> +    QSIMPLEQ_INIT(&s->requests);
>>> >>  }
>> >
>> > This init here isn't necessary, the accessors for the queue will take
>> > care of this.
> We are basically purging the queue here and we want to leave it in a
> consistent state. Without the QSIMPLEQ_INIT the queue head would
> become a pair of dangling pointers. Let me know if I misunderstood
> your comment.

It wouldn't, check out QSIMPLEQ_REMOVE_HEAD:

#define QSIMPLEQ_REMOVE_HEAD(head, field) do {
    if (((head)->sqh_first = (head)->sqh_first->field.sqe_next) == NULL)
        (head)->sqh_last = &(head)->sqh_first;
} while (/*CONSTCOND*/0)

The queue would become { NULL, &s->requests.sqh_first }.  So the
QSIMPLEQ_INIT is indeed redundant.

Paolo