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    SubjectRe: wait_event_interruptible_timeout
    On 09/24, Ani Sinha wrote:
    > I have noticed an issue with wait_event_interruptible_timeout() API
    > which I will try to explain below:
    > wait_event_interruptible_timeout() is supposed to wait until one of
    > the following happens:
    > (a) Timeout occurs (with no signals or the event of interest
    > happening), in which case it returns 0
    > (b) The process receives a signal and wakes up prematurely (i.e.,
    > before its timeout expired or the event of interest occurred). In this
    > case, it returns ?ERESTARTSYS. I will come back to this later.
    > (c) Of course, the last obvious way to wake up is that the event of
    > interest occurs and it wakes up all (or one) process on the wait
    > queue. In that case, it returns the # of jiffies that is left before
    > the timeout would have occurred (unslept or balance jiffies).
    > What if I really wanted to sleep for timeout interval and no more?
    > That is to say, if I wake up on a signal and I wanted to know how many
    > jiffies I did used up while sleeping and how many I am left with (just
    > like poll or select does)?

    You can read jiffies before and after wait_event_interruptible_timeout().

    > That way, when I retry the API, I can tell
    > it to sleep only by the amount of my balance sleeping time.

    Something like

    unsigned long now = jiffies;
    ret = wait_event_interruptible_timeout(..., timeout);
    if (ret < 0) {
    next_timeout = now + timeout - jiffies;
    if (next_timeout < 0)
    next_timeout = 0;

    We can even add another wait_ helper which treats "timeout" as lvalue
    and updates it before return. I dunno.

    > Unfortunately, the interface looses this information since it
    > overrides the return value with ERESTARTSYS.

    Yes you are right, but

    > I feel there is a need to
    > modify the code in order to correct this behavior.

    I'm afraid it would be a pain to modify this API. But please
    do not hesitate to make the patch if you think the current API
    can be improved. At worst, the patch will be nacked ;)


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      Last update: 2008-09-25 18:43    [W:0.029 / U:7.024 seconds]
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