Messages in this thread Patch in this message | | | From | Dave Chinner <> | Subject | [PATCH 3/6] Extend completions to provide XFS object flush requirements | Date | Fri, 27 Jun 2008 18:44:41 +1000 |
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XFS object flushing doesn't quite match existing completion semantics. It mixed exclusive access with completion. That is, we need to mark an object as being flushed before flushing it to disk, and then block any other attempt to flush it until the completion occurs. We do this but adding an extra count to the completion before we start using them. However, we still need to determine if there is a completion in progress, and allow no-blocking attempts fo completions to decrement the count.
To do this we introduce:
int try_wait_for_completion(struct completion *x) returns a failure status if done == 0, otherwise decrements done to zero and returns a "started" status. This is provided to allow counted completions to begin safely while holding object locks in inverted order.
int completion_done(struct completion *x) returns 1 if there is no waiter, 0 if there is a waiter (i.e. a completion in progress).
This replaces the use of semaphores for providing this exclusion and completion mechanism.
Version 2: o remove "flush" based API and just add the minimum necessary extensions to allow counting completions to do what is needed by XFS. o docbook format comments
Signed-off-by: Dave Chinner <david@fromorbit.com> --- include/linux/completion.h | 45 ++++++++++++++++++++++++++++++++++++++++++++ 1 files changed, 45 insertions(+), 0 deletions(-)
diff --git a/include/linux/completion.h b/include/linux/completion.h index d2961b6..57faa60 100644 --- a/include/linux/completion.h +++ b/include/linux/completion.h @@ -55,4 +55,49 @@ extern void complete_all(struct completion *); #define INIT_COMPLETION(x) ((x).done = 0) + +/** + * try_wait_for_completion - try to decrement a completion without blocking + * @x: completion structure + * + * Returns: 0 if a decrement cannot be done without blocking + * 1 if a decrement succeeded. + * + * If a completion is being used as a counting completion, + * attempt to decrement the counter without blocking. This + * enables us to avoid waiting if the resource the completion + * is protecting is not available. + */ +static inline bool try_wait_for_completion(struct completion *x) +{ + int ret = 1; + + spin_lock_irq(&x->wait.lock); + if (!x->done) + ret = 0; + else + x->done--; + spin_unlock_irq(&x->wait.lock); + return ret; +} + +/** + * completion_done - Test to see if a completion has any waiters + * @x: completion structure + * + * Returns: 0 if there are waiters (wait_for_completion() in progress) + * 1 if there are no waiters. + * + */ +static inline bool completion_done(struct completion *x) +{ + int ret = 1; + + spin_lock_irq(&x->wait.lock); + if (!x->done) + ret = 0; + spin_unlock_irq(&x->wait.lock); + return ret; +} + #endif -- 1.5.5.4
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