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authorDavid Chinner <david@fromorbit.com>2008-08-13 02:40:43 -0400
committerLachlan McIlroy <lachlan@redback.melbourne.sgi.com>2008-08-13 02:40:43 -0400
commit39d2f1ab2a36ac527a6c41cfe689f50c239eaca3 (patch)
tree47ee9ab904387a2062705c69197725596e6b2661 /include
parentb4dd330b9e0c9c78ebff754e72563b148f05e9e0 (diff)
[XFS] extend completions to provide XFS object flush requirements
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. SGI-PV: 981498 SGI-Modid: xfs-linux-melb:xfs-kern:31816a Signed-off-by: David Chinner <david@fromorbit.com> Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
Diffstat (limited to 'include')
-rw-r--r--include/linux/completion.h45
1 files changed, 45 insertions, 0 deletions
diff --git a/include/linux/completion.h b/include/linux/completion.h
index d2961b66d53d..57faa60de9bd 100644
--- a/include/linux/completion.h
+++ b/include/linux/completion.h
@@ -55,4 +55,49 @@ extern void complete_all(struct completion *);
55 55
56#define INIT_COMPLETION(x) ((x).done = 0) 56#define INIT_COMPLETION(x) ((x).done = 0)
57 57
58
59/**
60 * try_wait_for_completion - try to decrement a completion without blocking
61 * @x: completion structure
62 *
63 * Returns: 0 if a decrement cannot be done without blocking
64 * 1 if a decrement succeeded.
65 *
66 * If a completion is being used as a counting completion,
67 * attempt to decrement the counter without blocking. This
68 * enables us to avoid waiting if the resource the completion
69 * is protecting is not available.
70 */
71static inline bool try_wait_for_completion(struct completion *x)
72{
73 int ret = 1;
74
75 spin_lock_irq(&x->wait.lock);
76 if (!x->done)
77 ret = 0;
78 else
79 x->done--;
80 spin_unlock_irq(&x->wait.lock);
81 return ret;
82}
83
84/**
85 * completion_done - Test to see if a completion has any waiters
86 * @x: completion structure
87 *
88 * Returns: 0 if there are waiters (wait_for_completion() in progress)
89 * 1 if there are no waiters.
90 *
91 */
92static inline bool completion_done(struct completion *x)
93{
94 int ret = 1;
95
96 spin_lock_irq(&x->wait.lock);
97 if (!x->done)
98 ret = 0;
99 spin_unlock_irq(&x->wait.lock);
100 return ret;
101}
102
58#endif 103#endif