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| author | Nick Piggin <nickpiggin@yahoo.com.au> | 2005-11-13 16:07:25 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@g5.osdl.org> | 2005-11-13 18:14:16 -0800 |
| commit | 8426e1f6af0fd7f44d040af7263750c5a52f3cc3 (patch) | |
| tree | 827bd2588c2b73d11cea6869de8ff42dba134375 /Documentation/atomic_ops.txt | |
| parent | 4a6dae6d382e9edf3ff440b819e554ed706359bc (diff) | |
| download | lwn-8426e1f6af0fd7f44d040af7263750c5a52f3cc3.tar.gz lwn-8426e1f6af0fd7f44d040af7263750c5a52f3cc3.zip | |
[PATCH] atomic: inc_not_zero
Introduce an atomic_inc_not_zero operation. Make this a special case of
atomic_add_unless because lockless pagecache actually wants
atomic_inc_not_negativeone due to its offset refcount.
Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'Documentation/atomic_ops.txt')
| -rw-r--r-- | Documentation/atomic_ops.txt | 14 |
1 files changed, 13 insertions, 1 deletions
diff --git a/Documentation/atomic_ops.txt b/Documentation/atomic_ops.txt index f1744161ef06..23a1c2402bcc 100644 --- a/Documentation/atomic_ops.txt +++ b/Documentation/atomic_ops.txt @@ -115,7 +115,7 @@ boolean is return which indicates whether the resulting counter value is negative. It requires explicit memory barrier semantics around the operation. -Finally: +Then: int atomic_cmpxchg(atomic_t *v, int old, int new); @@ -129,6 +129,18 @@ atomic_cmpxchg requires explicit memory barriers around the operation. The semantics for atomic_cmpxchg are the same as those defined for 'cas' below. +Finally: + + int atomic_add_unless(atomic_t *v, int a, int u); + +If the atomic value v is not equal to u, this function adds a to v, and +returns non zero. If v is equal to u then it returns zero. This is done as +an atomic operation. + +atomic_add_unless requires explicit memory barriers around the operation. + +atomic_inc_not_zero, equivalent to atomic_add_unless(v, 1, 0) + If a caller requires memory barrier semantics around an atomic_t operation which does not return a value, a set of interfaces are |