take read_seqbegin_or_lock() and friends to seqlock.h

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 29 insertions, 0 deletions

diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
index 1e8a8b6e837d..cf87a24c0f92 100644
--- a/include/linux/seqlock.h
+++ b/include/linux/seqlock.h
@@ -354,6 +354,35 @@ static inline void read_sequnlock_excl(seqlock_t *sl)
         spin_unlock(&sl->lock);
 }
 
+/**
+ * read_seqbegin_or_lock - begin a sequence number check or locking block
+ * @lock: sequence lock
+ * @seq : sequence number to be checked
+ *
+ * First try it once optimistically without taking the lock. If that fails,
+ * take the lock. The sequence number is also used as a marker for deciding
+ * whether to be a reader (even) or writer (odd).
+ * N.B. seq must be initialized to an even number to begin with.
+ */
+static inline void read_seqbegin_or_lock(seqlock_t *lock, int *seq)
+{
+        if (!(*seq & 1))        /* Even */
+                *seq = read_seqbegin(lock);
+        else                    /* Odd */
+                read_seqlock_excl(lock);
+}
+
+static inline int need_seqretry(seqlock_t *lock, int seq)
+{
+        return !(seq & 1) && read_seqretry(lock, seq);
+}
+
+static inline void done_seqretry(seqlock_t *lock, int seq)
+{
+        if (seq & 1)
+                read_sequnlock_excl(lock);
+}
+
 static inline void read_seqlock_excl_bh(seqlock_t *sl)
 {
         spin_lock_bh(&sl->lock);