xarray: Add XArray conditional store operations

Like cmpxchg(), xa_cmpxchg will only store to the index if the current
entry matches the old entry.  It returns the current entry, which is
usually more useful than the errno returned by radix_tree_insert().
For the users who really only want the errno, the xa_insert() wrapper
provides a more convenient calling convention.

Signed-off-by: Matthew Wilcox <willy@infradead.org>

1 files changed, 60 insertions, 0 deletions

diff --git a/include/linux/xarray.h b/include/linux/xarray.h
index 15eab63286ed..7f740f675b96 100644
--- a/include/linux/xarray.h
+++ b/include/linux/xarray.h
@@ -275,6 +275,8 @@ struct xarray {
 void xa_init_flags(struct xarray *, gfp_t flags);
 void *xa_load(struct xarray *, unsigned long index);
 void *xa_store(struct xarray *, unsigned long index, void *entry, gfp_t);
+void *xa_cmpxchg(struct xarray *, unsigned long index,
+			void *old, void *entry, gfp_t);
 bool xa_get_mark(struct xarray *, unsigned long index, xa_mark_t);
 void xa_set_mark(struct xarray *, unsigned long index, xa_mark_t);
 void xa_clear_mark(struct xarray *, unsigned long index, xa_mark_t);
@@ -334,6 +336,34 @@ static inline void *xa_erase(struct xarray *xa, unsigned long index)
 	return xa_store(xa, index, NULL, 0);
 }
 
+/**
+ * xa_insert() - Store this entry in the XArray unless another entry is
+ *			already present.
+ * @xa: XArray.
+ * @index: Index into array.
+ * @entry: New entry.
+ * @gfp: Memory allocation flags.
+ *
+ * If you would rather see the existing entry in the array, use xa_cmpxchg().
+ * This function is for users who don't care what the entry is, only that
+ * one is present.
+ *
+ * Context: Process context.  Takes and releases the xa_lock.
+ *	    May sleep if the @gfp flags permit.
+ * Return: 0 if the store succeeded.  -EEXIST if another entry was present.
+ * -ENOMEM if memory could not be allocated.
+ */
+static inline int xa_insert(struct xarray *xa, unsigned long index,
+		void *entry, gfp_t gfp)
+{
+	void *curr = xa_cmpxchg(xa, index, NULL, entry, gfp);
+	if (!curr)
+		return 0;
+	if (xa_is_err(curr))
+		return xa_err(curr);
+	return -EEXIST;
+}
+
 #define xa_trylock(xa)		spin_trylock(&(xa)->xa_lock)
 #define xa_lock(xa)		spin_lock(&(xa)->xa_lock)
 #define xa_unlock(xa)		spin_unlock(&(xa)->xa_lock)
@@ -355,10 +385,40 @@ static inline void *xa_erase(struct xarray *xa, unsigned long index)
  */
 void *__xa_erase(struct xarray *, unsigned long index);
 void *__xa_store(struct xarray *, unsigned long index, void *entry, gfp_t);
+void *__xa_cmpxchg(struct xarray *, unsigned long index, void *old,
+		void *entry, gfp_t);
 void __xa_set_mark(struct xarray *, unsigned long index, xa_mark_t);
 void __xa_clear_mark(struct xarray *, unsigned long index, xa_mark_t);
 
 /**
+ * __xa_insert() - Store this entry in the XArray unless another entry is
+ *			already present.
+ * @xa: XArray.
+ * @index: Index into array.
+ * @entry: New entry.
+ * @gfp: Memory allocation flags.
+ *
+ * If you would rather see the existing entry in the array, use __xa_cmpxchg().
+ * This function is for users who don't care what the entry is, only that
+ * one is present.
+ *
+ * Context: Any context.  Expects xa_lock to be held on entry.  May
+ *	    release and reacquire xa_lock if the @gfp flags permit.
+ * Return: 0 if the store succeeded.  -EEXIST if another entry was present.
+ * -ENOMEM if memory could not be allocated.
+ */
+static inline int __xa_insert(struct xarray *xa, unsigned long index,
+		void *entry, gfp_t gfp)
+{
+	void *curr = __xa_cmpxchg(xa, index, NULL, entry, gfp);
+	if (!curr)
+		return 0;
+	if (xa_is_err(curr))
+		return xa_err(curr);
+	return -EEXIST;
+}
+
+/**
  * xa_erase_bh() - Erase this entry from the XArray.
  * @xa: XArray.
  * @index: Index of entry.