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.
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| @@ -975,6 +975,77 @@ void *__xa_store(struct xarray *xa, unsigned long index, void *entry, gfp_t gfp) · 974 unmodified lines | ||
| 975 | 975 | } |
| 976 | 976 | EXPORT_SYMBOL(__xa_store); |
| 977 | 977 | |
| 978 | +/** | |
| 979 | + * xa_cmpxchg() - Conditionally replace an entry in the XArray. | |
| 980 | + * @xa: XArray. | |
| 981 | + * @index: Index into array. | |
| 982 | + * @old: Old value to test against. | |
| 983 | + * @entry: New value to place in array. | |
| 984 | + * @gfp: Memory allocation flags. | |
| 985 | + * | |
| 986 | + * If the entry at @index is the same as @old, replace it with @entry. | |
| 987 | + * If the return value is equal to @old, then the exchange was successful. | |
| 988 | + * | |
| 989 | + * Context: Process context. Takes and releases the xa_lock. May sleep | |
| 990 | + * if the @gfp flags permit. | |
| 991 | + * Return: The old value at this index or xa_err() if an error happened. | |
| 992 | + */ | |
| 993 | +void *xa_cmpxchg(struct xarray *xa, unsigned long index, | |
| 994 | + void *old, void *entry, gfp_t gfp) | |
| 995 | +{ | |
| 996 | + XA_STATE(xas, xa, index); | |
| 997 | + void *curr; | |
| 998 | + | |
| 999 | + if (WARN_ON_ONCE(xa_is_internal(entry))) | |
| 1000 | + return XA_ERROR(-EINVAL); | |
| 1001 | + | |
| 1002 | + do { | |
| 1003 | + xas_lock(&xas); | |
| 1004 | + curr = xas_load(&xas); | |
| 1005 | + if (curr == old) | |
| 1006 | + xas_store(&xas, entry); | |
| 1007 | + xas_unlock(&xas); | |
| 1008 | + } while (xas_nomem(&xas, gfp)); | |
| 1009 | + | |
| 1010 | + return xas_result(&xas, curr); | |
| 1011 | +} | |
| 1012 | +EXPORT_SYMBOL(xa_cmpxchg); | |
| 1013 | + | |
| 1014 | +/** | |
| 1015 | + * __xa_cmpxchg() - Store this entry in the XArray. | |
| 1016 | + * @xa: XArray. | |
| 1017 | + * @index: Index into array. | |
| 1018 | + * @old: Old value to test against. | |
| 1019 | + * @entry: New entry. | |
| 1020 | + * @gfp: Memory allocation flags. | |
| 1021 | + * | |
| 1022 | + * You must already be holding the xa_lock when calling this function. | |
| 1023 | + * It will drop the lock if needed to allocate memory, and then reacquire | |
| 1024 | + * it afterwards. | |
| 1025 | + * | |
| 1026 | + * Context: Any context. Expects xa_lock to be held on entry. May | |
| 1027 | + * release and reacquire xa_lock if @gfp flags permit. | |
| 1028 | + * Return: The old entry at this index or xa_err() if an error happened. | |
| 1029 | + */ | |
| 1030 | +void *__xa_cmpxchg(struct xarray *xa, unsigned long index, | |
| 1031 | + void *old, void *entry, gfp_t gfp) | |
| 1032 | +{ | |
| 1033 | + XA_STATE(xas, xa, index); | |
| 1034 | + void *curr; | |
| 1035 | + | |
| 1036 | + if (WARN_ON_ONCE(xa_is_internal(entry))) | |
| 1037 | + return XA_ERROR(-EINVAL); | |
| 1038 | + | |
| 1039 | + do { | |
| 1040 | + curr = xas_load(&xas); | |
| 1041 | + if (curr == old) | |
| 1042 | + xas_store(&xas, entry); | |
| 1043 | + } while (__xas_nomem(&xas, gfp)); | |
| 1044 | + | |
| 1045 | + return xas_result(&xas, curr); | |
| 1046 | +} | |
| 1047 | +EXPORT_SYMBOL(__xa_cmpxchg); | |
| 1048 | + | |
| 978 | 1049 | /** |
| 979 | 1050 | * __xa_set_mark() - Set this mark on this entry while locked. |
| 980 | 1051 | * @xa: XArray. |