[PATCH 21/26] xor: add a better public API

Christoph Hellwig
2026-03-24T06:27:02Z

xor_blocks is very annoying to use, because it is limited to 4 + 1
sources / destinations, has an odd argument order and is completely
undocumented.

Lift the code that loops around it from btrfs and async_tx/async_xor into
common code under the name xor_gen and properly document it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
include/linux/raid/xor.h | 2 ++
lib/raid/xor/xor-core.c | 32 ++++++++++++++++++++++++++++++++
2 files changed, 34 insertions(+)

diff --git a/include/linux/raid/xor.h b/include/linux/raid/xor.h
index 02bda8d99534..6d9a39fd85dd 100644
--- a/include/linux/raid/xor.h
+++ b/include/linux/raid/xor.h
@@ -7,4 +7,6 @@
extern void xor_blocks(unsigned int count, unsigned int bytes,
void *dest, void **srcs);

+void xor_gen(void *dest, void **srcs, unsigned int src_cnt, unsigned int bytes);
+
#endif /* _XOR_H */
diff --git a/lib/raid/xor/xor-core.c b/lib/raid/xor/xor-core.c
index 47e09ae954b2..fdd0cf5584e7 100644
--- a/lib/raid/xor/xor-core.c
+++ b/lib/raid/xor/xor-core.c
@@ -46,6 +46,38 @@ xor_blocks(unsigned int src_count, unsigned int bytes, void *dest, void **srcs)
}
EXPORT_SYMBOL(xor_blocks);

+/**
+ * xor_gen - generate RAID-style XOR information
+ * @dest: destination vector
+ * @srcs: source vectors
+ * @src_cnt: number of source vectors
+ * @bytes: length in bytes of each vector
+ *
+ * Performs bit-wise XOR operation into @dest for each of the @src_cnt vectors
+ * in @srcs for a length of @bytes bytes. @src_count must be non-zero, and the
+ * memory pointed to by @dest and each member of @srcs must be at least 64-byte
+ * aligned. @bytes must be non-zero and a multiple of 512.
+ *
+ * Note: for typical RAID uses, @dest either needs to be zeroed, or filled with
+ * the first disk, which then needs to be removed from @srcs.
+ */
+void xor_gen(void *dest, void **srcs, unsigned int src_cnt, unsigned int bytes)
+{
+ unsigned int src_off = 0;
+
+ WARN_ON_ONCE(bytes & 511);
+
+ while (src_cnt > 0) {
+ unsigned int this_cnt = min(src_cnt, MAX_XOR_BLOCKS);
+
+ xor_blocks(this_cnt, bytes, dest, srcs + src_off);
+
+ src_cnt -= this_cnt;
+ src_off += this_cnt;
+ }
+}
+EXPORT_SYMBOL(xor_gen);
+
/* Set of all registered templates. */
static struct xor_block_template *__initdata template_list;
static bool __initdata xor_forced = false;
--
2.47.3