1 files changed, 86 insertions, 0 deletions
diff --git a/lib/dedupe-range.c b/lib/dedupe-range.c
new file mode 100644
index 0000000..dea70c7
--- /dev/null
+++ b/lib/dedupe-range.c
@@ -0,0 +1,86 @@
+#include <assert.h>    /* for assert(3p) */
+#include <errno.h>     /* for errno */
+#include <error.h>     /* for error(3gnu) */
+#include <fcntl.h>     /* for open(2) */
+#include <inttypes.h>  /* for uint64_t, PRIu64 */
+#include <linux/fs.h>  /* for FIDEDUPRANGE and related */
+#include <stdbool.h>   /* for bool, true, false */
+#include <stdlib.h>    /* for exit(3p), EXIT_SUCCESS, EXIT_FAILURE */
+#include <sys/ioctl.h> /* for ioctl(2) */
+#include <unistd.h>    /* for sysconf(3p), _SC_PAGESIZE */
+
+#include "dedupe-range.h"
+
+#define MIN(a, b) ((a) < (b) ? (a) : (b))
+
+void dedupe_range(struct range src, struct range *dsts) {
+	size_t dst_count;
+	for (dst_count = 0; dsts[dst_count].filename; dst_count++);
+
+	const size_t max_dst_count = (sysconf(_SC_PAGESIZE) - sizeof(struct file_dedupe_range))
+		/ sizeof(struct file_dedupe_range_info);
+
+	int src_fd = open(src.filename, src.flags);
+	if (src_fd < 0)
+		error(EXIT_FAILURE, errno, "open src: %s", src.filename);
+
+	struct file_dedupe_range_info *range_info =
+		calloc(dst_count, sizeof(struct file_dedupe_range_info));
+	for (size_t i = 0; i < dst_count; i++) {
+		int dst_fd = open(dsts[i].filename, dsts[i].flags);
+		if (dst_fd < 0)
+			error(EXIT_FAILURE, errno, "open dst: %s", dsts[i].filename);
+		range_info[i].dest_fd = dst_fd;
+		range_info[i].dest_offset = dsts[i].offset;
+	}
+
+	for (size_t files_deduped = 0; files_deduped < dst_count; ) {
+		uint16_t dest_count = MIN(dst_count - files_deduped, max_dst_count);
+		struct file_dedupe_range *range = malloc(sizeof(struct file_dedupe_range) + dest_count * sizeof(struct file_dedupe_range_info));
+		*range = (struct file_dedupe_range){
+			.src_offset = src.offset,
+			.src_length = src.length,
+			.dest_count = dest_count,
+			.reserved1 = 0,
+			.reserved2 = 0,
+		};
+		for (size_t i = 0; i < dest_count; i++)
+			range->info[i] = range_info[files_deduped+i];
+
+		bool erred = false;
+		while (range->src_length > 0) {
+			if (ioctl(src_fd, FIDEDUPERANGE, &range) < 0)
+				error(EXIT_FAILURE, errno, "ioctl (FIDEDUPERANGE)");
+			uint64_t bytes_deduped = range->info[0].bytes_deduped;
+			assert(bytes_deduped <= range->src_length);
+			for (size_t i = 0; i < range->dest_count; i ++) {
+				if (range->info[i].bytes_deduped != bytes_deduped) {
+					error(0, errno, "dedupe: %"PRIu64" != %"PRIu64": %s",
+					      bytes_deduped,
+					      /* on platforms where both "long" and "long long" 
+					       * are 64 bits, linux __u64 might disagree with 
+					       * glibc uint64_t and thus PRIu64  */
+					      (uint64_t)range->info[i].bytes_deduped,
+					      dsts[files_deduped+i].filename);
+					erred = true;
+				}
+				switch (range->info[i].status) {
+				case FILE_DEDUPE_RANGE_DIFFERS:
+					error(0, 0, "dedupe: range differs: %s", dsts[files_deduped+i].filename);
+					erred = true;
+					break;
+				case FILE_DEDUPE_RANGE_SAME:
+					range->info[i].dest_offset += range->info[i].bytes_deduped;
+					break;
+				default:
+					assert(false);
+				}
+			}
+			if (erred == true)
+				exit(EXIT_FAILURE);
+			range->src_offset += bytes_deduped;
+			range->src_length -= bytes_deduped;
+		}
+		files_deduped += range->dest_count;
+	}
+}