first pass at cow-extent-map

2 files changed, 45 insertions, 0 deletions

diff --git a/lib/extent-map.c b/lib/extent-map.c
new file mode 100644
index 0000000..b698fa1
--- /dev/null
+++ b/lib/extent-map.c
@@ -0,0 +1,41 @@
+#include <errno.h>        /* for errno */
+#include <error.h>        /* for error(3gnu) */
+#include <linux/fiemap.h> /* for all of the other fiemap stuff */
+#include <linux/fs.h>     /* for FS_IOC_FIEMAP */
+#include <stdlib.h>       /* for calloc(3p), exit(3p), EXIT_SUCCESS, EXIT_FAILURE */
+#include <sys/ioctl.h>    /* for ioctl(2) */
+#include <unistd.h>       /* for sysconf(3p), _SC_PAGESIZE */
+
+#include "extent-map.h"
+
+void fiemap(int fd, uint32_t flags, int (*handle_extent)(struct fiemap_extent)) {
+		const size_t fm_size = sysconf(_SC_PAGESIZE);;
+	struct fiemap *fm = calloc(1, fm_size);
+	if (!fm)
+		error(EXIT_FAILURE, errno, "malloc");
+	uint64_t bytes_mapped = 0;
+	while (1) {
+		*fm = (struct fiemap){
+			.fm_start = bytes_mapped,
+			.fm_length = FIEMAP_MAX_OFFSET - bytes_mapped,
+			.fm_flags = flags,
+			.fm_extent_count = (fm_size - sizeof(struct fiemap)) / sizeof(struct fiemap_extent),
+		};
+
+		if (ioctl(fd, FS_IOC_FIEMAP, fm) < 0)
+			error(EXIT_FAILURE, errno, "ioctl (FS_IOC_FIEMAP)");
+
+		for (size_t i = 0; i < fm->fm_extent_count; i++) {
+			int r = handle_extent(fm->fm_extents[i]);
+			if (r) {
+				free(fm);
+				exit(r);
+			}
+
+			if (fm->fm_extents[i].fe_flags & FIEMAP_EXTENT_LAST) {
+				free(fm);
+				exit(EXIT_SUCCESS);
+			}
+		}
+	}		
+}
diff --git a/lib/extent-map.h b/lib/extent-map.h
new file mode 100644
index 0000000..4f873a0
--- /dev/null
+++ b/lib/extent-map.h
@@ -0,0 +1,4 @@
+#include <stdint.h>       /* for uint32_t */
+#include <linux/fiemap.h> /* for struct fiemap_extent */
+
+void fiemap(int fd, uint32_t flags, int (*handle_extent)(struct fiemap_extent));