first pass at cow-extent-map

4 files changed, 143 insertions, 1 deletions

diff --git a/Makefile b/Makefile
index e6dffd6..6cf34d9 100644
--- a/Makefile
+++ b/Makefile
@@ -5,10 +5,14 @@ CFLAGS += -Wall -Werror -Wextra
 CPPFLAGS += -O2 -D_FORTIFY_SOURCE=2
 
 all: cow-dedupe-range
+all: cow-extent-map
 .PHONY: all
 
-cow-dedupe-range: src/cow-dedupe-range.o lib/dedupe-range.o
+%: src/%.o
 	$(CC) $(LDFLAGS) -o $@ $^
 
+cow-dedupe-range: lib/dedupe-range.o
+cow-extent-map: lib/extent-map.o
+
 .SECONDARY:
 .DELETE_ON_ERROR:
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));
diff --git a/src/cow-extent-map.c b/src/cow-extent-map.c
new file mode 100644
index 0000000..7cee70c
--- /dev/null
+++ b/src/cow-extent-map.c
@@ -0,0 +1,93 @@
+#define _GNU_SOURCE   /* for program_invocation_name */
+#include <assert.h>   /* for assert(3p) */
+#include <errno.h>    /* for errno, program_invocation_name */
+#include <error.h>    /* for error(3gnu) */
+#include <fcntl.h>    /* for open(2) and O_RDONLY */
+#include <getopt.h>   /* for getopt_long(3gnu), struct option, optind, optarg */
+#include <inttypes.h> /* PRI* */
+#include <stdio.h>    /* for printf(3p), fprintf(3p), stderr */
+#include <stdlib.h>   /* exit(3p), EXIT_SUCCESS, EXIT_FAILURE */
+#include <string.h>   /* for strcmp(3p) */
+
+#include "extent-map.h" /* for uint32_t, fiemap stuff */ 
+
+#define EXIT_INVALIDARGUMENT 2
+#define errusage(format, ...) do { \
+	error(0, 0, format, ## __VA_ARGS__); \
+	fprintf(stderr, "Try '%s --help' for more information.\n", program_invocation_name); \
+	exit(EXIT_INVALIDARGUMENT); \
+} while(0)
+
+int print_extent(struct fiemap_extent extent) {
+	printf("logical=%"PRIu64" "
+	       "physical=%"PRIu64" "
+	       "length=%"PRIu64" "
+	       "flags=0x%"PRIx32"\n",
+	       extent.fe_logical,
+	       extent.fe_physical,
+	       extent.fe_length,
+	       extent.fe_flags);
+	return 0;
+}
+
+void usage() {
+	printf("Usage: %s [OPTIONS] FILENAME\n"
+	       "Print a file extent map.\n"
+	       "\n"
+	       "OPTIONS:\n"
+	       "  --stream=data   Map extents in the data stream (default).\n"
+	       "  --stream=xattr  Map extents in the extended attribute stream.\n"
+	       "  --sync          Sync the file before mapping extents (default).\n"
+	       "  --no-sync       Don't sync the file before mapping extents.\n"
+	       "  -h, --help      Display this help and exit.\n",
+	       program_invocation_name);
+}
+
+int main(int argc, char *argv[]) {
+	char *stream = "data";
+	int sync = 1;
+	struct option long_options[] = {
+		{"stream",  optional_argument, NULL, 1},
+		{"sync",    no_argument,       &sync, 1},
+		{"no-sync", no_argument,       &sync, 0},
+		{"help",    no_argument,       NULL, 'h'},
+		{0},
+	};
+	int flag;
+	while ((flag = getopt_long(argc, argv, "h", long_options, NULL)) >= 0) {
+		switch (flag) {
+		case 0:
+			break;
+		case 1:
+			stream = optarg;
+			break;
+		case 'h':
+			usage();
+			return EXIT_SUCCESS;
+		case '?':
+			fprintf(stderr, "Try '%s --help' for more information.\n", program_invocation_name);
+			return EXIT_INVALIDARGUMENT;
+		default:
+			assert(0);
+		}
+	}
+	if (argc - optind != 1)
+		errusage("wrong number of arguments");
+
+	uint32_t flags = sync ? FIEMAP_FLAG_SYNC : 0;
+	if (strcmp(stream, "data") == 0) {
+		/* do nothing */
+	} else if (strcmp(stream, "xattr") == 0) {
+		flags |= FIEMAP_FLAG_XATTR;
+	} else {
+		errusage("invalid stream name");
+	}
+
+	char *filename = argv[optind];
+	int fd = open(filename, O_RDONLY);
+	if (fd < 0)
+		error(EXIT_FAILURE, errno, "%s", filename);
+
+	fiemap(fd, flags, print_extent);
+	return EXIT_SUCCESS;;
+}