btrfsprogs/btrfs-progs-canonicalize-pathnames-for-device-commands

From: Jeff Mahoney <jeffm@suse.com>
Subject: btrfs-progs: canonicalize pathnames for device commands
References: bnc#880486
Patch-mainline: Submitted to linux-btrfs, 4 Jun 2014

mount(8) will canonicalize pathnames before passing them to the kernel.
Links to e.g. /dev/sda will be resolved to /dev/sda. Links to /dev/dm-#
will be resolved using the name of the device mapper table to
/dev/mapper/<name>.

Btrfs will use whatever name the user passes to it, regardless of whether
it is canonical or not. That means that if a 'btrfs device ready' is
issued on any device node pointing to the original device, it will adopt
the new name instead of the name that was used during mount.

Mounting using /dev/sdb2 will result in df:
/dev/sdb2      209715200 39328 207577088   1% /mnt

# ls -la /dev/whatever-i-like
lrwxrwxrwx 1 root root 4 Jun  4 13:36 /dev/whatever-i-like -> sdb2
# btrfs dev ready /dev/whatever-i-like
# df /mnt
/dev/whatever-i-like 209715200 39328 207577088   1% /mnt

Likewise, mounting with /dev/mapper/whatever and using /dev/dm-0 with a
btrfs device command results in df showing /dev/dm-0. This can happen with
multipath devices with friendly names enabled and doing something like 
'partprobe' which (at least with our version) ends up issuing a 'change'
uevent on the sysfs node. That *always* uses the dm-# name, and we get
confused users.

This patch does the same canonicalization of the paths that mount does
so that we don't end up having inconsistent names reported by ->show_devices
later.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
---
 cmds-device.c  |   60 ++++++++++++++++++++++++++++++++++++++++++++-------------
 cmds-replace.c |   13 ++++++++++--
 utils.c        |   57 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 utils.h        |    2 +
 4 files changed, 117 insertions(+), 15 deletions(-)

--- a/cmds-device.c
+++ b/cmds-device.c
@@ -95,6 +95,7 @@ static int cmd_add_dev(int argc, char **
 		int	devfd, res;
 		u64 dev_block_count = 0;
 		int mixed = 0;
+		char *path;
 
 		res = test_dev_for_mkfs(argv[i], force, estr);
 		if (res) {
@@ -118,15 +119,24 @@ static int cmd_add_dev(int argc, char **
 			goto error_out;
 		}
 
-		strncpy_null(ioctl_args.name, argv[i]);
+		path = canonicalize_path(argv[i]);
+		if (!path) {
+			fprintf(stderr,
+				"ERROR: Could not canonicalize pathname '%s': %s\n",
+				argv[i], strerror(errno));
+			ret++;
+			goto error_out;
+		}
+
+		strncpy_null(ioctl_args.name, path);
 		res = ioctl(fdmnt, BTRFS_IOC_ADD_DEV, &ioctl_args);
 		e = errno;
-		if(res<0){
+		if (res < 0) {
 			fprintf(stderr, "ERROR: error adding the device '%s' - %s\n",
-				argv[i], strerror(e));
+				path, strerror(e));
 			ret++;
 		}
-
+		free(path);
 	}
 
 error_out:
@@ -242,6 +252,7 @@ static int cmd_scan_dev(int argc, char *
 
 	for( i = devstart ; i < argc ; i++ ){
 		struct btrfs_ioctl_vol_args args;
+		char *path;
 
 		if (!is_block_device(argv[i])) {
 			fprintf(stderr,
@@ -249,9 +260,17 @@ static int cmd_scan_dev(int argc, char *
 			ret = 1;
 			goto close_out;
 		}
-		printf("Scanning for Btrfs filesystems in '%s'\n", argv[i]);
+		path = canonicalize_path(argv[i]);
+		if (!path) {
+			fprintf(stderr,
+				"ERROR: Could not canonicalize path '%s': %s\n",
+				argv[i], strerror(errno));
+			ret = 1;
+			goto close_out;
+		}
+		printf("Scanning for Btrfs filesystems in '%s'\n", path);
 
-		strncpy_null(args.name, argv[i]);
+		strncpy_null(args.name, path);
 		/*
 		 * FIXME: which are the error code returned by this ioctl ?
 		 * it seems that is impossible to understand if there no is
@@ -262,9 +281,11 @@ static int cmd_scan_dev(int argc, char *
 
 		if( ret < 0 ){
 			fprintf(stderr, "ERROR: unable to scan the device '%s' - %s\n",
-				argv[i], strerror(e));
+				path, strerror(e));
+			free(path);
 			goto close_out;
 		}
+		free(path);
 	}
 
 close_out:
@@ -284,6 +305,7 @@ static int cmd_ready_dev(int argc, char
 	struct	btrfs_ioctl_vol_args args;
 	int	fd;
 	int	ret;
+	char	*path;
 
 	if (check_argc_min(argc, 2))
 		usage(cmd_ready_dev_usage);
@@ -293,22 +315,34 @@ static int cmd_ready_dev(int argc, char
 		perror("failed to open /dev/btrfs-control");
 		return 1;
 	}
-	if (!is_block_device(argv[1])) {
+
+	path = canonicalize_path(argv[argc - 1]);
+	if (!path) {
 		fprintf(stderr,
-			"ERROR: %s is not a block device\n", argv[1]);
-		close(fd);
-		return 1;
+			"ERROR: Could not canonicalize pathname '%s': %s\n",
+			argv[argc - 1], strerror(errno));
+		ret = 1;
+		goto out;
 	}
 
-	strncpy(args.name, argv[argc - 1], BTRFS_PATH_NAME_MAX);
+	if (!is_block_device(path)) {
+		fprintf(stderr,
+			"ERROR: %s is not a block device\n", path);
+		ret = 1;
+		goto out;
+	}
+
+	strncpy(args.name, path, BTRFS_PATH_NAME_MAX);
 	ret = ioctl(fd, BTRFS_IOC_DEVICES_READY, &args);
 	if (ret < 0) {
 		fprintf(stderr, "ERROR: unable to determine if the device '%s'"
-			" is ready for mounting - %s\n", argv[argc - 1],
+			" is ready for mounting - %s\n", path,
 			strerror(errno));
 		ret = 1;
 	}
 
+out:
+	free(path);
 	close(fd);
 	return ret;
 }
--- a/cmds-replace.c
+++ b/cmds-replace.c
@@ -134,7 +134,7 @@ static int cmd_start_replace(int argc, c
 	int fddstdev = -1;
 	char *path;
 	char *srcdev;
-	char *dstdev;
+	char *dstdev = NULL;
 	int avoid_reading_from_srcdev = 0;
 	int force_using_targetdev = 0;
 	struct stat st;
@@ -204,7 +204,12 @@ static int cmd_start_replace(int argc, c
 	}
 
 	srcdev = argv[optind];
-	dstdev = argv[optind + 1];
+	dstdev = canonicalize_path(argv[optind + 1]);
+	if (!dstdev) {
+		fprintf(stderr,
+			"ERROR: Could not canonicalize path '%s': %s\n",
+			argv[optind + 1], strerror(errno));
+	}
 
 	if (is_numerical(srcdev)) {
 		struct btrfs_ioctl_fs_info_args fi_args;
@@ -278,6 +283,8 @@ static int cmd_start_replace(int argc, c
 
 	close(fddstdev);
 	fddstdev = -1;
+	free(dstdev);
+	dstdev = NULL;
 
 	dev_replace_handle_sigint(fdmnt);
 	if (!do_not_background) {
@@ -312,6 +319,8 @@ static int cmd_start_replace(int argc, c
 	return 0;
 
 leave_with_error:
+	if (dstdev)
+		free(dstdev);
 	if (fdmnt != -1)
 		close(fdmnt);
 	if (fdsrcdev != -1)
--- a/utils.c
+++ b/utils.c
@@ -987,6 +987,63 @@ static int blk_file_in_dev_list(struct b
 }
 
 /*
+ * Resolve a pathname to a device mapper node to /dev/mapper/<name>
+ * Returns NULL on invalid input or malloc failure; Other failures
+ * will be handled by the caller using the input pathame.
+ */
+char *canonicalize_dm_name(const char *ptname)
+{
+	FILE	*f;
+	size_t	sz;
+	char	path[256], name[256], *res = NULL;
+
+	if (!ptname || !*ptname)
+		return NULL;
+
+	snprintf(path, sizeof(path), "/sys/block/%s/dm/name", ptname);
+	if (!(f = fopen(path, "r")))
+		return NULL;
+
+	/* read <name>\n from sysfs */
+	if (fgets(name, sizeof(name), f) && (sz = strlen(name)) > 1) {
+		name[sz - 1] = '\0';
+		snprintf(path, sizeof(path), "/dev/mapper/%s", name);
+
+		if (access(path, F_OK) == 0)
+			res = strdup(path);
+	}
+	fclose(f);
+	return res;
+}
+
+/*
+ * Resolve a pathname to a canonical device node, e.g. /dev/sda1 or
+ * to a device mapper pathname.
+ * Returns NULL on invalid input or malloc failure; Other failures
+ * will be handled by the caller using the input pathame.
+ */
+char *canonicalize_path(const char *path)
+{
+	char *canonical, *p;
+
+	if (!path || !*path)
+		return NULL;
+
+	canonical = realpath(path, NULL);
+	if (!canonical)
+		return strdup(path);
+	p = strrchr(canonical, '/');
+	if (p && strncmp(p, "/dm-", 4) == 0 && isdigit(*(p + 4))) {
+		char *dm = canonicalize_dm_name(p + 1);
+		if (dm) {
+			free(canonical);
+			return dm;
+		}
+	}
+	return canonical;
+}
+
+/*
  * returns 1 if the device was mounted, < 0 on error or 0 if everything
  * is safe to continue.
  */
--- a/utils.h
+++ b/utils.h
@@ -61,6 +61,8 @@ int btrfs_add_to_fsid(struct btrfs_trans
 int btrfs_scan_for_fsid(int run_ioctls);
 void btrfs_register_one_device(char *fname);
 int btrfs_scan_one_dir(char *dirname, int run_ioctl);
+char *canonicalize_dm_name(const char *ptname);
+char *canonicalize_path(const char *path);
 int check_mounted(const char *devicename);
 int check_mounted_where(int fd, const char *file, char *where, int size,
 			struct btrfs_fs_devices **fs_devices_mnt);