btrfs-progs: mkfs: Separate shrink from rootdir

Make --shrink a separate option for --rootdir, and change the default to
off.

The shrinking behaviour is not a commonly used feature but can be useful
for creating minimal pre-filled images, in one step, without requiring
to mount.

Signed-off-by: Qu Wenruo <wqu@suse.com>
[ update changelog and error messages ]
Signed-off-by: David Sterba <dsterba@suse.com>

Documentation/mkfs.btrfs.asciidoc

@@ -101,6 +101,17 @@ Please see the mount option 'discard' for that in `btrfs`(5).
 *-r|--rootdir <rootdir>*::
 Populate the toplevel subvolume with files from 'rootdir'.  This does not
 require root permissions and does not mount the filesystem.
++
+NOTE: This option may enlarge the image or file to ensure it's large enough to
+contain the files from 'rootdir'.
+
+*--shrink*:
+Shrink the filesystem to its minimal size, only works with *-r|--rootdir*
+option.
++
+NOTE: If the destination is regular file, this option will also reduce the
+file size. Or it will only reduce the filesystem available space.
+Extra space will not be usable unless resized using 'btrfs filesystem resize'.
 
 *-O|--features <feature1>[,<feature2>...]*::
 A list of filesystem features turned on at mkfs time. Not all features are

mkfs/main.c

@@ -731,9 +731,11 @@ int main(int argc, char **argv)
 	int ssd = 0;
 	int force_overwrite = 0;
 	char *source_dir = NULL;
-	int source_dir_set = 0;
+	bool source_dir_set = false;
+	bool shrink_rootdir = false;
 	u64 source_dir_size = 0;
 	u64 min_dev_size;
+	u64 shrink_size;
 	int dev_cnt = 0;
 	int saved_optind;
 	char fs_uuid[BTRFS_UUID_UNPARSED_SIZE] = { 0 };
@@ -743,6 +745,7 @@ int main(int argc, char **argv)
 
 	while(1) {
 		int c;
+		enum { GETOPT_VAL_SHRINK = 257 };
 		static const struct option long_options[] = {
 			{ "alloc-start", required_argument, NULL, 'A'},
 			{ "byte-count", required_argument, NULL, 'b' },
@@ -760,6 +763,7 @@ int main(int argc, char **argv)
 			{ "features", required_argument, NULL, 'O' },
 			{ "uuid", required_argument, NULL, 'U' },
 			{ "quiet", 0, NULL, 'q' },
+			{ "shrink", no_argument, NULL, GETOPT_VAL_SHRINK },
 			{ "help", no_argument, NULL, GETOPT_VAL_HELP },
 			{ NULL, 0, NULL, 0}
 		};
@@ -827,7 +831,7 @@ int main(int argc, char **argv)
 				goto success;
 			case 'r':
 				source_dir = optarg;
-				source_dir_set = 1;
+				source_dir_set = true;
 				break;
 			case 'U':
 				strncpy(fs_uuid, optarg,
@@ -839,6 +843,9 @@ int main(int argc, char **argv)
 			case 'q':
 				verbose = 0;
 				break;
+			case GETOPT_VAL_SHRINK:
+				shrink_rootdir = true;
+				break;
 			case GETOPT_VAL_HELP:
 			default:
 				print_usage(c != GETOPT_VAL_HELP);
@@ -861,6 +868,10 @@ int main(int argc, char **argv)
 		error("the option -r is limited to a single device");
 		goto error;
 	}
+	if (shrink_rootdir && !source_dir_set) {
+		error("the option --shrink must be used with --rootdir");
+		goto error;
+	}
 
 	if (*fs_uuid) {
 		uuid_t dummy_uuid;
@@ -1189,10 +1200,14 @@ raid_groups:
 			error("error wihle filling filesystem: %d", ret);
 			goto out;
 		}
-		ret = btrfs_mkfs_shrink_fs(fs_info, NULL);
-		if (ret < 0) {
-			error("error while shrinking filesystem: %d", ret);
-			goto out;
+		if (shrink_rootdir) {
+			ret = btrfs_mkfs_shrink_fs(fs_info, &shrink_size,
+						   shrink_rootdir);
+			if (ret < 0) {
+				error("error while shrinking filesystem: %d",
+					ret);
+				goto out;
+			}
 		}
 	}
 

mkfs/rootdir.c

@@ -899,11 +899,13 @@ err:
 	return ret;
 }
 
-int btrfs_mkfs_shrink_fs(struct btrfs_fs_info *fs_info, u64 *new_size_ret)
+int btrfs_mkfs_shrink_fs(struct btrfs_fs_info *fs_info, u64 *new_size_ret,
+			 bool shrink_file_size)
 {
 	u64 new_size;
 	struct btrfs_device *device;
 	struct list_head *cur;
+	struct stat64 file_stat;
 	int nr_devs = 0;
 	int ret;
 
@@ -931,5 +933,22 @@ int btrfs_mkfs_shrink_fs(struct btrfs_fs_info *fs_info, u64 *new_size_ret)
 		return ret;
 	if (new_size_ret)
 		*new_size_ret = new_size;
+
+	if (shrink_file_size) {
+		ret = fstat64(device->fd, &file_stat);
+		if (ret < 0) {
+			error("failed to stat devid %llu: %s", device->devid,
+				strerror(errno));
+			return ret;
+		}
+		if (!S_ISREG(file_stat.st_mode))
+			return ret;
+		ret = ftruncate64(device->fd, new_size);
+		if (ret < 0) {
+			error("failed to truncate device file of devid %llu: %s",
+				device->devid, strerror(errno));
+			return ret;
+		}
+	}
 	return ret;
 }

mkfs/rootdir.h

@@ -32,6 +32,7 @@ int btrfs_mkfs_fill_dir(const char *source_dir, struct btrfs_root *root,
 			bool verbose);
 u64 btrfs_mkfs_size_dir(const char *dir_name, u32 sectorsize, u64 min_dev_size,
 			u64 meta_profile, u64 data_profile);
-int btrfs_mkfs_shrink_fs(struct btrfs_fs_info *fs_info, u64 *new_size_ret);
+int btrfs_mkfs_shrink_fs(struct btrfs_fs_info *fs_info, u64 *new_size_ret,
+			 bool shrink_file_size);
 
 #endif