From 6094201431aa981c6e0d149b6d528bc4b7a5af91 Mon Sep 17 00:00:00 2001 From: Qu Wenruo Date: Thu, 16 Jan 2025 19:56:02 +1030 Subject: [PATCH] btrfs-progs: remove loopback device resolution [BUG] mkfs.btrfs has a built-in loopback device resolution, to avoid the same file being added to the same fs, using loopback device and the file itself. But it has one big bug: - It doesn't detect partition on loopback devices correctly The function is_loop_device() only utilize major number to detect a loopback device. But partitions on loopback devices doesn't use the same major number as the loopback device: NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINTS loop0 7:0 0 5G 0 loop |-loop0p1 259:3 0 128M 0 part `-loop0p2 259:4 0 4.9G 0 part Thus `/dev/loop0p1` will not be treated as a loopback device, thus it will not even resolve the source file. And this can not even be fixed, as if we do extra "/dev/loop*" based file lookup, `/dev/loop0p1` and `/dev/loop0p2` will resolve to the same source file, and refuse to mkfs on two different partitions. [FIX] The loopback file detection is the baby sitting that no one asks for. Just as I explained, it only brings new bugs, and we will never fix all ways that an experienced user can come up with. And I didn't see any other mkfs tool doing such baby sitting. So remove the loopback file resolution, just regular is_same_blk_file() is good enough. Signed-off-by: Qu Wenruo --- common/open-utils.c | 7 ++- common/path-utils.c | 127 +------------------------------------------- common/path-utils.h | 2 +- 3 files changed, 5 insertions(+), 131 deletions(-) diff --git a/common/open-utils.c b/common/open-utils.c index 8490be4af0..a292177691 100644 --- a/common/open-utils.c +++ b/common/open-utils.c @@ -36,8 +36,7 @@ #include "common/open-utils.h" /* - * Check if a file is used (directly or indirectly via a loop device) by a - * device in fs_devices + * Check if a file is used by a device in fs_devices */ static int blk_file_in_dev_list(struct btrfs_fs_devices* fs_devices, const char* file) @@ -46,7 +45,7 @@ static int blk_file_in_dev_list(struct btrfs_fs_devices* fs_devices, struct btrfs_device *device; list_for_each_entry(device, &fs_devices->devices, dev_list) { - if((ret = is_same_loop_file(device->name, file))) + if((ret = is_same_blk_file(device->name, file))) return ret; } @@ -94,7 +93,7 @@ int check_mounted_where(int fd, const char *file, char *where, int size, else if(!ret) continue; - ret = is_same_loop_file(file, mnt->mnt_fsname); + ret = is_same_blk_file(file, mnt->mnt_fsname); } if(ret < 0) diff --git a/common/path-utils.c b/common/path-utils.c index 04861d1668..3030ddc47f 100644 --- a/common/path-utils.c +++ b/common/path-utils.c @@ -107,87 +107,11 @@ int path_exists(const char *path) return 1; } -/* checks if a device is a loop device */ -static int is_loop_device(const char *device) -{ - struct stat statbuf; - - if(stat(device, &statbuf) < 0) - return -errno; - - return (S_ISBLK(statbuf.st_mode) && - MAJOR(statbuf.st_rdev) == LOOP_MAJOR); -} - -/* - * Takes a loop device path (e.g. /dev/loop0) and returns - * the associated file (e.g. /images/my_btrfs.img) using - * loopdev API - */ -static int resolve_loop_device_with_loopdev(const char* loop_dev, char* loop_file) -{ - int fd; - int ret; - struct loop_info64 lo64; - - fd = open(loop_dev, O_RDONLY | O_NONBLOCK); - if (fd < 0) - return -errno; - ret = ioctl(fd, LOOP_GET_STATUS64, &lo64); - if (ret < 0) { - ret = -errno; - goto out; - } - - memcpy(loop_file, lo64.lo_file_name, sizeof(lo64.lo_file_name)); - loop_file[sizeof(lo64.lo_file_name)] = 0; - -out: - close(fd); - - return ret; -} - -/* - * Takes a loop device path (e.g. /dev/loop0) and returns - * the associated file (e.g. /images/my_btrfs.img) - */ -static int resolve_loop_device(const char* loop_dev, char* loop_file, - int max_len) -{ - int ret; - FILE *f; - char fmt[20]; - char p[PATH_MAX]; - char real_loop_dev[PATH_MAX]; - - if (!realpath(loop_dev, real_loop_dev)) - return -errno; - snprintf(p, PATH_MAX, "/sys/block/%s/loop/backing_file", strrchr(real_loop_dev, '/')); - if (!(f = fopen(p, "r"))) { - if (errno == ENOENT) - /* - * It's possibly a partitioned loop device, which is - * resolvable with loopdev API. - */ - return resolve_loop_device_with_loopdev(loop_dev, loop_file); - return -errno; - } - - snprintf(fmt, 20, "%%%i[^\n]", max_len - 1); - ret = fscanf(f, fmt, loop_file); - fclose(f); - if (ret == EOF) - return -errno; - - return 0; -} - /* * Checks whether a and b are identical or device * files associated with the same block device */ -static int is_same_blk_file(const char* a, const char* b) +int is_same_blk_file(const char* a, const char* b) { struct stat st_buf_a, st_buf_b; char real_a[PATH_MAX]; @@ -224,55 +148,6 @@ static int is_same_blk_file(const char* a, const char* b) return 0; } -/* - * Checks if a and b are identical or device files associated with the same - * block device or if one file is a loop device that uses the other file. - */ -int is_same_loop_file(const char *a, const char *b) -{ - char res_a[PATH_MAX]; - char res_b[PATH_MAX]; - const char* final_a = NULL; - const char* final_b = NULL; - int ret; - - /* Resolve a if it is a loop device */ - if ((ret = is_loop_device(a)) < 0) { - if (ret == -ENOENT) - return 0; - return ret; - } else if (ret) { - ret = resolve_loop_device(a, res_a, sizeof(res_a)); - if (ret < 0) { - if (errno != EPERM) - return ret; - } else { - final_a = res_a; - } - } else { - final_a = a; - } - - /* Resolve b if it is a loop device */ - if ((ret = is_loop_device(b)) < 0) { - if (ret == -ENOENT) - return 0; - return ret; - } else if (ret) { - ret = resolve_loop_device(b, res_b, sizeof(res_b)); - if (ret < 0) { - if (errno != EPERM) - return ret; - } else { - final_b = res_b; - } - } else { - final_b = b; - } - - return is_same_blk_file(final_a, final_b); -} - /* Checks if a file exists and is a block or regular file*/ int path_is_reg_or_block_device(const char *filename) { diff --git a/common/path-utils.h b/common/path-utils.h index 558fa21adf..6efcd81cf8 100644 --- a/common/path-utils.h +++ b/common/path-utils.h @@ -31,7 +31,7 @@ int path_is_a_mount_point(const char *file); int path_exists(const char *file); int path_is_reg_file(const char *path); int path_is_dir(const char *path); -int is_same_loop_file(const char *a, const char *b); +int is_same_blk_file(const char* a, const char* b); int path_is_reg_or_block_device(const char *filename); int path_is_in_dir(const char *parent, const char *path); char *path_basename(char *path);