From 6094201431aa981c6e0d149b6d528bc4b7a5af91 Mon Sep 17 00:00:00 2001
From: Qu Wenruo <wqu@suse.com>
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 <wqu@suse.com>
---
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);