[PATCH] fstools: add support of mapped rootfs

[paul.henrys_ext at softathome.com]

From: Paul HENRYS <paul.henrys_ext at softathome.com>

When the rootfs is signed and/or ciphered and dmsetup is used, virtual
block devices are created and mapped to the physical block device where
the rootfs is actually stored.
Inside mount_root.c, when volume_find("rootfs_data") is called in start(),
the implementation iterates over the registered drivers and eventually
when the rootfs is mapped, when calling rootdisk_volume_find(), the
virtual device is pointed by rootdev instead of the physical device which
should be used.

Hereafter is an example of mapped rootfs (signed and ciphered) stored in a
UBI device:

   / # dmsetup ls --tree
   vrootfs_crypt (253:1)
    `-vrootfs_linear (253:0)
       `- (254:0)
   / # cat /sys/class/block/dm-1/dev
   253:1
   / # cat /sys/class/block/dm-0/dev
   253:0
   / # cat /sys/class/block/ubiblock0_5/dev
   254:0
   / # cat /sys/class/ubi/ubi0_5/name
   rootfs
   / # ls -lrt /sys/class/block/dm-1/slaves/
   lrwxrwxrwx 1 root root 0 Jan  1 00:01 dm-0 -> ../../dm-0
   / # ls -lrt /sys/class/block/dm-1/slaves/dm-0/slaves/
   lrwxrwxrwx 1 root root 0 Jan  1 00:01 ubiblock0_5 -> ../../ubiblock0_5
   / # ls -lrt /sys/class/block/dm-1/slaves/dm-0/slaves/ubiblock0_5/slaves

In such a case, the previous implementation failed to detect the rootfs is
stored in a UBI and did not mount an overlayfs.

The fix looks for slave devices in /sys/class/block to find the physical
block device.

Signed-off-by: Paul HENRYS <paul.henrys_ext at softathome.com>
---
 libfstools/common.c   | 36 ++++++++++++++++++++++++++++++++++++
 libfstools/common.h   | 13 +++++++++++++
 libfstools/rootdisk.c |  8 ++++++++
 3 files changed, 57 insertions(+)

diff --git a/libfstools/common.c b/libfstools/common.c
index e5b7bc3..07cf39d 100644
--- a/libfstools/common.c
+++ b/libfstools/common.c
@@ -176,3 +176,39 @@ do_format:

        return ret;
 }
+
+char *block_get_slave(const char *bdev)
+{
+       int fd = -1;
+       DIR *dirp = NULL;
+       struct dirent *d;
+       char path[256] = {0};
+       static char slave[256];
+       int slaves = 0;
+
+       if (!bdev)
+               goto out;
+
+       snprintf(path, sizeof(path), "/sys/class/block/%s/slaves", bdev);
+       fd = open(path, O_RDONLY|O_CLOEXEC);
+       if (fd < 0)
+               goto out;
+
+       dirp = fdopendir(fd);
+       if (!dirp)
+               goto out;
+
+       while ((d = xreaddir(dirp))) {
+               if (++slaves > 1)
+                       goto out;       /* more than one slave */
+               strncpy(slave, d->d_name, sizeof(slave));
+               slave[sizeof(slave) - 1] = '\0'; /* make sure slave is always NULL terminated */
+       }
+
+ out:
+       if (dirp)
+               closedir(dirp);
+       if  (fd >= 0)
+               close(fd);
+       return slaves == 1 ? slave : NULL;
+}
diff --git a/libfstools/common.h b/libfstools/common.h
index b5cc692..4330ecd 100644
--- a/libfstools/common.h
+++ b/libfstools/common.h
@@ -21,7 +21,20 @@

 #define F2FS_MINSIZE           (100ULL * 1024ULL * 1024ULL)

+/* Look for directories but skip "." and ".." */
+static inline struct dirent *xreaddir(DIR *dirp)
+{
+       struct dirent *d;
+
+       while ((d = readdir(dirp)) &&
+              (!strcmp(d->d_name, ".") || !strcmp(d->d_name, "..")))
+               ;
+
+       return d;
+}
+
 int read_uint_from_file(char *dirname, char *filename, unsigned int *i);
 char *read_string_from_file(const char *dirname, const char *filename, char *buf, size_t bufsz);
 int block_file_identify(FILE *f, uint64_t offset);
 int block_volume_format(struct volume *v, uint64_t offset, const char *bdev);
+char *block_get_slave(const char *bdev);
diff --git a/libfstools/rootdisk.c b/libfstools/rootdisk.c
index 9f2317f..ef6f29e 100644
--- a/libfstools/rootdisk.c
+++ b/libfstools/rootdisk.c
@@ -97,6 +97,8 @@ static struct volume *rootdisk_volume_find(char *name)
 {
        struct squashfs_super_block sb;
        struct rootdev_volume *p;
+       static char slave[256] = {0};
+       char *tmp = NULL;

        if (strcmp(name, "rootfs_data") != 0)
                return NULL;
@@ -108,6 +110,12 @@ static struct volume *rootdisk_volume_find(char *name)
        if (!rootdev)
                return NULL;

+       /* Check for slaves to reach the initial block device */
+       while ((tmp = block_get_slave(basename((char *)rootdev)))) {
+               strncpy(slave, tmp, sizeof(slave));
+               rootdev = slave;
+       }
+
        if (strstr(rootdev, "mtdblock") ||
            strstr(rootdev, "ubiblock"))
                return NULL;
--
2.25.1

-- This message and any attachments herein are confidential, intended solely for the addressees and are SoftAtHome’s ownership. Any unauthorized use or dissemination is prohibited. If you are not the intended addressee of this message, please cancel it immediately and inform the sender.