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https://source.android.com/docs/core/ota/dynamic_partitions/implement

The supported dynamic partitions are:
System
Vendor Product
System Ext
ODM
Note: Avoid placing userdata or any other permanent read-write partition inside super.

According to the source.android.com documentation, userdata is not dynamically partitioned?

version: Android 10

s:/ $ ls -l /dev/block/mapper/
total 0
lrwxrwxrwx 1 root root 15 1970-04-02 04:41 odm -> /dev/block/dm-3
lrwxrwxrwx 1 root root 15 1970-04-02 04:41 odm-verity -> /dev/block/dm-7
lrwxrwxrwx 1 root root 15 1970-04-02 04:41 product -> /dev/block/dm-1
lrwxrwxrwx 1 root root 15 1970-04-02 04:41 product-verity -> /dev/block/dm-5
lrwxrwxrwx 1 root root 15 1970-04-02 04:41 system -> /dev/block/dm-0
lrwxrwxrwx 1 root root 15 1970-04-02 04:41 system-verity -> /dev/block/dm-4
lrwxrwxrwx 1 root root 15 1970-04-02 04:41 userdata -> /dev/block/dm-8
lrwxrwxrwx 1 root root 15 1970-04-02 04:41 vendor -> /dev/block/dm-2
lrwxrwxrwx 1 root root 15 1970-04-02 04:41 vendor-verity -> /dev/block/dm-6

s:/ $ df -h
Filesystem       Size  Used Avail Use% Mounted on
/dev/block/dm-4  3.8G  3.8G     0 100% /
tmpfs            3.7G  1.1M  3.7G   1% /dev
tmpfs            3.7G     0  3.7G   0% /mnt
tmpfs            3.7G     0  3.7G   0% /apex
/dev/block/dm-5  450M  449M     0 100% /product
/dev/block/dm-6  2.3G  2.3G     0 100% /vendor
/dev/block/dm-7  118M  900K  115M   1% /odm
none             3.7G     0  3.7G   0% /sys/fs/cgroup
/dev/block/sda29 356M  3.3M  341M   1% /cache
/dev/block/sda13 4.9M  160K  4.8M   4% /dev/logfs
/dev/block/sda31 976M  862M   87M  91% /cust
/dev/block/dm-8  226G  100G  126G  45% /data
...
hrdom
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1 Answers1

0

Roughly speaking, /dev/block/mapper/userdata partition is by the /dev/block/by name/userdata partition map. Through an encryption or decryption mechanism. It should encrypt or decrypt the original userdata partition using the key in the metadata partition to get a partition like dm-x.
I haven't looked too closely into the details.

Note that we make an exception for metadata-encrypted devices, since dm-default-key is already a wrapper.

https://cs.android.com/android/platform/superproject/+/master:system/core/fs_mgr/fs_mgr.cpp

static bool create_crypto_blk_dev(const std::string& dm_name, uint64_t nr_sec,
                                  const std::string& target_type, const KeyBuffer& crypt_params,
                                  std::string* crypto_blkdev)
bool fscrypt_mount_metadata_encrypted(const std::string& blk_device, const std::string& mount_point,
                                  bool needs_encrypt) {

https://cs.android.com/android/platform/superproject/+/master:system/vold/MetadataCrypt.cpp

hrdom
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