aboot: Add support for "compressed ext4" sparse images
Compressed ext4 file system sparse image format is defined by
AOSP and generation of these images is done using ext4_utils
which is also part of Android Open Source Project.
In order to transfer and flash large, empty ext4 filesystems
(userdata) in a reasonable amount of time, we need to store
the image in a sparse format that contains information about
which areas of the filesystem can be left unwritten.
Compressed ext4 file format:
All fields are unsigned little-endian File contains a file header,
followed by a series of chunks File header, chunk header, and chunk
data are all multiples of 4 bytes long
Header:
32 bit magic: 0xed26ff3a
16 bit major version (0x1) - reject images with higher major versions
16 bit minor version (0x0) - allow images with higher minor versions
16 bit file header size in bytes (28 in v1.0)
16 bit chunk header size in bytes (12 in v1.0)
32 bit block size in bytes, must be multiple of 4
32 bit total blocks in output file
32 bit total chunks in input file
Chunk:
16 bit chunk type:
0xCAC1 raw
0xCAC2 fill
0xCAC3 don't care
0xCAC4 crc
16 bits reserved (write as 0, ignore on read)
32 bit chunk size in blocks in output image
32 bit total size in bytes of chunk input file including chunk header and data
Data:
for raw, raw data, size in blocks * block size in bytes
for fill, 4 bytes of fill data
Change-Id: I5ee5c288dae9a8ae364502ae8f32fcab65d2274b
2 files changed