Why does android download system image in every project

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Platform Architecture Generic System Image. Support library. Revision History. Android Developers. The bootloader then appends the command line specified in the boot image to the end of the bootloader-generated command line.

These images use a standard Linux format such as zImage , Image , or Image. When creating kernel images, concatenated device-tree binaries are recommended instead of a separate partition for the device tree.

When using multiple device tree blobs DTBs for different board revisions, concatenate multiple DTBs in descending order of board revision. These images contain a root file system suitable for mounting as a rootfs. They are combined with kernel images using mkbootfs then flashed into the boot partition. File system. These images include system , userdata , and recovery images and must use Yaffs2 format or sparse image format.

The bootloader is responsible for consuming these images and relocating the yaffs extra data into the appropriate location in the out-of-band area for the given NAND hardware. If software ECC is required, the bootloader should also do that computation at this time.

For details on the image format, refer to the Yaffs 2 Specification. Devices using block-based storage should support ext4 or f2fs. To quickly transfer and flash large, empty ext4 file systems such as userdata , store the image in a sparse format that contains information about which areas of the file system can be left unwritten.

The sparse image format contains a file header, followed by a series of chunks. The file header, chunk header, and chunk data are multiples of 4 bytes, and all fields are unsigned little-endian. You can use the mke2fs utility to create images in sparse image format this is also the tool used to create the images the bootloader reads and flashes.

The mke2fs utility knows what areas of the image need to be written and encodes "don't care" chunks between them. Another tool, img2simg , converts non-sparse images to sparse images. Regular images have no information about "don't care" areas; the best a conversion can do is look for blocks of repeated data to reduce the resulting image size. Readers should reject images with unknown major versions but accept images with unknown minor versions.

Readers might reject images with chunk sizes they don't support. Ater the major version is validated, the reader should ignore chunks with unknown type fields, skipping over the chunk in the file using the "chunk size in file" and skipping "chunk size in blocks" blocks on the output.

A cyclic redundancy check Any area that isn't written don't care, or a skipped chunk , should be counted as 0s in the CRC. The total number of blocks written or skipped should be compared against the "total blocks" field in the header. The tool simg2img converts the sparse image format to a standard image, which loses the sparse information. The flash command shouldn't erase the partition unless the host fastboot tool sends an erase command first.

This allows flashing a very large partition in multiple smaller chunks using multiple sparse images that start with a "skip" block to seek over the already-written area. Creating these images on demand is already handled by the fastboot host side tool.

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