https://github.com/0x2b3bfa0/qdtar

Documentation for the file format used to upgrade the Qisda-ES600 e-reader.
https://github.com/0x2b3bfa0/qdtar

bq-avant bq-avant3 e-reader es600 qdtar qisda s3c2416 tar

Last synced: 3 months ago
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Documentation for the file format used to upgrade the Qisda-ES600 e-reader.

• Host: GitHub
• URL: https://github.com/0x2b3bfa0/qdtar
• Owner: 0x2b3bfa0
• License: gpl-2.0
• Created: 2017-08-15T20:40:46.000Z (almost 8 years ago)
• Default Branch: master
• Last Pushed: 2021-09-25T20:58:12.000Z (over 3 years ago)
• Last Synced: 2024-10-04T13:21:52.962Z (9 months ago)
• Topics: bq-avant, bq-avant3, e-reader, es600, qdtar, qisda, s3c2416, tar
• Language: Shell
• Homepage:
• Size: 39.1 KB
• Stars: 0
• Watchers: 2
• Forks: 1
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

        
# qdtar

A `qdtar` archive is a slightly modified `tar` archive, used to pack the root filesystem in the Qisda ES600 e-reader upgrades. The file name used for these archives is `rootfs.img`, even if it has nothing to do with a disk image.

***

This kind of file is formed by a header of 978 bytes, whose contents are completely ignored, prepended to a normal `tar` archive. 

The [executable found on the firmware](busybox) zero-fills the header when creating a new archive. However, the archives found in official firmware upgrade packages used a different approach:

* The first 970 bytes of the header were filled with a copy of the first 970 bytes of the `tar` file.

* The next 8 bytes were used to store the magic number (`QDTAR1.0`).

I suspect that filling of the header with a copy of the first bytes of the `tar` file was only a mistake made by the developer of the packer application. Probably the original code shifts the data on a buffer by copying it to the new offset without taking care of zeroing the contents of the header. There is, however, anoher credible explanation: copying the first bytes of the `tar` archive will fool a normal decompression utility.