Transparent Decompression Support For EXT4

A Mozilla engineer has been developing transparent decompression support for the EXT4 file-system to benefit Firefox on Android, among other use-cases.

Firefox for Android right now has its libxul.so component compressed and loaded into memory via a custom linker. However, to avoid having to use a custom linker for this compressed library, Mozilla is wanting to bring transparent decompression support to Linux file-systems.

In order to do this, Dhaval Giani of Mozilla has brought a seekable zip format into the Linux kernel. His second kernel patch provides transparent decompression support into EXT4. The patch right now is "really ugly" and the decompression support hasn't been added to any other file-systems at the moment.

Some shortcomings with the current patch includes the decompression happening at a very late stage, no seek support, no mmap support, etc. To use the support, on a patched kernel the special szip user-space utility is needed to compress the fileand will then be transparently decompressed when reading the file by the kernel.

The current work on EXT4 transparent decompression can be found on the Linux kernel mailing list.