sgs4ext4fs is a tiny tool to work with ext4 images for the i9500

Unlike other devices (like the i9505) that just need a recent version
of make_ext4fs from ext4_utils from the latest Android source -- and 
optinally the correct file_contexts reference for SELinux -- the
i9500 expects some extra bytes in its image files. 

There are 4 bytes padded to both the file header as well as every chunk 
header. In Samsung built images, these bytes are non-zero, though I've 
not been able to determine their meaning (yet). They're not chunk
checksums, that's for sure. Anyway, setting them to zero seems to
work fine.

This tool can list chunks and extra bytes (--list option), add extra
bytes to the image (--bloat option), or strip the extra bytes from the 
image (--trim option). when bloating, the tool just adds zeroes in 
the right places.

Works for me so far, hope it works for you as well ...

-Chainfire