This is fine, but I have one suggestion.

In each place which casts char * into the structure, verify the alignment. This might be not strictly needed right now, since from what I see the pointers are malloced, but might help if the code starts mutating in future. I am not sure whether the checks should be asserts or silently return error.

In D9225#190692, @kib wrote:

This is fine, but I have one suggestion.

In each place which casts char * into the structure, verify the alignment. This might be not strictly needed right now, since from what I see the pointers are malloced, but might help if the code starts mutating in future. I am not sure whether the checks should be asserts or silently return error.

Sure, that seems like a good idea. I wasn't too concerned about it because the code takes care to keep struct extattrs (and contents) 8-byte aligned -- and I don't think we require greater alignment outside of e.g. SSE/AVX values.