LWN: Comments on "A reworked BPF API"

A reworked BPF API

PaXTeam — Sun, 27 Jul 2014 19:34:48 +0000

what is the meaning of a negative attr_len and insn_idx?

A reworked BPF API

adamgundy — Fri, 25 Jul 2014 16:16:53 +0000

wasn't there a requirement that all new system calls should have a 'flags' argument?

A reworked BPF API

samroberts — Thu, 24 Jul 2014 20:28:41 +0000

Isn't it more likely that the silence reflects a lack of usage?

A reworked BPF API

neilbrown — Thu, 24 Jul 2014 02:37:43 +0000

That "fixup" mechanism seems vaguely reminiscent of something that "binder" does.
binder doesn't use fds, but it has similar numeric handles not unlike the "watch descriptors" that inotify uses.

A "binder_buffer" (which holds a message) contains some data and then some "offsets".
The "offsets" are references into the data part of the buffer where "flat_binder_object"s are stored, which contain a type, some flags and an object identifier.
Based on the the type, some transformation is performed on the object identifier to convert between "remote" and "local" references. (see switch (fp->type) in binder_transaction()).

This is much the same as converting between kernel-internal pointers and user-space fd numbers.