Maxim,

According to http://fxr.watson.org/fxr/ident?im=bigexcerpts;i=SO_ACCEPTFILTER, SO_ACCEPTFILTER is defined as 0x1000, and I see this:

23235 1 nginx CALL setsockopt(7,0xffff,0x1000,0x7f7fffffd410,0x100)
23235 1 nginx RET setsockopt 0

From the manpage:

RETURN VALUES
A 0 is returned if the call succeeds, -1 if it fails.

Regards,

Hugo