Re: netbsd32 emulation in driver open() or read()

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Mon, Aug 29, 2011 at 04:28:00PM +0000, Christos Zoulas wrote:
> In article <20110829151339.GA24766%asim.lip6.fr@localhost>,
> Manuel Bouyer  <bouyer%antioche.eu.org@localhost> wrote:
> >Hello,
> >I'm working on getting bpf(4) in a 64bit kernel play with a 32bit userland.
> >I've translated the ioctls, but I'm now stuck with read().
> >read(2) on a bpf device returns wire packets (no problems with this)
> >with a bpf-specific header in front of each packet. This bpf header is:
> >struct bpf_hdr {
> >        struct bpf_timeval bh_tstamp;   /* time stamp */
> >     uint32_t        bh_caplen;      /* length of captured portion */
> >     uint32_t        bh_datalen;     /* original length of packet */
> >     uint16_t        bh_hdrlen;      /* length of bpf header (this struct
> >                                        plus alignment padding) */
> >};
> >with:
> >struct bpf_timeval {
> >        long tv_sec;
> >     long tv_usec;
> >};
> >
> >and this is the problem (sizeof(bpf_timeval) changes).
> >It doens't look easy to just move struct bpf_timeval to fixed-size types
> >(compat issues, I guess this would require a rename of open() or read()).
> >On the other hand, if bpf(4) did know if the program doing the
> >open() syscall is 32 or 64bits, it could appends the right header
> >(could also be done in read() but it's less easy: it would require
> >translating an existing buffer; while flagging it at open() time
> >allows to build the right buffer from start).
> >So: is there a way to know if the emulation used by a userland program
> >doing an open() is 32 or 64bit ?
> 
> Yes, look at PK_32 in the process flags. If you are going to do this, please
> look at what FreeBSD did with bpf_ts/bpf_xhdr and the time format changes
> and do the same (provide timespec/bintime etc). This is how they handle
> compatibility mode too.

This is related to the BIOCSTSTAMP ioctl isn't it ? I can see how it's used
in kernel but I couldn't find it in userland. So, to me it looks like
the old bpf_hdr is used most of the time ...
I'm not sure if it's worth implementing BIOCSTSTAMP (and we have to assure
compat for bpf_hdr anyway)

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--