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

[christos%astron.com@localhost (Christos Zoulas)]

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.

christos