svn commit: r205014 - in head: . sys/amd64/amd64 sys/amd64/conf sys/amd64/include sys/amd64/linux32 sys/compat/freebsd32 sys/compat/ia32 sys/conf sys/fs/procfs sys/ia64/conf sys/ia64/ia64 sys/ia64/...

[John Baldwin]

On Saturday 13 March 2010 02:19:32 pm M. Warner Losh wrote:
> In message: <20100313170725.GW8200 at hoeg.nl>
> 
>             Ed Schouten <ed at 80386.nl> writes:
> : * M. Warner Losh <imp at bsdimp.com> wrote:
> : > that sounds like a good idea.  But it isn't as simple as changing all
> : > the COMPAT_FREEBSDX in the .c code.  There's also hooks in the syscall
> : > glue generation that would be affected.
> :
> : Hmmm... Indeed.
> :
> : I thought a bit more about this and I realized it would be better if we
> : wouldn't use a FreeBSD major number for this, but the actual
> : __FreeBSD_version.
> 
> Hmmm, that might be harder.  The problem is that when I want to run a
> program from FreeBSD 3.0, I may need an interface that was in 3.0, but
> was removed prior to 5.0 shipping.  This means the kernel needs the
> COMPAT_FREEBSD4 option right now to work.  So things are kind of
> confusing.

This isn't completely theoretical.  Old (<= 4.x) i386 binaries use the 
foosys() methods for SYSV IPC (e.g. msgsys()) rather than msgget, msgctl, 
etc., so this is a case that would have to be correctly handled by any new 
organization of these options.  I do think it makes the most sense to have the 
setting be the oldest major rev, and I also think that using __FreeBSD_version 
values rather than major versions would be too fine-grained (not very user-
friendly).  It would also enforce the rule of mandating COMPAT_FREEBSD4 
implying COMPAT_FREEBSD5, etc.  It just means you can't try to build a 
stripped kernel that only includes FreeBSD4 support without including FreeBSD5 
(which is a way to solve Warner's problem).  Trying to enumerate "ranges" of 
supported compat releases would be too confusing and error-prone I think.

Also, the syscall generation bit would not be that hard.  You would just 
replace the code that generates '#ifdef COMPAT_FREEBSD4' with '#if 
FREEBSD_COMPAT_VERSION <= 4'.  Of course, you would probably want to special 
case version 0 so that you could remove all compat support if the option isn't 
defined, so it would maybe have to be '#if define(FREEBSD_COMPAT_VERSION) && 
FREEBSD_COMPAT_VERSION <= 4'.

-- 
John Baldwin