Why use `thread' as an argument of Syscalls?

[MingyanGuo]

On 6/5/06, Daniel Eischen <deischen at freebsd.org> wrote:
>
> On Mon, 5 Jun 2006, MingyanGuo wrote:
>
> > Hi all,
> >    I  find that  FreeBSD Syscalls  always have an `thread'
> > argument, for example, preadv(/sys/kern/sys_generic.c)
> > has a `td' argument.  But  some Syscalls may rarely  use
> > this argument,  and  thay ( and functions they invoke) can
> > get  the  `thread'  who  make  the  Syscall  _easily_  via
> > `curthread' macro if  needed. So the `thread' argument
> > seems not needed.
> >  Can anybody tell me why use `thread' as an argument
> > of Syscalls?
>
> You could have asked "why use 'proc' as an argument of Syscalls"
> 12 years ago (or more).  When the kernel became thread-aware
> (almost 5 years ago), most 'struct proc' arguments were changed
> to 'struct thread'.
>
> --
> DE
>

They are the same questions, I think ;-). Now would
you please explain  "why use `proc' as  an  argument
of Syscalls"  to me :)?  I've  read some source code
of the kernel, but no comments about it found.
Thanks.
Regards,

-- 
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the longing for love, the search for knowledge, and unbearable pity for
the suffering of mankind.
                         ---------Bertrand Russell