Re: [PATCH] s390: speedup strn{cpy,len} from user.

[Arnd Bergmann]

Andrew Morton <akpm@xxxxxxxx> schrieb am 12.06.2004, 00:19:18:
> Martin Schwidefsky  wrote:
> >  static inline long
> >  strncpy_from_user(char *dst, const char *src, long count)
> >  {
> >          long res = -EFAULT;
> >          might_sleep();
> > -        if (access_ok(VERIFY_READ, src, 1))
> > -                res = __strncpy_from_user_asm(dst, src, count);
> > +        if (access_ok(VERIFY_READ, src, 1)) {
> > +                res = __strncpy_from_user_asm(count, dst, src);
> > +	}
> >          return res;
> >  }
> 
> Shouldn't the access_ok() check be passed `count', rather than `1'?

No, AFAIU, the logic in strncpy_from_user is that it succeeds for any
string that is limited by either 'count' or a trailing zero or the end
of the user mapping, whichever comes first. This means only one
byte needs to be addressable.

On s390, it doesn't matter anyway because access_ok() is always true,
but the check for access_ok() is the same on all architectures.

       Arnd <><
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