Re: [PATCH V3] asm-generic: add a generic uaccess.h

Arnd Bergmann
2009-05-01T14:06:08Z

On Friday 01 May 2009, Michal Simek wrote:
> Arnd Bergmann wrote:
> > +
> > +#include <asm/segment.h>
> > +
> > +#ifndef get_fs
> > +#define MAKE_MM_SEG(s) ((mm_segment_t) { (s) })
>
> one line above -> get_fs could be defined in different space
> and this arch could use MAKE_MM_SEG too -> for example powerpc.

I don't think I understand what you are trying to tell me.
How do you think this should look?

> > +
> > +#define VERIFY_READ 0
> > +#define VERIFY_WRITE 1
> > +
>
>
> Not sure if any arch do READ/WRITE check but if yes.

I could not find any architecture using it either, but the
API is defined this way.

> #ifndef access_ok
>
> > +#define access_ok(type, addr, size) __access_ok((unsigned long)(addr),(size))
>
> #endif

right, will change.

> > +
> > +/*
> > + * The architecture should really override this if possible, at least
> > + * doing a check on the get_fs()
> > + */
>
> If they should really override it but why write it here.

Mostly for documentation purposes, so that an architecture maintainer
can copy the prototype. I see the asm-generic headers as both fallbacks
for architectures and as templates of what should be implemented.

> > +#define get_user(x, ptr) \
> > +({ \
> > + might_sleep(); \
> > + __access_ok(ptr, sizeof (*ptr)) ? \
> > + __get_user(x, ptr) : \
> > + -EFAULT; \
> > +})
>
> I am getting here (for put_user macro too) any error on noMMU. :-(

What kind of error do you see?

> > +static inline long
> > +strncpy_from_user(char *dst, const char __user *src, long count)
> > +{
> > + if (!__access_ok(src, 1))
> > + return -EFAULT;
> > + return __strncpy_from_user(dst, src, count);
> > +}
>
> Is it a good place to add might_sleep() and unlikely(+ some other cases) too?
> We have almost the same code.

Yes, I think so. The unlikely() can probably go into __access_ok() though,
so we don't have to write it every time.