Re: [PATCH resend] mmc: Added ioctl to let userspace apps send ACMDs

[Arnd Bergmann <arnd@arndb.de>]

On Saturday 19 March 2011, John Calixto wrote:

> > > -static int mmc_app_cmd(struct mmc_host *host, struct mmc_card *card)
> > > +int mmc_app_cmd(struct mmc_host *host, struct mmc_card *card)
> > >  {
> > >         int err;
> > >         struct mmc_command cmd;
> > > @@ -48,6 +48,7 @@ static int mmc_app_cmd(struct mmc_host *host, struct mmc_card *card)
> > >
> > >         return 0;
> > >  }
> > > +EXPORT_SYMBOL(mmc_app_cmd);
> >
> > Why not EXPORT_SYMBOL_GPL?
> >
> 
> I was just using the convention already used in sd_ops.c.  I can send a
> pre-patch that sets all of the symbol exports in that file to be
> EXPORT_SYMBOL_GPL, but without confirmation from you and others on this
> list, that seems like overstepping my "jurisdiction".  Is that preferable?

No, you shouldn't change existing symbols, we normally don't do that.
Some subsystems in the kernel generally allow regular EXPORT_SYMBOL
for everything, I don't know if that's the case here.

Chris, do you prefer to leave the new export as EXPORT_SYMBOL
along wiht the others or to use EXPORT_SYMBOL_GPL?

> > As I mentioned, any ioctl command that gets introduced needs to be
> > designed very carefully to make sure we don't need to change it in the
> > future. The only two things I can see here are:
> >
> > * The struct_version should be removed
> > * The data pointer is not compatible between 32 and 64 bits.
> >   One solution for this would be to make it a __u64 argument
> >   and require the user to cast the pointer to a 64 bit type.
> 
> I don't understand your comment about the data pointer not being
> compatible between 32 and 64 bits.  Wouldn't the compiler take care of
> pointer size?

The problem is when you have a 64 bit kernel that can run both
32 and 64 bit user applications. The compiler for the 32 bit user
process will create a smaller data structure than what a 64 bit
kernel expects. The two options here are to force the compiler
to use a compatible layout, or to use the compat_ioctl() function
to convert from one format to the other.

	Arnd