Re: [PATCH 1/7] staging: comedi: comedi_compat32.c: fix COMEDI_CMD copy back

[Ian Abbott]

On 27/01/15 17:20, Hartley Sweeten wrote:
> On Tuesday, January 27, 2015 8:59 AM, Ian Abbott wrote:
> > On 27/01/15 15:50, Ian Abbott wrote:
> > > `do_cmd_ioctl()` in "comedi_fops.c" handles the `COMEDI_CMD` ioctl.
> > > This returns `-EAGAIN` if it has copied a modified `struct comedi_cmd`
> > > back to user-space.  (This occurs when the low-level Comedi driver's
> > > `do_cmdtest()` handler returns non-zero to indicate a problem with the
> > > contents of the `struct comedi_cmd`, or when the `struct comedi_cmd` has
> > > the `CMDF_BOGUS` flag set.)
> > >
> > > `compat_cmd()` in "comedi_compat32.c" handles the 32-bit compatible
> > > version of the `COMEDI_CMD` ioctl.  Currently, it never copies a 32-bit
> > > compatible version of `struct comedi_cmd` back to user-space, which is
> > > at odds with the way the regular `COMEDI_CMD` ioctl is handled.  To fix
> > > it, change `compat_cmd()` to copy a 32-bit compatible version of the
> > > `struct comedi_cmd` back to user-space when the main ioctl handler
> > > returns `-EAGAIN`.
> > >
> > > Signed-off-by: Ian Abbott <abbotti@xxxxxxxxx>
> > > Cc: <stable@xxxxxxxxxxxxxxx>
> > > ---
> > >    drivers/staging/comedi/comedi_compat32.c | 13 +++++++++++--
> > >    1 file changed, 11 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/staging/comedi/comedi_compat32.c b/drivers/staging/comedi/comedi_compat32.c
> > > index 5a4c74f..2440c60 100644
> > > --- a/drivers/staging/comedi/comedi_compat32.c
> > > +++ b/drivers/staging/comedi/comedi_compat32.c
> > > @@ -262,7 +262,8 @@ static int compat_cmd(struct file *file, unsigned long arg)
> > >    {
> > >    	struct comedi_cmd __user *cmd;
> > >    	struct comedi32_cmd_struct __user *cmd32;
> > > -	int rc;
> > > +	long rc;
> > > +	int err;
> >
> > Gah!  That change in type of the 'rc' variable resulted from me changing
> > the order of the patches in the series.  It still works, but looks a bit
> > out of place.  Should I post an updated version without this niggle?
>
> Please fix it. I does look strange. Actually, the last patch looks strange.
>
> The "normal" return type in the kernel is an 'int'. As you mention in the
> commit message: "The `unlocked_ioctl` and `compat_ioctl` file operations
> are both defined to return a `long` (I don't know why)." It seems cleaner
> to just have all the static functions return an int and just have
> comedi_compat_ioctl() return the long value. Maybe just add a comment
> why...
>
> My 2 cents...

Yes, on reflection I think passing through the `long` return value is 
just pandering to an abomination that should be ignored.  I'll post a v2 
series with the above niggle fixed and the final patch dropped.

--
-=( Ian Abbott @ MEV Ltd.    E-mail: <abbotti@xxxxxxxxx> )=-
-=(                          Web: http://www.mev.co.uk/  )=-
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