Re: [PATCH 03/10] RDMA: Add ib_respond_udata()

[Jason Gunthorpe <jgg@nvidia.com>]

On Fri, Feb 13, 2026 at 11:48:13AM -0400, Jason Gunthorpe wrote:
> On Fri, Feb 13, 2026 at 05:37:39PM +0200, Leon Romanovsky wrote:
> > On Fri, Feb 13, 2026 at 08:43:59AM -0400, Jason Gunthorpe wrote:
> > > On Fri, Feb 13, 2026 at 12:10:53PM +0200, Leon Romanovsky wrote:
> > > > > @@ -3177,6 +3177,38 @@ static inline int _ib_copy_validate_udata_in(struct ib_udata *udata, void *req,
> > > > >  		ret;                                                          \
> > > > >  	})
> > > > >  
> > > > > +static inline int _ib_respond_udata(struct ib_udata *udata, const void *src,
> > > > > +				   size_t len)
> > > > > +{
> > > > > +	size_t copy_len;
> > > > > +
> > > > > +	copy_len = min(len, udata->outlen);
> > > > 
> > > > Don't you need to check that udata->outlen is larger than zero?
> > > 
> > > As far as I can tell 0 works fine with copy_to_user()
> > 
> > My main concern that it is not clear what return value will be in that
> > case.
> > 
> > +       copy_len = min(len, udata->outlen);
> > +       if (copy_to_user(udata->outbuf, src, copy_len))
> > +               return -EFAULT; <--- this?
> > +       if (copy_len < udata->outlen) {
> > ...
> > +       }
> > +       return 0; <- or this?
> 
> Oh, yeah, that's a really good point.

So it still returns 0, copy_to_user() returns the number of bytes left
to copy. See Documentation/kernel-hacking/hacking.rst

    Unlike :c:func:`put_user()` and :c:func:`get_user()`, they
    return the amount of uncopied data (ie. 0 still means success).

Number of bytes left to copy for a 0 length copy is still 0, not
EFAULT.

I'm just going to add a comment.

Jason