On Wed, 2016-08-03 at 10:31 +0300, Ville Syrjälä wrote:
> On Tue, Aug 02, 2016 at 09:42:07PM -0700, Rodrigo Vivi wrote:
> >
> > A read(fd, buf, len) function should return the number
> > of bytes read. In our case we need to return the
> > number of bytes we copy to user, instead of returning
> > the number of bytes we read internally.
> >
> > It was really strange when I saw i-g-t test case using
> > len '54' but getting '56' as return. First thought was
> > how do we read more than we asked? But also I checked
> > and there was really only 54. Until I realized it
> > was all our fault. EFAULT!
> >
> > Signed-off-by: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
> > ---
> > drivers/gpu/drm/i915/i915_debugfs.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_debugfs.c
> > b/drivers/gpu/drm/i915/i915_debugfs.c
> > index 7052c47..b7b8d79 100644
> > --- a/drivers/gpu/drm/i915/i915_debugfs.c
> > +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> > @@ -3659,7 +3659,7 @@ i915_pipe_crc_read(struct file *filep, char
> > __user *user_buf, size_t count,
> >
> > spin_unlock_irq(&pipe_crc->lock);
> >
> > - return bytes_read;
> > + return PIPE_CRC_LINE_LEN;
> Nope. We can read multiple entries in one go.
>
> bytes_read += snprintf()
>
> so it's mostly good. The only case where it fails if we don't have
> enough space for the snprintf(), as snprintf() will then return the
> number of bytes it would have written. That can actually happen on
> account of the hex vs. decimal mess with the frame counter.
Oh, I see.
So what about:
if (bytes_read > count)
return -E-something?
>
> >
> > }
> >
> > static const struct file_operations i915_pipe_crc_fops = {
> > --
> > 2.5.5
> >
> > _______________________________________________
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> > Intel-gfx@xxxxxxxxxxxxxxxxxxxxx
> > https://lists.freedesktop.org/mailman/listinfo/intel-gfx
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