Re: [PATCH v2] drivers/cdrom: improved ioctl for media change detection

[Randy Dunlap]

On 9/8/21 5:17 PM, Phillip Potter wrote:
> > > +static int cdrom_ioctl_timed_media_change(struct cdrom_device_info *cdi,
> > > +		unsigned long arg)
> > > +{
> > > +	int ret;
> > > +	struct cdrom_timed_media_change_info __user *info;
> > > +	struct cdrom_timed_media_change_info tmp_info;
> > > +
> > > +	if (!CDROM_CAN(CDC_MEDIA_CHANGED))
> > > +		return -ENOSYS;
> > > +
> > > +	info = (struct cdrom_timed_media_change_info __user *)arg;
> > > +	cd_dbg(CD_DO_IOCTL, "entering CDROM_TIMED_MEDIA_CHANGE\n");
> > > +
> > > +	ret = cdrom_ioctl_media_changed(cdi, CDSL_CURRENT);
> > > +	if (ret < 0)
> > > +		return ret;
> > > +
> > > +	if (copy_from_user(&tmp_info, info, sizeof(tmp_info)) != 0)
> > > +		return -EFAULT;
> > > +
> > > +	tmp_info.has_changed = ((tmp_info.last_media_change - cdi->last_media_change_ms) < 0);
> Dear Christoph,
>
> Sorry didn't see this e-mail before I replied to Lukas, so I hope you
> don't think I was ignoring you :-)
>
> > Overly long line here, but more importantly this is much cleaner with
> > a good old if:
> >
> >
> > 	if (tmp_info.last_media_change - cdi->last_media_change_ms) < 0)
> > 		tmp_info.has_changed = 1;
>
> Whilst I don't disagree this is technically cleaner, the existing style
> certainly read well to me. In terms of line length, checkpatch doesn't
> complain about it, so I guess you mean purely from a visual perspective?

Documentation/process/coding-style.rst says:

  The preferred limit on the length of a single line is 80 columns.

checkpatch only checks lines > 100 columns since that is OK in a few
cases, like a long quoted string.

So try to limit line lengths to 80 columns unless there is some
other reason not to do that.

> > > +{
> > > +	__s64	last_media_change;	/* Timestamp of the last detected media
> > > +					 * change in ms. May be set by caller, updated
> > > +					 * upon successful return of ioctl.
> > > +					 */
> > > +	__u64	has_changed;		/* Set to 1 by ioctl if last detected media
> >
> > More overly long lines.  Also why is has_changed a u64 if it is used as
> > a boolean flag?

Might as well be explicit about it and also make it obvious that there
is some space available for other fields.

thanks.
--
~Randy