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

From: Phillip Potter
Date: Wed Sep 08 2021 - 20:17:46 EST


> > +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?

> > +{
> > + __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?

As this is not a packed struct, would not a smaller value still take up
the same space?

As I'm keen to grow as a maintainer and take feedback, I can certainly
wait for Lukas to reply to this for sure.

Regards,
Phil