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

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Date:   Tue, 7 Sep 2021 07:35:25 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Lukas Prediger <lumip@...ip.de>
Cc:     axboe@...nel.dk, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] drivers/cdrom: improved ioctl for media change
 detection

> +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);

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;

> +{
> +	__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?