linux-kernel - Re: [PATCH 1/2] md: Add configurability for consistency check feature

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Date:	Tue, 18 Mar 2014 09:54:56 +1100
From:	NeilBrown <neilb@...e.de>
To:	Ralph Mueck <linux-kernel@...eck.de>
Cc:	i4passt@...ts.cs.fau.de, linux-raid@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Matthias Oefelein <ma.oefelein@...or.de>
Subject: Re: [PATCH 1/2] md: Add configurability for consistency check
 feature

On Mon, 17 Mar 2014 16:00:04 +0100 Ralph Mueck <linux-kernel@...eck.de> wrote:

> This patch adds sysfs configurability for the md level-1 RAID
> consistency check.
> The feature introduces a new attribute in sysfs named "safe_read".
> To toggle consistency checks on/off, simply echo safe_read in
> /sys/block/md*/md/safe_read.
> 
> Signed-off-by: Ralph Mueck <linux-kernel@...eck.de>
> Signed-off-by: Matthias Oefelein <ma.oefelein@...or.de>
> 
> ---
>  drivers/md/md.c | 27 +++++++++++++++++++++++++++
>  drivers/md/md.h |  3 +++
>  2 files changed, 30 insertions(+)
> 
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 4ad5cc4..5cc9a00 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -4652,6 +4652,32 @@ static struct md_sysfs_entry md_array_size =
>  __ATTR(array_size, S_IRUGO|S_IWUSR, array_size_show,
>         array_size_store);
>  
> +static ssize_t
> +safe_read_show(struct mddev *mddev, char *page)
> +{
> +	if(mddev->safe_read)
> +		return sprintf(page, "enabled\n");
> +	else
> +		return sprintf(page, "disabled\n");
> +}
> +
> +static ssize_t
> +safe_read_store(struct mddev *mddev, const char *buf, size_t len)
> +{
> +	if(mddev->pers->level != 1) {
> +		printk(KERN_NOTICE "RAID level not supported!\n");
> +		return len;
> +	}
> +	if (strncmp(buf, "safe_read", 9) == 0) {
> +		mddev->safe_read = !mddev->safe_read;
> +	}
> +	return len;
> +}
> +

So let me get this straight....

There is a sysfs file called "safe_read".
When you read from that file it reports either "enabled" or "disabled".

However you cannot write "enabled" or "disabled" to the file.  Rather you
write "safe_read".  And when you do, it toggles the status.

Seriously?

Any chance you could use device_show_bool / device_store_bool ??

NeilBrown



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