Re: [PATCH V2] sd: Reduce log level to KERN_NOTICE for missing caching mode page

[Alain Kalker <a.c.kalker@gmail.com>]

On 06/02/2014 08:48 PM, Alain Kalker wrote:
> Reduce the lernel log level to KERN_NOTICE for messages related
> to a missing caching mode page.

There is an open bug report at kernel.org (dating all the way back to 
Linux 2.6.34.1) about this:
Bug 16490 – "Assuming drive cache: write through" messages probably have 
wrong loglevel : https://bugzilla.kernel.org/show_bug.cgi?id=16490

Also, many people are asking questions about this on internet fora, 
submitting bug reports to bugtrackers for their distributions, 
apparently the error log level makes them think their system is 
malfunctioning in some way.

> Reasons why I think this change is justified:
> - The condition is not an error; the existing workaround of assuming
>    a write through cache doesn't limit functionality in any way.
> - It doesn't warrant a warning either: as it is most likely
>    a hardware limitation, there is little that an ordinary user can do
>    about it besides replacing the affected hardware.
>    Making it a warning would still break quiet boot (kernel commandline
>    parameter 'quiet'), and may still trip log monitoring software
>    unneccessarily, either on every boot or whenever an affected
>    external device is plugged in.
> - It should be a notice, for it is a normal but significant condition,
>    as it may impact write performance. This would bring it on par with
>    the log messages in the same function.
>
> Signed-off-by: Alain Kalker <a.c.kalker@gmail.com>
> ---
>   drivers/scsi/sd.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
> index efcbcd1..5f0f6c6 100644
> --- a/drivers/scsi/sd.c
> +++ b/drivers/scsi/sd.c
> @@ -2442,7 +2442,7 @@ sd_read_cache_type(struct scsi_disk *sdkp, unsigned char *buffer)
>   			}
>   		}
>
> -		sd_first_printk(KERN_ERR, sdkp, "No Caching mode page found\n");
> +		sd_first_printk(KERN_NOTICE, sdkp, "No Caching mode page found\n");
>   		goto defaults;
>
>   	Page_found:
> @@ -2489,7 +2489,7 @@ defaults:
>   				"Assuming drive cache: write back\n");
>   		sdkp->WCE = 1;
>   	} else {
> -		sd_first_printk(KERN_ERR, sdkp,
> +		sd_first_printk(KERN_NOTICE, sdkp,
>   				"Assuming drive cache: write through\n");
>   		sdkp->WCE = 0;
>   	}
>

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