Re: [PATCH 2/3] ata: libata: allow toggling fua parameter at runtime

[Damien Le Moal <damien.lemoal@opensource.wdc.com>]

On 10/21/22 15:21, Hannes Reinecke wrote:
> On 10/21/22 07:38, Damien Le Moal wrote:
>> From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>
>>
>> Currently, the libata.fua parameter isn't runtime-writable, so a
>> system restart is required in order to toggle it.
>> This unnecessarily complicates testing how drives behave with FUA on and
>> off.
>>
>> Let's make this parameter R/W instead, like many others in the kernel.
>>
>> Example usage:
>> Disable the parameter:
>> echo 0 >/sys/module/libata/parameters/fua
>>
>> Revalidate disk cache settings:
>> F=/sys/class/scsi_disk/0\:0\:0\:0/cache_type; echo `cat $F` >$F
>>
>> [Damien]
>> Enabling fua support by setting libata.fua to 1 will have no effect if
>> the libata module is loaded with libata.force=[ID]nofua, which disables
>> fua support for the ata device(s) identified with ID or all ata devices
>> if no ID is specified.
>>
>> Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
>> Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
>> ---
>>   drivers/ata/libata-core.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
>> index 6008f7ed1c42..1bb9616b10d9 100644
>> --- a/drivers/ata/libata-core.c
>> +++ b/drivers/ata/libata-core.c
>> @@ -128,7 +128,7 @@ module_param(atapi_passthru16, int, 0444);
>>   MODULE_PARM_DESC(atapi_passthru16, "Enable ATA_16 passthru for ATAPI devices (0=off, 1=on [default])");
>>   
>>   int libata_fua = 0;
>> -module_param_named(fua, libata_fua, int, 0444);
>> +module_param_named(fua, libata_fua, int, 0644);
>>   MODULE_PARM_DESC(fua, "FUA support (0=off [default], 1=on)");
>>   
>>   static int ata_ignore_hpa;
> Hmm. I guess you'll need to revalidate the drive when changing that; but 
> this can be done in a later patch.

Well, this is not sysfs, we cannot do this automatically easily...
And thinking about it now that you mention it, going from fua=1 to fua=0
can actually cause problems. The reverse not, since scsi side would still
see fua=0 until revalidation.

So... Unless we find a way to link the param write to reavlidation, we
should actually not allow this.
Maciej ? Thoughts ?

> 
> Reviewed-by: Hannes Reinecke <hare@suse.de>
> 
> Cheers,
> 
> Hannes

-- 
Damien Le Moal
Western Digital Research