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

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

On 10/21/22 17:45, Hannes Reinecke wrote:
> On 10/21/22 10:00, Damien Le Moal wrote:
>> On 10/21/22 15:50, Damien Le Moal wrote:
>>> 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 ?
>>
>> I looked at this a little more. We could define the operations (struct
>> kernel_param_ops) manually together with the fua parameter declaration,
>> but that would be really ugly...
>>
>> Given that we are switching to fua=1 by default, do you still need a
>> dynamic argument ? I am now thinking that this patch should be dropped.
>>
> I'd kill it, and let users it handle via blacklist flags only.

Yep, with the default set to 1 that is the goal. I kept the fua module
parameter for backward compatibility, in case some setups out there use
it. But the force=[ID]nofua or force=[ID]fua module parameters should be
the preferred way to control this now.

> 
> Cheers,
> 
> Hannes

-- 
Damien Le Moal
Western Digital Research