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

[Hannes Reinecke <hare@suse.de>]

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.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		           Kernel Storage Architect
hare@suse.de			                  +49 911 74053 688
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