Re: [PATCH 10/11] fs/resctrl: Change last_cmd_status custom during input parsing

[Ben Horgan]

Hi Reinette,

On 3/2/26 18:46, Reinette Chatre wrote:
> A pattern of usage of last_cmd_status was introduced during its enabling in
> commit
> 
> c377dcfbee80 ("x86/intel_rdt: Add diagnostics when writing the schemata file")
> 
> and since copied throughout resctrl to result in the following custom:
> 
> 	..._write()
> 	{
> 		/* Early parsing of input, exit on failure. */
> 
> 		/* Obtain rdtgroup_mutex */
> 		rdt_last_cmd_clear(); /* Clear last_cmd_status buffer */
> 
> 		/*
> 		 * Act on user command, failures result in detail
> 		 * error message in last_cmd_status buffer via
> 		 * rdt_last_cmd_puts()/rdt_last_cmd_printf().
> 		 */
> 
> 		/* Release rdtgroup_mutex */
> 	}
> 
> If resctrl exits with failure during early parsing of input there are two
> possible scenarios:
>  - The last_cmd_status buffer is empty and a user's read of
>    info/last_cmd_status returns "ok".
>  - The last_cmd_status buffer contains details from an earlier ...write()
>    failure and a user's read of info/last_cmd_status returns this outdated
>    error description.
> 
> Writing to a resctrl file is considered a "resctrl command" and the
> resctrl documentation states the following about the last_cmd_status file:
>    "If the command failed, it will provide more information that can be
>     conveyed in the error returns from file operations."
> Neither of the current scenarios is correct behavior.
> 
> Move early input parsing to be done with rdtgroup_mutex held after the
> last_cmd_status buffer is cleared. Let info/last_cmd_status be accurate
> when an error is encountered during parsing of user command.

This seems useful and the patch looks good to me.

Reviewed-by: Ben Horgan <ben.horgan@xxxxxxx>

Thanks,

Ben