[PATCH v5 1/2] fs/resctrl: Report invalid domain ID when parsing io_alloc

[Aaron Tomlin]

The last_cmd_status file is intended to report details about the most
recent resctrl filesystem operation, specifically to aid in diagnosing
failures.

However, when parsing io_alloc_cbm, if a user provides a domain ID that
does not exist in the resource, the operation fails with -EINVAL without
updating last_cmd_status. This results in inconsistent behaviour where
the system call reports an error, but the status file may misleadingly
report "ok" (retained from a previous successful operation), leaving the
user unaware that the failure was caused by an invalid domain ID.

Update resctrl_io_alloc_parse_line() to explicitly write an error
message to last_cmd_status when the target domain ID cannot be found.

Suggested-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
Fixes: 28fa2cce7a83 ("fs/resctrl: Introduce interface to modify io_alloc capacity bitmasks")
Signed-off-by: Aaron Tomlin <atomlin@xxxxxxxxxxx>
---
 fs/resctrl/ctrlmondata.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/resctrl/ctrlmondata.c b/fs/resctrl/ctrlmondata.c
index b2d178d3556e..b96b661626c2 100644
--- a/fs/resctrl/ctrlmondata.c
+++ b/fs/resctrl/ctrlmondata.c
@@ -907,6 +907,7 @@ static int resctrl_io_alloc_parse_line(char *line,  struct rdt_resource *r,
 		}
 	}
 
+	rdt_last_cmd_printf("Invalid domain %lu\n", dom_id);
 	return -EINVAL;
 }
 
-- 
2.51.0