[PATCH v6 1/2] fs/resctrl: Report invalid domain ID when parsing io_alloc_cbm

[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 returns an error, but last_cmd_status misleadingly reports
"ok", leaving the user unaware that the failure was caused by an invalid
domain ID.

Write an error message to last_cmd_status when the target domain ID cannot
be found.

Fixes: 28fa2cce7a83 ("fs/resctrl: Introduce interface to modify io_alloc capacity bitmasks")
Suggested-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
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 cc4237c57cbe..2ef53161ce11 100644
--- a/fs/resctrl/ctrlmondata.c
+++ b/fs/resctrl/ctrlmondata.c
@@ -992,6 +992,7 @@ 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