fs/resctrl: Add "*" shorthand to set io_alloc CBM for all domains

Hi Babu, Tony, Reinette,

This series addresses two limitations in the fs/resctrl io_alloc interface:
inconsistent error reporting and the lack of a mechanism for bulk configuration.

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. Patch 1 addresses this by writing an error message to last_cmd_status when the target domain ID cannot be found.

Configuring the io_alloc_cbm interface requires an explicit domain ID for each cache domain. On systems with high core counts and numerous cache clusters, this requirement becomes cumbersome for automation and management tasks that aim to apply a uniform policy. Patch 2 introduces a wildcard domain ID selector "*" for the io_alloc_cbm interface. This enables users to set the same Capacity Bitmask (CBM) across all cache domains in a single operation.

Please let me know your thoughts.

Changes since v5 [1]:
- Corrected the subject line in Patch 1 to accurately reference "io_alloc_cbm" instead of "io_alloc" (Reinette Chatre)

- Refined both commit messages for strict accuracy and conciseness, including correcting the description of last_cmd_status behaviour and removing redundant examples (Reinette Chatre)

- Reordered commit tags in Patch 1 to place the Fixes: tag at the top in accordance with maintainer guidelines (Reinette Chatre)

- Updated the wildcard documentation to include a caveat regarding systems that do not require consecutive bits (Reinette Chatre)

- Initialised parsing variables (dom_id, update_all) at declaration to eliminate uninitialised state flows (Reinette Chatre)

- Added robust validation to immediately reject any configurations trailing a global wildcard (e.g., "*=f;1=f") (Reinette Chatre)

Changes since v4 [2]:
- Split the submission into a two-patch series to separate the fix from the new feature (Reinette Chatre)

- Refactored resctrl_io_alloc_parse_line() to prioritise the dom check before string comparison, preventing potential NULL pointer dereference (Reinette Chatre)

- Restructured commit messages to strictly follow the "Context, Problem, Solution" format (Reinette Chatre)

- Updated the documentation to include the result of the modification (Babu Moger)

- Updated the commit description to avoid implying that '0' is a universal minimum CBM (Reinette Chatre)

Changes since v3 [3]:
- Updated the wildcard documentation text to be clearer and less prescriptive (Reinette Chatre)

- Reverted the while loop refactoring in resctrl_io_alloc_parse_line() to restore the standard parsing pattern and prevent invalid domain ID regressions (Reinette Chatre)

- Added explicit validation to ensure the wildcard selector is followed by a value assignment (Reinette Chatre)

- Restored memcpy() usage for configuration copying to minimise unrelated diff noise

Changes since v2 [4]:
- Dropped return -EINVAL for a missing seq_show implementation (Reinette Chatre)
- Dropped helpers to check io_alloc support and enabled state (Reinette Chatre)
- Removed additional complexity (Babu Moger)
- Introduced the "*" wildcard for io_alloc_cbm to allow updating all cache domains (Reinette Chatre)
- Replaced goto-based line parsing with a while loop to support multi-domain and wildcard iterations
- Replaced memcpy() with direct structure assignment

Changes since v1 [5]:
- Updated each helper for consistency (Babu Moger)
- Refactored the loop logic in function resctrl_io_alloc_parse_line() to improve readability
- Added inline keyword to each helper
- Added inline keyword to function parse_domain_cbm()

[1]: https://lore.kernel.org/lkml/[email protected]/
[2]: https://lore.kernel.org/lkml/[email protected]/
[3]: https://lore.kernel.org/lkml/[email protected]/
[4]: https://lore.kernel.org/lkml/[email protected]/
[5]: https://lore.kernel.org/lkml/[email protected]/

Aaron Tomlin (2):
fs/resctrl: Report invalid domain ID when parsing io_alloc_cbm fs/resctrl: Add "*" shorthand to set io_alloc CBM for all domains

 Documentation/filesystems/resctrl.rst |  8 ++++++++
 fs/resctrl/ctrlmondata.c              | 22 ++++++++++++++++++----
 2 files changed, 26 insertions(+), 4 deletions(-)

2.51.0

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.

---
 fs/resctrl/ctrlmondata.c | 1 +
 1 file changed, 1 insertion(+)

index cc4237c57cbe..2ef53161ce11 100644
@@ -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

Hi Aaron,

Thank you.

Reinette

Configuring the io_alloc_cbm interface requires an explicit domain ID for each cache domain. On systems with high core counts and numerous cache clusters, this requirement becomes cumbersome for automation and management tasks that aim to apply a uniform policy.

Introduce a wildcard domain ID selector "*" for the io_alloc_cbm interface. This enables users to set the same Capacity Bitmask (CBM) across all cache domains in a single operation.

---
 Documentation/filesystems/resctrl.rst |  8 ++++++++
 fs/resctrl/ctrlmondata.c              | 21 +++++++++++++++++----
 2 files changed, 25 insertions(+), 4 deletions(-)

index ba609f8d4de5..b003bed339fd 100644
@@ -215,6 +215,14 @@ related to allocation:
 			# cat /sys/fs/resctrl/info/L3/io_alloc_cbm
 			0=00ff;1=000f
 
+		An ID of "*" configures all domains with the provided CBM.
+
+		Example on a system that does not require a minimum number of consecutive bits in the mask::
+
+			# echo "*=0" > /sys/fs/resctrl/info/L3/io_alloc_cbm
+			# cat /sys/fs/resctrl/info/L3/io_alloc_cbm
+			0=0;1=0
+
 		When CDP is enabled "io_alloc_cbm" associated with the CDP_DATA and CDP_CODE
 		resources may reflect the same values. For example, values read from and
 		written to /sys/fs/resctrl/info/L3DATA/io_alloc_cbm may be reflected by

index 2ef53161ce11..9a7dfc48cb2e 100644
@@ -954,25 +954,34 @@ static int resctrl_io_alloc_parse_line(char *line,  struct rdt_resource *r,
 				       struct resctrl_schema *s, u32 closid)
 {
 	enum resctrl_conf_type peer_type;
+	unsigned long dom_id = ULONG_MAX;
 	struct rdt_parse_data data;
 	struct rdt_ctrl_domain *d;
+	bool update_all = false;
 	char *dom = NULL, *id;
-	unsigned long dom_id;
 
 next:
 	if (!line || line[0] == '\0')
 		return 0;
 
+	if (update_all) {
+		rdt_last_cmd_puts("Configurations after global '*'\n");
+		return -EINVAL;
+	}
+
 	dom = strsep(&line, ";");
 	id = strsep(&dom, "=");
-	if (!dom || kstrtoul(id, 10, &dom_id)) {
+
+	if (dom && !strcmp(id, "*")) {
+		update_all = true;
+	} else if (!dom || kstrtoul(id, 10, &dom_id)) {
 		rdt_last_cmd_puts("Missing '=' or non-numeric domain\n");
 		return -EINVAL;
 	}
 
 	dom = strim(dom);
 	list_for_each_entry(d, &r->ctrl_domains, hdr.list) {
-		if (d->hdr.id == dom_id) {
+		if (update_all || d->hdr.id == dom_id) {
 			data.buf = dom;
 			data.mode = RDT_MODE_SHAREABLE;
 			data.closid = closid;

@@ -988,10 +997,14 @@ static int resctrl_io_alloc_parse_line(char *line,  struct rdt_resource *r,
 				       &d->staged_config[s->conf_type],
 				       sizeof(d->staged_config[0]));
 			}
-			goto next;
+			if (!update_all)
+				goto next;
 		}
 	}
 
+	if (update_all)
+		goto next;
+
 	rdt_last_cmd_printf("Invalid domain %lu\n", dom_id);
 	return -EINVAL;
 }

2.51.0

Hi Aaron,

Thank you.

Reinette

Looks good to me.