linux-kernel - [PATCH RFC cpumask 3/5] cpumask: Add a "none" alias to complement "all"

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Date:   Tue,  5 Jan 2021 16:49:54 -0800
From:   paulmck@...nel.org
To:     linux-kernel@...r.kernel.org
Cc:     peterz@...radead.org, yury.norov@...il.com, kernel-team@...com,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        "Paul E . McKenney" <paulmck@...nel.org>
Subject: [PATCH RFC cpumask 3/5] cpumask: Add a "none" alias to complement "all"

From: Paul Gortmaker <paul.gortmaker@...driver.com>

With global support for a CPU list alias of "all", it seems to just make
sense to also trivially extend support for an opposite "none" specifier.

Signed-off-by: Paul Gortmaker <paul.gortmaker@...driver.com>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 Documentation/admin-guide/kernel-parameters.rst | 6 ++++++
 lib/cpumask.c                                   | 5 +++++
 2 files changed, 11 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.rst b/Documentation/admin-guide/kernel-parameters.rst
index cdf4e81..7dd1224 100644
--- a/Documentation/admin-guide/kernel-parameters.rst
+++ b/Documentation/admin-guide/kernel-parameters.rst
@@ -76,6 +76,12 @@ is equivalent to "foo_cpus=0-N" -- where "N" is the numerically last CPU on
 the system, thus avoiding looking up the value in "/sys/devices/system/cpu"
 in advance on each deployed system.
 
+        foo_cpus=none
+
+will provide an empty/cleared cpu mask for the associated boot argument.
+
+Note that "all" and "none" are not necessarily valid/sensible input values
+for each available parameter expecting a CPU list.
 
 This document may not be entirely up to date and comprehensive. The command
 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
diff --git a/lib/cpumask.c b/lib/cpumask.c
index 9f8ff72..7fbcab8 100644
--- a/lib/cpumask.c
+++ b/lib/cpumask.c
@@ -110,6 +110,11 @@ int cpulist_parse(const char *buf, struct cpumask *dstp)
 		return 0;
 	}
 
+	if (!strcmp(buf, "none")) {
+		cpumask_clear(dstp);
+		return 0;
+	}
+
 	return bitmap_parselist(buf, cpumask_bits(dstp), nr_cpumask_bits);
 }
 EXPORT_SYMBOL(cpulist_parse);
-- 
2.9.5