[PATCH v3 01/22] genirq: Introduce irq_get_nr_irqs() and irq_set_nr_irqs()

[Bart Van Assche <bvanassche@acm.org>]

Prepare for changing 'nr_irqs' from an exported global variable into a
variable with file scope. This will prevent accidental changes of
assignments to a local variable 'nr_irqs' into assignments to the global
'nr_irqs' variable. Suppose that a patch would be submitted for review that
removes a declaration of a local variable with the name 'nr_irqs' and that
that patch does not remove all assignments to that local variable. Such a
patch converts an assignment to a local variable into an assignment into a
global variable. If the 'nr_irqs' assignment is more than three lines away
from other changes, the assignment won't be included in the diff context
lines and hence won't be visible without inspecting the modified file. With
this patch series applied, such accidental conversions from assignments to
a local variable into an assignment to a global variable are converted into
a compilation error.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 include/linux/irqnr.h |  2 ++
 kernel/irq/irqdesc.c  | 23 +++++++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/include/linux/irqnr.h b/include/linux/irqnr.h
index 3496baa0b07f..7419b807b71b 100644
--- a/include/linux/irqnr.h
+++ b/include/linux/irqnr.h
@@ -6,6 +6,8 @@
 
 
 extern int nr_irqs;
+unsigned int irq_get_nr_irqs(void) __pure;
+unsigned int irq_set_nr_irqs(unsigned int nr);
 extern struct irq_desc *irq_to_desc(unsigned int irq);
 unsigned int irq_get_next_irq(unsigned int offset);
 
diff --git a/kernel/irq/irqdesc.c b/kernel/irq/irqdesc.c
index 1dee88ba0ae4..b0733959f8ae 100644
--- a/kernel/irq/irqdesc.c
+++ b/kernel/irq/irqdesc.c
@@ -141,6 +141,29 @@ static void desc_set_defaults(unsigned int irq, struct irq_desc *desc, int node,
 int nr_irqs = NR_IRQS;
 EXPORT_SYMBOL_GPL(nr_irqs);
 
+/**
+ * irq_get_nr_irqs() - Number of interrupts supported by the system.
+ */
+unsigned int irq_get_nr_irqs(void)
+{
+	return nr_irqs;
+}
+EXPORT_SYMBOL_GPL(irq_get_nr_irqs);
+
+/**
+ * irq_set_nr_irqs() - Set the number of interrupts supported by the system.
+ * @nr: New number of interrupts.
+ *
+ * Return: @nr.
+ */
+unsigned int irq_set_nr_irqs(unsigned int nr)
+{
+	nr_irqs = nr;
+
+	return nr;
+}
+EXPORT_SYMBOL_GPL(irq_set_nr_irqs);
+
 static DEFINE_MUTEX(sparse_irq_lock);
 static struct maple_tree sparse_irqs = MTREE_INIT_EXT(sparse_irqs,
 					MT_FLAGS_ALLOC_RANGE |