genirq/msi: Provide struct msi_map

A simple struct to hold a MSI index / Linux interrupt number pair. It will
be returned from the dynamic vector allocation function and handed back to
the corresponding free() function.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20221124232326.326410494@linutronix.de

include/linux/msi_api.h

@@ -18,6 +18,19 @@ enum msi_domain_ids {
 	MSI_MAX_DEVICE_IRQDOMAINS,
 };
 
+/**
+ * msi_map - Mapping between MSI index and Linux interrupt number
+ * @index:	The MSI index, e.g. slot in the MSI-X table or
+ *		a software managed index if >= 0. If negative
+ *		the allocation function failed and it contains
+ *		the error code.
+ * @virq:	The associated Linux interrupt number
+ */
+struct msi_map {
+	int	index;
+	int	virq;
+};
+
 unsigned int msi_domain_get_virq(struct device *dev, unsigned int domid, unsigned int index);
 
 /**