linux-kernel - [PATCH 04/14] init: deps: order network interfaces by link order

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Date:	Sat, 17 Oct 2015 19:14:17 +0200
From:	Alexander Holler <holler@...oftware.de>
To:	linux-kernel@...r.kernel.org
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Russell King <linux@....linux.org.uk>,
	Grant Likely <grant.likely@...aro.org>,
	Alexander Holler <holler@...oftware.de>
Subject: [PATCH 04/14] init: deps: order network interfaces by link order

In order to provide stable interface numbers, network interface drivers
will be ordered by the link order. This is easy to accomplish by adding
dependencies.

Assuming three different ethernet-drivers, without any special code,
the dependency graph would not require any special order inbetween them
and would look like that:

    eth-driver-base
   /      |       \
eth-x   eth-y    eth-z

Now we just add dependencies. With the additional dependencies the graph
looks like:

 eth-driver-base
  |     | |
eth-x   | |
  |     | |
eth-y  -| |
  |       |
eth-z  ---|

Signed-off-by: Alexander Holler <holler@...oftware.de>
---
 include/linux/driver_ids.h | 11 +++++++++++
 init/dependencies.c        |  9 +++++++++
 2 files changed, 20 insertions(+)

diff --git a/include/linux/driver_ids.h b/include/linux/driver_ids.h
index 60964fe..1133a68 100644
--- a/include/linux/driver_ids.h
+++ b/include/linux/driver_ids.h
@@ -15,6 +15,17 @@
 enum {
 	drvid_unused,
 	/* To be filled */
+
+	/*
+	 * Network drivers will be ordered according to the link order
+	 * (which means not necessarily according to their appearance
+	 * here).
+	 * This provides stable interface numbers.
+	 * Therefor their IDs have to be in the following block.
+	 */
+	drvid_network_drivers_start,
+	drvid_network_drivers_end,
+
 	drvid_max
 };
 
diff --git a/init/dependencies.c b/init/dependencies.c
index b484f67..027fc4b 100644
--- a/init/dependencies.c
+++ b/init/dependencies.c
@@ -301,12 +301,21 @@ static int __init add_dependencies(void)
 static void __init build_inventory(void)
 {
 	const struct _annotated_initcall *ac;
+	unsigned id_last_network_driver = 0;
 
 	ac = __annotated_initcall_start;
 	for (; ac < __annotated_initcall_end; ++ac) {
 		include_node[ac->id] = true;
 		annotated_initcall_by_drvid[ac->id] = ac;
 		nvertices = max(nvertices, ac->id);
+		/* order network drivers by link order*/
+		if (ac->id > drvid_network_drivers_start &&
+				ac->id < drvid_network_drivers_end) {
+			if (id_last_network_driver)
+				add_initcall_dependency(ac->id,
+					id_last_network_driver);
+			id_last_network_driver = ac->id;
+		}
 	}
 }
 
-- 
2.1.0

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