linux-kernel - [PATCH 1/2 v5] user namespace: use union in {g,u}idmap struct

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Date:   Sun, 22 Oct 2017 20:40:35 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     linux-kernel@...r.kernel.org
Cc:     serge@...lyn.com, stgraber@...ntu.com, tycho@...ho.ws,
        Christian Brauner <christian.brauner@...ntu.com>
Subject: [PATCH 1/2 v5] user namespace: use union in {g,u}idmap struct

- Add a struct containing two pointer to extents and wrap both the static extent
  array and the struct into a union. This is done in preparation for bumping the
  {g,u}idmap limits for user namespaces.
- Add brackets around anonymous union when using designated initializers to
  initialize members in order to please gcc <= 4.4.

Signed-off-by: Christian Brauner <christian.brauner@...ntu.com>
---
Changelog 2017-10-22:
* no changes

Changelog 2017-10-19:
* kernel/user.c: Use brackets around anonymous union when using designated
  initializers to initialize members. This is done to please gcc <= 4.4.
---
 include/linux/user_namespace.h | 18 +++++++++++++-----
 kernel/user.c                  | 30 ++++++++++++++++++------------
 2 files changed, 31 insertions(+), 17 deletions(-)

diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index c18e01252346..7c83d7f6289b 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -12,13 +12,21 @@
 
 #define UID_GID_MAP_MAX_EXTENTS 5
 
+struct uid_gid_extent {
+	u32 first;
+	u32 lower_first;
+	u32 count;
+};
+
 struct uid_gid_map {	/* 64 bytes -- 1 cache line */
 	u32 nr_extents;
-	struct uid_gid_extent {
-		u32 first;
-		u32 lower_first;
-		u32 count;
-	} extent[UID_GID_MAP_MAX_EXTENTS];
+	union {
+		struct uid_gid_extent extent[UID_GID_MAP_MAX_EXTENTS];
+		struct {
+			struct uid_gid_extent *forward;
+			struct uid_gid_extent *reverse;
+		};
+	};
 };
 
 #define USERNS_SETGROUPS_ALLOWED 1UL
diff --git a/kernel/user.c b/kernel/user.c
index 00281add65b2..9a20acce460d 100644
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -26,26 +26,32 @@
 struct user_namespace init_user_ns = {
 	.uid_map = {
 		.nr_extents = 1,
-		.extent[0] = {
-			.first = 0,
-			.lower_first = 0,
-			.count = 4294967295U,
+		{
+			.extent[0] = {
+				.first = 0,
+				.lower_first = 0,
+				.count = 4294967295U,
+			},
 		},
 	},
 	.gid_map = {
 		.nr_extents = 1,
-		.extent[0] = {
-			.first = 0,
-			.lower_first = 0,
-			.count = 4294967295U,
+		{
+			.extent[0] = {
+				.first = 0,
+				.lower_first = 0,
+				.count = 4294967295U,
+			},
 		},
 	},
 	.projid_map = {
 		.nr_extents = 1,
-		.extent[0] = {
-			.first = 0,
-			.lower_first = 0,
-			.count = 4294967295U,
+		{
+			.extent[0] = {
+				.first = 0,
+				.lower_first = 0,
+				.count = 4294967295U,
+			},
 		},
 	},
 	.count = ATOMIC_INIT(3),
-- 
2.14.1