linux-kernel - [PATCH 1/2 v2] user namespace: use union in {g,u}idmap struct

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Message-Id: <20171016153054.22401-1-christian.brauner@ubuntu.com>
Date:   Mon, 16 Oct 2017 17:30:53 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     linux-kernel@...r.kernel.org
Cc:     ebiederm@...ssion.com, serge@...lyn.com, stgraber@...ntu.com,
        tycho@...ho.ws, Christian Brauner <christian.brauner@...ntu.com>
Subject: [PATCH 1/2 v2] user namespace: use union in {g,u}idmap struct

This is preparation for bumping the {g,u}idmap limits for usernamespaces.

Signed-off-by: Christian Brauner <christian.brauner@...ntu.com>
---
 include/linux/user_namespace.h | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 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
-- 
2.14.1