[RFC][PATCH 1/5] uts namespaces: Implement utsname namespaces

["Serge E. Hallyn" <serue@us.ibm.com>]

This patch defines the uts namespace and some manipulators.
Adds the uts namespace to task_struct, and initializes a
system-wide init namespace which will continue to be used when
it makes sense.

Signed-off-by: Serge E. Hallyn <serue@us.ibm.com>
---
 include/linux/init_task.h |    2 +
 include/linux/sched.h     |    2 +
 include/linux/utsname.h   |   40 +++++++++++++++++++++++++-
 init/Kconfig              |    8 +++++
 init/version.c            |   70 ++++++++++++++++++++++++++++++++++++++++-----
 kernel/exit.c             |    2 +
 kernel/fork.c             |    9 +++++-
 7 files changed, 122 insertions(+), 11 deletions(-)

14c326d603d88d9ed40a1ddafbf23fc3da68a645
diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 41ecbb8..21b1751 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -3,6 +3,7 @@
 
 #include <linux/file.h>
 #include <linux/rcupdate.h>
+#include <linux/utsname.h>
 
 #define INIT_FDTABLE \
 {							\
@@ -123,6 +124,7 @@ extern struct group_info init_groups;
 	.journal_info	= NULL,						\
 	.cpu_timers	= INIT_CPU_TIMERS(tsk.cpu_timers),		\
 	.fs_excl	= ATOMIC_INIT(0),				\
+	.uts_ns		= &init_uts_ns,					\
 }
 
 
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 541f482..97c7990 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -684,6 +684,7 @@ static inline void prefetch_stack(struct
 
 struct audit_context;		/* See audit.c */
 struct mempolicy;
+struct uts_namespace;
 
 enum sleep_type {
 	SLEEP_NORMAL,
@@ -807,6 +808,7 @@ struct task_struct {
 	struct files_struct *files;
 /* namespace */
 	struct namespace *namespace;
+	struct uts_namespace *uts_ns;
 /* signal handlers */
 	struct signal_struct *signal;
 	struct sighand_struct *sighand;
diff --git a/include/linux/utsname.h b/include/linux/utsname.h
index 13e1da0..cc28ac5 100644
--- a/include/linux/utsname.h
+++ b/include/linux/utsname.h
@@ -1,5 +1,8 @@
 #ifndef _LINUX_UTSNAME_H
 #define _LINUX_UTSNAME_H
+#include <linux/sched.h>
+#include <linux/kref.h>
+#include <asm/atomic.h>
 
 #define __OLD_UTS_LEN 8
 
@@ -30,7 +33,42 @@ struct new_utsname {
 	char domainname[65];
 };
 
-extern struct new_utsname system_utsname;
+struct uts_namespace {
+	struct kref kref;
+	struct new_utsname name;
+};
+extern struct uts_namespace init_uts_ns;
+
+#ifdef CONFIG_UTS_NS
+
+extern struct uts_namespace *clone_uts_ns(struct uts_namespace *old_ns);
+extern struct uts_namespace *unshare_uts_ns(void);
+extern void free_uts_ns(struct kref *kref);
+
+static inline void get_uts_ns(struct uts_namespace *ns)
+{
+	kref_get(&ns->kref);
+}
+
+static inline void put_uts_ns(struct uts_namespace *ns)
+{
+	kref_put(&ns->kref, free_uts_ns);
+}
+
+#else
+static inline void get_uts_ns(struct uts_namespace *ns)
+{
+}
+static inline void put_uts_ns(struct uts_namespace *ns)
+{
+}
+#endif
+
+static inline struct new_utsname *utsname(void)
+{
+	return &current->uts_ns->name;
+}
+
 
 extern struct rw_semaphore uts_sem;
 #endif
diff --git a/init/Kconfig b/init/Kconfig
index 3b36a1d..8460e5a 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -166,6 +166,14 @@ config SYSCTL
 	  building a kernel for install/rescue disks or your system is very
 	  limited in memory.
 
+config UTS_NS
+	bool "UTS Namespaces"
+	default n
+	help
+	  Support uts namespaces.  This allows containers, i.e.
+	  vservers, to use uts namespaces to provide different
+	  uts info for different servers.  If unsure, say N.
+
 config AUDIT
 	bool "Auditing support"
 	depends on NET
diff --git a/init/version.c b/init/version.c
index 3ddc3ce..e128d72 100644
--- a/init/version.c
+++ b/init/version.c
@@ -11,22 +11,76 @@
 #include <linux/uts.h>
 #include <linux/utsname.h>
 #include <linux/version.h>
+#include <linux/sched.h>
 
 #define version(a) Version_ ## a
 #define version_string(a) version(a)
 
 int version_string(LINUX_VERSION_CODE);
 
-struct new_utsname system_utsname = {
-	.sysname	= UTS_SYSNAME,
-	.nodename	= UTS_NODENAME,
-	.release	= UTS_RELEASE,
-	.version	= UTS_VERSION,
-	.machine	= UTS_MACHINE,
-	.domainname	= UTS_DOMAINNAME,
+struct uts_namespace init_uts_ns = {
+	.kref = {
+		.refcount	= ATOMIC_INIT(2),
+	},
+	.name = {
+		.sysname	= UTS_SYSNAME,
+		.nodename	= UTS_NODENAME,
+		.release	= UTS_RELEASE,
+		.version	= UTS_VERSION,
+		.machine	= UTS_MACHINE,
+		.domainname	= UTS_DOMAINNAME,
+	},
 };
 
-EXPORT_SYMBOL(system_utsname);
+#ifdef CONFIG_UTS_NS
+/*
+ * Clone a new ns copying an original utsname, setting refcount to 1
+ * @old_ns: namespace to clone
+ * Return NULL on error (failure to kmalloc), new ns otherwise
+ */
+struct uts_namespace *clone_uts_ns(struct uts_namespace *old_ns)
+{
+	struct uts_namespace *ns;
+
+	ns = kmalloc(sizeof(struct uts_namespace), GFP_KERNEL);
+	if (ns) {
+		memcpy(&ns->name, &old_ns->name, sizeof(ns->name));
+		kref_init(&ns->kref);
+	}
+	return ns;
+}
+
+/*
+ * unshare the current process' utsname namespace.  Changes
+ * to the utsname of this process won't be seen by parent, and
+ * vice versa
+ *
+ * Return NULL on error (failure to kmalloc), new ns otherwise
+ *
+ * TODO: decide where this should be locked  (depends on how/where
+ * we decide to use this)
+ */
+struct uts_namespace *unshare_uts_ns(void)
+{
+	struct uts_namespace *old_ns = current->uts_ns;
+	struct uts_namespace *new_ns = clone_uts_ns(old_ns);
+	if (new_ns) {
+		current->uts_ns = new_ns;
+		put_uts_ns(old_ns);
+	}
+	return new_ns;
+}
+EXPORT_SYMBOL(unshare_uts_ns);
+
+void free_uts_ns(struct kref *kref)
+{
+	struct uts_namespace *ns;
+
+	ns = container_of(kref, struct uts_namespace, kref);
+	kfree(ns);
+}
+EXPORT_SYMBOL(free_uts_ns);
+#endif
 
 const char linux_banner[] =
 	"Linux version " UTS_RELEASE " (" LINUX_COMPILE_BY "@"
diff --git a/kernel/exit.c b/kernel/exit.c
index 6c2eeb8..97c5405 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -34,6 +34,7 @@
 #include <linux/mutex.h>
 #include <linux/futex.h>
 #include <linux/compat.h>
+#include <linux/utsname.h>
 
 #include <asm/uaccess.h>
 #include <asm/unistd.h>
@@ -173,6 +174,7 @@ repeat:
 	spin_unlock(&p->proc_lock);
 	proc_pid_flush(proc_dentry);
 	release_thread(p);
+	put_uts_ns(p->uts_ns);
 	call_rcu(&p->rcu, delayed_put_task_struct);
 
 	p = leader;
diff --git a/kernel/fork.c b/kernel/fork.c
index 3384eb8..62e4479 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -44,6 +44,7 @@
 #include <linux/rmap.h>
 #include <linux/acct.h>
 #include <linux/cn_proc.h>
+#include <linux/utsname.h>
 
 #include <asm/pgtable.h>
 #include <asm/pgalloc.h>
@@ -1119,6 +1120,8 @@ static task_t *copy_process(unsigned lon
 	/* Perform scheduler related setup. Assign this task to a CPU. */
 	sched_fork(p, clone_flags);
 
+	get_uts_ns(p->uts_ns);
+
 	/* Need tasklist lock for parent etc handling! */
 	write_lock_irq(&tasklist_lock);
 
@@ -1158,7 +1161,7 @@ static task_t *copy_process(unsigned lon
 		spin_unlock(&current->sighand->siglock);
 		write_unlock_irq(&tasklist_lock);
 		retval = -ERESTARTNOINTR;
-		goto bad_fork_cleanup_namespace;
+		goto bad_fork_cleanup_utsns;
 	}
 
 	if (clone_flags & CLONE_THREAD) {
@@ -1171,7 +1174,7 @@ static task_t *copy_process(unsigned lon
 			spin_unlock(&current->sighand->siglock);
 			write_unlock_irq(&tasklist_lock);
 			retval = -EAGAIN;
-			goto bad_fork_cleanup_namespace;
+			goto bad_fork_cleanup_utsns;
 		}
 
 		p->group_leader = current->group_leader;
@@ -1223,6 +1226,8 @@ static task_t *copy_process(unsigned lon
 	proc_fork_connector(p);
 	return p;
 
+bad_fork_cleanup_utsns:
+	put_uts_ns(p->uts_ns);
 bad_fork_cleanup_namespace:
 	exit_namespace(p);
 bad_fork_cleanup_keys:
-- 
1.2.4