[PATCH] c/r: Add UTS support (v4)

[Dan Smith <danms-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>]

This patch adds a "phase" of checkpoint that saves out information about any
namespaces the task(s) may have.  Do this by tracking the namespace objects
of the tasks and making sure that tasks with the same namespace that follow
get properly referenced in the checkpoint stream.  Note that for now, we
refuse to checkpoint if all tasks in the set don't share the same set of
*all* namespaces.

Restart is handled in userspace by reading the UTS record(s), calling
unshare() and setting the hostname accordingly.  See my changes to
mktree.c for details.

I tested this with single and multiple task restore, on top of Oren's
v13 tree.

Changes:
  - Remove the kernel restore path
  - Punt on nested namespaces
  - Use __NEW_UTS_LEN in nodename and domainname buffers
  - Add a note to Documentation/checkpoint/internals.txt to indicate where
    in the save/restore process the UTS information is kept
  - Store (and track) the objref of the namespace itself instead of the
    nsproxy (based on comments from Dave on IRC)
  - Remove explicit check for non-root nsproxy
  - Store the nodename and domainname lengths and use cr_write_string()
    to store the actual name strings

Signed-off-by: Dan Smith <danms-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
Cc: adobriyan-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
Cc: orenl-eQaUEPhvms7ENvBUuze7eA@public.gmane.org
---
 Documentation/checkpoint/internals.txt |    2 +
 checkpoint/checkpoint.c                |   80 ++++++++++++++++++++++++++++++++
 checkpoint/objhash.c                   |    7 +++
 checkpoint/restart.c                   |    1 +
 include/linux/checkpoint.h             |    1 +
 include/linux/checkpoint_hdr.h         |   14 ++++++
 6 files changed, 105 insertions(+), 0 deletions(-)

diff --git a/Documentation/checkpoint/internals.txt b/Documentation/checkpoint/internals.txt
index b363e83..7a2488b 100644
--- a/Documentation/checkpoint/internals.txt
+++ b/Documentation/checkpoint/internals.txt
@@ -12,6 +12,8 @@ The order of operations, both save and restore, is as follows:
 
 * Process forest: [TBD] tasks and their relationships
 
+* Namespace section: per-container namespace information
+
 * Per task data (for each task):
   -> task state: elements of task_struct
   -> thread state: elements of thread_struct and thread_info
diff --git a/checkpoint/checkpoint.c b/checkpoint/checkpoint.c
index 64155de..228bdae 100644
--- a/checkpoint/checkpoint.c
+++ b/checkpoint/checkpoint.c
@@ -193,6 +193,82 @@ static int cr_write_tail(struct cr_ctx *ctx)
 	return ret;
 }
 
+static int cr_write_ns_uts(struct cr_ctx *ctx, struct task_struct *t)
+{
+	struct cr_hdr h;
+	struct cr_hdr_utsns *hh = cr_hbuf_get(ctx, sizeof(*hh));
+	struct new_utsname *n = &t->nsproxy->uts_ns->name;
+	int ret;
+
+	h.type = CR_HDR_UTSNS;
+	h.len = sizeof(*hh);
+	h.parent = 0;
+
+	hh->nodename_len = sizeof(n->nodename);
+	hh->domainname_len = sizeof(n->domainname);
+
+	ret = cr_write_obj(ctx, &h, hh);
+	if (ret < 0)
+		goto out;
+
+	ret = cr_write_string(ctx, n->nodename, hh->nodename_len);
+	if (ret < 0)
+		goto out;
+
+	ret = cr_write_string(ctx, n->domainname, hh->domainname_len);
+ out:
+	cr_hbuf_put(ctx, sizeof(*hh));
+
+	return ret;
+}
+
+static int cr_write_namespaces(struct cr_ctx *ctx, struct task_struct *t)
+{
+	struct cr_hdr h;
+	struct cr_hdr_namespaces *hh = cr_hbuf_get(ctx, sizeof(*hh));
+	struct nsproxy *nsp = t->nsproxy;
+	int ret;
+
+	h.type = CR_HDR_NS;
+	h.len = sizeof(*hh);
+	h.parent = 0;
+
+	hh->types = 0;
+
+	if (cr_obj_add_ptr(ctx, nsp->uts_ns, &hh->uts_ref, CR_OBJ_UTSNS, 0))
+		hh->types |= CR_NS_UTS;
+
+	ret = cr_write_obj(ctx, &h, hh);
+	if (ret)
+		goto out;
+
+	if (hh->types & CR_NS_UTS) {
+		ret = cr_write_ns_uts(ctx, t);
+		if (ret < 0)
+			goto out;
+
+		/* FIXME: Write other namespaces here */
+	}
+ out:
+	cr_hbuf_put(ctx, sizeof(*hh));
+
+	return ret;
+}
+
+static int cr_write_all_namespaces(struct cr_ctx *ctx)
+{
+	int n, ret = 0;
+
+	for (n = 0; n < ctx->tasks_nr; n++) {
+		pr_debug("dumping ns for task #%d\n", n);
+		ret = cr_write_namespaces(ctx, ctx->tasks_arr[n]);
+		if (ret < 0)
+			break;
+	}
+
+	return ret;
+}
+
 /* dump the task_struct of a given task */
 static int cr_write_task_struct(struct cr_ctx *ctx, struct task_struct *t)
 {
@@ -549,6 +625,10 @@ int do_checkpoint(struct cr_ctx *ctx, pid_t pid)
 	if (ret < 0)
 		goto out;
 
+	ret = cr_write_all_namespaces(ctx);
+	if (ret < 0)
+		goto out;
+
 	ret = cr_write_all_tasks(ctx);
 	if (ret < 0)
 		goto out;
diff --git a/checkpoint/objhash.c b/checkpoint/objhash.c
index ee31b38..afcf1d1 100644
--- a/checkpoint/objhash.c
+++ b/checkpoint/objhash.c
@@ -12,6 +12,7 @@
 #include <linux/file.h>
 #include <linux/hash.h>
 #include <linux/checkpoint.h>
+#include <linux/utsname.h>
 
 struct cr_objref {
 	int objref;
@@ -35,6 +36,9 @@ static void cr_obj_ref_drop(struct cr_objref *obj)
 	case CR_OBJ_FILE:
 		fput((struct file *) obj->ptr);
 		break;
+	case CR_OBJ_UTSNS:
+		put_uts_ns((struct uts_namespace *) obj->ptr);
+		break;
 	default:
 		BUG();
 	}
@@ -46,6 +50,9 @@ static void cr_obj_ref_grab(struct cr_objref *obj)
 	case CR_OBJ_FILE:
 		get_file((struct file *) obj->ptr);
 		break;
+	case CR_OBJ_UTSNS:
+		get_uts_ns((struct uts_namespace *) obj->ptr);
+		break;
 	default:
 		BUG();
 	}
diff --git a/checkpoint/restart.c b/checkpoint/restart.c
index 7ec4de4..0ed01aa 100644
--- a/checkpoint/restart.c
+++ b/checkpoint/restart.c
@@ -15,6 +15,7 @@
 #include <linux/magic.h>
 #include <linux/checkpoint.h>
 #include <linux/checkpoint_hdr.h>
+#include <linux/utsname.h>
 
 #include "checkpoint_arch.h"
 
diff --git a/include/linux/checkpoint.h b/include/linux/checkpoint.h
index 217cf6e..02c2990 100644
--- a/include/linux/checkpoint.h
+++ b/include/linux/checkpoint.h
@@ -75,6 +75,7 @@ extern void cr_ctx_put(struct cr_ctx *ctx);
 
 enum {
 	CR_OBJ_FILE = 1,
+	CR_OBJ_UTSNS,
 	CR_OBJ_MAX
 };
 
diff --git a/include/linux/checkpoint_hdr.h b/include/linux/checkpoint_hdr.h
index 6dc739f..886ab53 100644
--- a/include/linux/checkpoint_hdr.h
+++ b/include/linux/checkpoint_hdr.h
@@ -49,6 +49,8 @@ enum {
 	CR_HDR_TASK,
 	CR_HDR_THREAD,
 	CR_HDR_CPU,
+	CR_HDR_NS,
+	CR_HDR_UTSNS,
 
 	CR_HDR_MM = 201,
 	CR_HDR_VMA,
@@ -156,4 +158,16 @@ struct cr_hdr_fd_data {
 	__u64 f_version;
 } __attribute__((aligned(8)));
 
+#define CR_NS_UTS 1
+
+struct cr_hdr_namespaces {
+	__u32 types;   /* NS records that follow this */
+	__u32 uts_ref; /* Objref of matching UTS namespace */
+};
+
+struct cr_hdr_utsns {
+	__u32 nodename_len;
+	__u32 domainname_len;
+};
+
 #endif /* _CHECKPOINT_CKPT_HDR_H_ */
-- 
1.5.6.3