[RFC v8][PATCH 11/12] External checkpoint of a task other than ourself

Oren Laadan
2008-10-30T13:51:14Z

Now we can do "external" checkpoint, i.e. act on another task.

sys_checkpoint() now looks up the target pid (in our namespace) and
checkpoints that corresponding task. That task should be the root of
a container.

sys_restart() remains the same, as the restart is always done in the
context of the restarting task.

Signed-off-by: Oren Laadan <orenl@cs.columbia.edu>
---
checkpoint/checkpoint.c | 4 ++-
checkpoint/sys.c | 71 ++++++++++++++++++++++++++++++++++++++++++-
include/linux/checkpoint.h | 5 ++-
3 files changed, 76 insertions(+), 4 deletions(-)

diff --git a/checkpoint/checkpoint.c b/checkpoint/checkpoint.c
index ce622e1..f636958 100644
--- a/checkpoint/checkpoint.c
+++ b/checkpoint/checkpoint.c
@@ -190,6 +190,8 @@ static int cr_write_task(struct cr_ctx *ctx, struct task_struct *t)
{
int ret ;

+ /* TODO: verity that the task is frozen (unless self) */
+
if (t->state == TASK_DEAD) {
pr_warning("C/R: task may not be in state TASK_DEAD\n");
return -EAGAIN;
@@ -227,7 +229,7 @@ int do_checkpoint(struct cr_ctx *ctx)
ret = cr_write_head(ctx);
if (ret < 0)
goto out;
- ret = cr_write_task(ctx, current);
+ ret = cr_write_task(ctx, ctx->root_task);
if (ret < 0)
goto out;
ret = cr_write_tail(ctx);
diff --git a/checkpoint/sys.c b/checkpoint/sys.c
index c57ae96..3421d47 100644
--- a/checkpoint/sys.c
+++ b/checkpoint/sys.c
@@ -9,6 +9,8 @@
*/

#include <linux/sched.h>
+#include <linux/nsproxy.h>
+#include <linux/ptrace.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/file.h>
@@ -152,6 +154,66 @@ void cr_hbuf_put(struct cr_ctx *ctx, int n)
* restart operation, and persists until the operation is completed.
*/

+static void cr_ctx_put_container(struct cr_ctx *ctx)
+{
+ if (ctx->root_nsproxy)
+ put_nsproxy(ctx->root_nsproxy);
+ if (ctx->root_task)
+ put_task_struct(ctx->root_task);
+ ctx->root_pid = 0;
+}
+
+static int cr_ctx_get_container(pid_t pid, struct cr_ctx *ctx)
+{
+ struct task_struct *task = NULL;
+ struct nsproxy *nsproxy = NULL;
+ int err = -ESRCH;
+
+ read_lock(&tasklist_lock);
+ task = find_task_by_vpid(pid);
+ if (task)
+ get_task_struct(task);
+ read_unlock(&tasklist_lock);
+
+ if (!task)
+ goto out;
+
+#if 0 /* enable to use containers */
+ if (!is_container_init(task)) {
+ err = -EINVAL;
+ goto out;
+ }
+#endif
+
+ if (!ptrace_may_access(task, PTRACE_MODE_READ)) {
+ err = -EPERM;
+ goto out;
+ }
+
+ rcu_read_lock();
+ if (task_nsproxy(task)) {
+ nsproxy = task_nsproxy(task);
+ get_nsproxy(nsproxy);
+ }
+ rcu_read_unlock();
+
+ if (!nsproxy)
+ goto out;
+
+ /* TODO: verify that the container is frozen */
+
+ ctx->root_pid = pid;
+ ctx->root_task = task;
+ ctx->root_nsproxy = nsproxy;
+
+ return 0;
+
+ out:
+ if (task)
+ put_task_struct(task);
+ return err;
+}
+
/* unique checkpoint identifier (FIXME: should be per-container) */
static atomic_t cr_ctx_count = ATOMIC_INIT(0);

@@ -168,6 +230,8 @@ static void cr_ctx_free(struct cr_ctx *ctx)
cr_pgarr_free(ctx);
cr_objhash_free(ctx);

+ cr_ctx_put_container(ctx);
+
kfree(ctx);
}

@@ -180,7 +244,6 @@ static struct cr_ctx *cr_ctx_alloc(pid_t pid, int fd, unsigned long flags)
if (!ctx)
return ERR_PTR(-ENOMEM);

- ctx->pid = pid;
ctx->flags = flags;

INIT_LIST_HEAD(&ctx->pgarr_list);
@@ -190,6 +253,10 @@ static struct cr_ctx *cr_ctx_alloc(pid_t pid, int fd, unsigned long flags)
if (!ctx->file)
goto err;

+ err = cr_ctx_get_container(pid, ctx);
+ if (err < 0)
+ goto err;
+
err = -ENOMEM;
ctx->hbuf = kmalloc(CR_HBUF_TOTAL, GFP_KERNEL);

@@ -205,7 +272,7 @@ static struct cr_ctx *cr_ctx_alloc(pid_t pid, int fd, unsigned long flags)
* assume checkpointer is in container's root vfs
* FIXME: this works for now, but will change with real containers
*/
- ctx->vfsroot = &current->fs->root;
+ ctx->vfsroot = &ctx->root_task->fs->root;
path_get(ctx->vfsroot);

ctx->crid = atomic_inc_return(&cr_ctx_count);
diff --git a/include/linux/checkpoint.h b/include/linux/checkpoint.h
index 6c1e87f..e9d554e 100644
--- a/include/linux/checkpoint.h
+++ b/include/linux/checkpoint.h
@@ -16,9 +16,12 @@
#define CR_VERSION 2

struct cr_ctx {
- pid_t pid; /* container identifier */
int crid; /* unique checkpoint id */

+ pid_t root_pid; /* container identifier */
+ struct task_struct *root_task; /* container root task */
+ struct nsproxy *root_nsproxy; /* container root nsproxy */
+
unsigned long flags;
unsigned long oflags; /* restart: old flags */