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    Subject[RFC v12][PATCH 11/14] External checkpoint of a task other than ourself
    Date
    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.

    Changelog[v12]:
    - Replace obsolete cr_debug() with pr_debug()

    Changelog[v11]:
    - Copy contents of 'init->fs->root' instead of pointing to them

    Changelog[v10]:
    - Grab vfs root of container init, rather than current process

    Signed-off-by: Oren Laadan <orenl@cs.columbia.edu>
    Acked-by: Serge Hallyn <serue@us.ibm.com>
    ---
    checkpoint/checkpoint.c | 72 ++++++++++++++++++++++++++++++++++++++++++-
    checkpoint/restart.c | 4 +-
    checkpoint/sys.c | 6 ++++
    include/linux/checkpoint.h | 2 +
    4 files changed, 80 insertions(+), 4 deletions(-)

    diff --git a/checkpoint/checkpoint.c b/checkpoint/checkpoint.c
    index dd0f527..e0af8a2 100644
    --- a/checkpoint/checkpoint.c
    +++ b/checkpoint/checkpoint.c
    @@ -10,6 +10,7 @@

    #include <linux/version.h>
    #include <linux/sched.h>
    +#include <linux/ptrace.h>
    #include <linux/time.h>
    #include <linux/fs.h>
    #include <linux/file.h>
    @@ -225,6 +226,13 @@ 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;
    + }
    +
    ret = cr_write_task_struct(ctx, t);
    pr_debug("task_struct: ret %d\n", ret);
    if (ret < 0)
    @@ -247,22 +255,82 @@ static int cr_write_task(struct cr_ctx *ctx, struct task_struct *t)
    return ret;
    }

    +static int cr_get_container(struct cr_ctx *ctx, pid_t pid)
    +{
    + struct task_struct *task = NULL;
    + struct nsproxy *nsproxy = NULL;
    + int err = -ESRCH;
    +
    + ctx->root_pid = pid;
    +
    + 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_task = task;
    + ctx->root_nsproxy = nsproxy;
    +
    + return 0;
    +
    + out:
    + if (task)
    + put_task_struct(task);
    + return err;
    +}
    +
    +/* setup checkpoint-specific parts of ctx */
    static int cr_ctx_checkpoint(struct cr_ctx *ctx, pid_t pid)
    {
    struct fs_struct *fs;
    + int ret;

    ctx->root_pid = pid;

    + ret = cr_get_container(ctx, pid);
    + if (ret < 0)
    + return ret;
    +
    /*
    * assume checkpointer is in container's root vfs
    * FIXME: this works for now, but will change with real containers
    */

    - fs = current->fs;
    + task_lock(ctx->root_task);
    + fs = ctx->root_task->fs;
    read_lock(&fs->lock);
    ctx->fs_mnt = fs->root;
    path_get(&ctx->fs_mnt);
    read_unlock(&fs->lock);
    + task_unlock(ctx->root_task);

    return 0;
    }
    @@ -277,7 +345,7 @@ int do_checkpoint(struct cr_ctx *ctx, pid_t pid)
    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/restart.c b/checkpoint/restart.c
    index ece05b7..0c46abf 100644
    --- a/checkpoint/restart.c
    +++ b/checkpoint/restart.c
    @@ -277,7 +277,7 @@ static int cr_read_task(struct cr_ctx *ctx)
    }

    /* setup restart-specific parts of ctx */
    -static int cr_ctx_restart(struct cr_ctx *ctx)
    +static int cr_ctx_restart(struct cr_ctx *ctx, pid_t pid)
    {
    return 0;
    }
    @@ -286,7 +286,7 @@ int do_restart(struct cr_ctx *ctx, pid_t pid)
    {
    int ret;

    - ret = cr_ctx_restart(ctx);
    + ret = cr_ctx_restart(ctx, pid);
    if (ret < 0)
    goto out;
    ret = cr_read_head(ctx);
    diff --git a/checkpoint/sys.c b/checkpoint/sys.c
    index a506b3a..4a51ed3 100644
    --- a/checkpoint/sys.c
    +++ b/checkpoint/sys.c
    @@ -9,6 +9,7 @@
    */

    #include <linux/sched.h>
    +#include <linux/nsproxy.h>
    #include <linux/kernel.h>
    #include <linux/fs.h>
    #include <linux/file.h>
    @@ -163,6 +164,11 @@ static void cr_ctx_free(struct cr_ctx *ctx)
    cr_pgarr_free(ctx);
    cr_objhash_free(ctx);

    + if (ctx->root_nsproxy)
    + put_nsproxy(ctx->root_nsproxy);
    + if (ctx->root_task)
    + put_task_struct(ctx->root_task);
    +
    kfree(ctx);
    }

    diff --git a/include/linux/checkpoint.h b/include/linux/checkpoint.h
    index ea9ab4c..cf54f47 100644
    --- a/include/linux/checkpoint.h
    +++ b/include/linux/checkpoint.h
    @@ -19,6 +19,8 @@ struct cr_ctx {
    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 */
    --
    1.5.4.3


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