Quoting Sukadev Bhattiprolu (sukadev@xxxxxxxxxxxxxxxxxx):
>
> From: Sukadev Bhattiprolu <sukadev@xxxxxxxxxxxxxxxxxx>
> Date: Sat, 14 Mar 2009 10:21:07 -0700
> Subject: [PATCH 6/6] Explain reason for task being uncheckpointable
>
> Try to give an useful message on why a task is uncheckpointable.
As I said somewhere else, I think this is what makes it worth
having a procfile (or debugfs file) over just doing a trial
sys_checkpoint() with an invalid fd.
However,
> Signed-off-by: Sukadev Bhattiprolu <sukadev@xxxxxxxxxxxxxxxxxx>
> ---
> checkpoint/checkpoint.c | 13 +++++++++----
> fs/proc/base.c | 19 ++++++++++++++++++-
> include/linux/checkpoint.h | 7 +++++++
> 3 files changed, 34 insertions(+), 5 deletions(-)
>
> diff --git a/checkpoint/checkpoint.c b/checkpoint/checkpoint.c
> index ad0956c..c8c377d 100644
> --- a/checkpoint/checkpoint.c
> +++ b/checkpoint/checkpoint.c
> @@ -264,18 +264,23 @@ static int cr_write_all_tasks(struct cr_ctx *ctx)
> return ret;
> }
>
> -int task_checkpointable(struct task_struct *t)
> +int __task_checkpointable(struct task_struct *t)
> {
> if (t->state == TASK_DEAD) {
> pr_warning("c/r: task %d is TASK_DEAD\n", task_pid_vnr(t));
> - return 0;
> + return CR_DEAD;
> }
>
> /* Verify that task is frozen, unless it is self-checkpoint */
> if (t != current && !frozen(t))
> - return 0;
> + return CR_NOT_FROZEN;
> +
> + return CR_CHECKPOINTABLE;
> +}
>
> - return 1;
> +int task_checkpointable(struct task_struct *t)
> +{
> + return __task_checkpointable(t) == CR_CHECKPOINTABLE;
> }
>
> static int cr_may_checkpoint_task(struct task_struct *t, struct cr_ctx *ctx)
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 989ca93..6e4c07c 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -2502,9 +2502,26 @@ static int proc_pid_personality(struct seq_file *m, struct pid_namespace *ns,
> }
>
> #ifdef CONFIG_CHECKPOINT_RESTART
> +static char *explain_checkpointable(int reason)
> +{
> + char *message;
> +
> + switch(reason) {
> + case CR_CHECKPOINTABLE: message = "1"; break;
> + case CR_DEAD: message = "0 (dead)"; break;
> + case CR_NOT_FROZEN: message = "0 (not frozen)"; break;
> + default: message = "0 (unknown)"; break;
I don't think splitting it up this way is going to work long-term.
It means you need one code for each type of message, and can't give
any more detail beyond that (i.e. the value of
current->nsproxy->uts_ns.refcount, or whatever).
I think it would be better to pass a buffer into __task_checkpointable,
and let task_checkpointable() pass in a NULL buffer meaning "I
(sys_checkpoint) don't care about the explanation".
> + }
> + return message;
> +}
> +
> static int proc_pid_checkpointable(struct task_struct *task, char *buffer)
> {
> - return sprintf(buffer, "%d\n", task_checkpointable(task));
> + int rc;
> +
> + rc = __task_checkpointable(task);
> +
> + return scnprintf(buffer, PAGE_SIZE, "%s\n", explain_checkpointable(rc));
> }
> #endif
>
> diff --git a/include/linux/checkpoint.h b/include/linux/checkpoint.h
> index d1f53a6..a1eba73 100644
> --- a/include/linux/checkpoint.h
> +++ b/include/linux/checkpoint.h
> @@ -142,6 +142,13 @@ static inline int cr_enabled(void)
> return 1;
> }
>
> +enum cr_uncheckpointable_reason {
> + CR_CHECKPOINTABLE = 0,
> + CR_DEAD,
> + CR_NOT_FROZEN
> +};
> +
> +int __task_checkpointable(struct task_struct *t);
> int task_checkpointable(struct task_struct *t);
>
> #else /* !CONFIG_CHECKPOINT_RESTART */
> --
> 1.5.2.5
>
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