Re: [RFC PATCH 4/5] use next syscall data to change the behavior of IPC_SET

["Serge E. Hallyn" <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>]

Quoting Nadia.Derbey-6ktuUTfB/bM@public.gmane.org (Nadia.Derbey-6ktuUTfB/bM@public.gmane.org):
> [PATCH 04/05]
> 
> This patch uses the value written into the next_syscall_data proc file
> as a flag to change the way msgctl(IPC_SET), semctl(IPC_SET) and
> shmctl(IPC_SET) behave.
> 
> When "LONG1 1" is echoed to this file, xxxctl(IPC_SET) will set the time
> fields and the pid fields according to what is specified in the input
> parameter (while currently only the permission fields are allowed to be set).
> The following syscalls are impacted:
> . msgctl(IPC_SET)
> . semctl(IPC_SET)
> . shmctl(IPC_SET)
> 
> This makes it easy to restart an ipc object exactly is it was during the
> checkpoint phase.
> 
> Signed-off-by: Nadia Derbey <Nadia.Derbey-6ktuUTfB/bM@public.gmane.org>

Acked-by: Serge Hallyn <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>

thanks,
-serge

> ---
>  include/linux/next_syscall_data.h |   12 ++++++++++++
>  ipc/msg.c                         |   19 ++++++++++++++++++-
>  ipc/sem.c                         |   16 +++++++++++++++-
>  ipc/shm.c                         |   19 ++++++++++++++++++-
>  4 files changed, 63 insertions(+), 3 deletions(-)
> 
> Index: linux-2.6.26-rc8-mm1/include/linux/next_syscall_data.h
> ===================================================================
> --- linux-2.6.26-rc8-mm1.orig/include/linux/next_syscall_data.h	2008-07-08 12:22:47.000000000 +0200
> +++ linux-2.6.26-rc8-mm1/include/linux/next_syscall_data.h	2008-07-08 12:24:29.000000000 +0200
> @@ -6,6 +6,7 @@
>   *    . object creation with a predefined id
>   *         . for a sysv ipc object
>   *         . for a process
> + *    . set more than the usual ipc_perm fields during and IPC_SET operation.
>   */
> 
>  #ifndef _LINUX_NEXT_SYSCALL_DATA_H
> @@ -20,6 +21,10 @@
>   * by next syscall. The following syscalls support this feature:
>   *    . msgget(), semget(), shmget()
>   *    . fork(), vfork(), clone()
> + *
> + * If it is set to a non null value before a call to:
> + *    . msgctl(IPC_SET), semctl(IPC_SET), shmctl(IPC_SET),
> + * this means that we are going to set more than the usual ipc_perms fields.
>   */
>  struct next_syscall_data {
>  	int ndata;
> @@ -35,6 +40,13 @@ struct next_syscall_data {
> 
>  #define get_next_data(tsk)	((tsk)->nsd->data[0])
> 
> +/*
> + * Returns true if next call to xxxctl(IPC_SET) should have a non-default
> + * behavior.
> + */
> +#define ipc_set_all(tsk)	(next_data_set(tsk) ? get_next_data(tsk) : 0)
> +
> +
>  extern ssize_t get_next_syscall_data(struct task_struct *, char *, size_t);
>  extern int set_next_syscall_data(struct task_struct *, char *);
>  extern void reset_next_syscall_data(struct task_struct *);
> Index: linux-2.6.26-rc8-mm1/ipc/msg.c
> ===================================================================
> --- linux-2.6.26-rc8-mm1.orig/ipc/msg.c	2008-07-08 12:12:36.000000000 +0200
> +++ linux-2.6.26-rc8-mm1/ipc/msg.c	2008-07-08 12:26:03.000000000 +0200
> @@ -446,7 +446,24 @@ static int msgctl_down(struct ipc_namesp
>  		msq->q_qbytes = msqid64.msg_qbytes;
> 
>  		ipc_update_perm(&msqid64.msg_perm, ipcp);
> -		msq->q_ctime = get_seconds();
> +		if (unlikely(ipc_set_all(current))) {
> +			/*
> +			 * If this field is set in the task struct, this
> +			 * means that we want to set more than the usual
> +			 * fields. Particularly useful to restart a msgq
> +			 * in the same state as it was before being
> +			 * checkpointed.
> +			 */
> +			msq->q_stime = msqid64.msg_stime;
> +			msq->q_rtime = msqid64.msg_rtime;
> +			msq->q_ctime = msqid64.msg_ctime;
> +			msq->q_lspid = msqid64.msg_lspid;
> +			msq->q_lrpid = msqid64.msg_lrpid;
> +
> +			reset_next_syscall_data(current);
> +		} else
> +			msq->q_ctime = get_seconds();
> +
>  		/* sleeping receivers might be excluded by
>  		 * stricter permissions.
>  		 */
> Index: linux-2.6.26-rc8-mm1/ipc/sem.c
> ===================================================================
> --- linux-2.6.26-rc8-mm1.orig/ipc/sem.c	2008-07-08 12:12:36.000000000 +0200
> +++ linux-2.6.26-rc8-mm1/ipc/sem.c	2008-07-08 12:27:06.000000000 +0200
> @@ -874,7 +874,21 @@ static int semctl_down(struct ipc_namesp
>  		goto out_up;
>  	case IPC_SET:
>  		ipc_update_perm(&semid64.sem_perm, ipcp);
> -		sma->sem_ctime = get_seconds();
> +
> +		if (unlikely(ipc_set_all(current))) {
> +			/*
> +			 * If this field is set in the task struct, this
> +			 * means that we want to set more than the usual
> +			 * fields. Particularly useful to restart a semaphore
> +			 * in the same state as it was before being
> +			 * checkpointed.
> +			 */
> +			sma->sem_ctime = semid64.sem_ctime;
> +			sma->sem_otime = semid64.sem_otime;
> +
> +			reset_next_syscall_data(current);
> +		} else
> +			sma->sem_ctime = get_seconds();
>  		break;
>  	default:
>  		err = -EINVAL;
> Index: linux-2.6.26-rc8-mm1/ipc/shm.c
> ===================================================================
> --- linux-2.6.26-rc8-mm1.orig/ipc/shm.c	2008-07-08 12:12:36.000000000 +0200
> +++ linux-2.6.26-rc8-mm1/ipc/shm.c	2008-07-08 12:27:32.000000000 +0200
> @@ -609,7 +609,24 @@ static int shmctl_down(struct ipc_namesp
>  		goto out_up;
>  	case IPC_SET:
>  		ipc_update_perm(&shmid64.shm_perm, ipcp);
> -		shp->shm_ctim = get_seconds();
> +
> +		if (unlikely(ipc_set_all(current))) {
> +			/*
> +			 * If this field is set in the task struct, this
> +			 * means that we want to set more than the usual
> +			 * fields. Particularly useful to restart a shm seg
> +			 * in the same state as it was before being
> +			 * checkpointed.
> +			 */
> +			shp->shm_atim = shmid64.shm_atime;
> +			shp->shm_dtim = shmid64.shm_dtime;
> +			shp->shm_ctim = shmid64.shm_ctime;
> +			shp->shm_cprid = shmid64.shm_cpid;
> +			shp->shm_lprid = shmid64.shm_lpid;
> +
> +			reset_next_syscall_data(current);
> +		} else
> +			shp->shm_ctim = get_seconds();
>  		break;
>  	default:
>  		err = -EINVAL;
> 
> --