[Devel] Re: [PATCH 4/9] Introduce container dump function

[Serge E. Hallyn]

Quoting Andrey Mirkin (major at openvz.org):
> Actually right now we are going to dump only one process.
> Function for dumping head of image file are added.
> 
> Signed-off-by: Andrey Mirkin <major at openvz.org>
> ---
>  cpt/Makefile     |    2 +-
>  cpt/checkpoint.c |   74 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  cpt/cpt.h        |    3 ++
>  cpt/sys.c        |    3 +-
>  kernel/fork.c    |    2 +
>  5 files changed, 82 insertions(+), 2 deletions(-)
>  create mode 100644 cpt/checkpoint.c
> 
> diff --git a/cpt/Makefile b/cpt/Makefile
> index bfe75d5..173346b 100644
> --- a/cpt/Makefile
> +++ b/cpt/Makefile
> @@ -2,4 +2,4 @@ obj-y += sys_core.o
> 
>  obj-$(CONFIG_CHECKPOINT) += cptrst.o
> 
> -cptrst-objs := sys.o
> +cptrst-objs := sys.o checkpoint.o
> diff --git a/cpt/checkpoint.c b/cpt/checkpoint.c
> new file mode 100644
> index 0000000..b4d9686
> --- /dev/null
> +++ b/cpt/checkpoint.c
> @@ -0,0 +1,74 @@
> +/*
> + *  Copyright (C) 2008 Parallels, Inc.
> + *
> + *  Author: Andrey Mirkin <major at openvz.org>
> + *
> + *  This program is free software; you can redistribute it and/or
> + *  modify it under the terms of the GNU General Public License as
> + *  published by the Free Software Foundation, version 2 of the
> + *  License.
> + *
> + */
> +
> +#include <linux/sched.h>
> +#include <linux/fs.h>
> +#include <linux/file.h>
> +#include <linux/version.h>
> +
> +#include "cpt.h"
> +
> +static int cpt_write_head(struct cpt_context *ctx)
> +{
> +	struct cpt_head hdr;
> +
> +	memset(&hdr, 0, sizeof(hdr));
> +	hdr.cpt_signature[0] = CPT_SIGNATURE0;
> +	hdr.cpt_signature[1] = CPT_SIGNATURE1;
> +	hdr.cpt_signature[2] = CPT_SIGNATURE2;
> +	hdr.cpt_signature[3] = CPT_SIGNATURE3;
> +	hdr.cpt_hdrlen = sizeof(hdr);
> +	hdr.cpt_image_major = (LINUX_VERSION_CODE >> 16) & 0xff;
> +	hdr.cpt_image_minor = (LINUX_VERSION_CODE >> 8) & 0xff;
> +	hdr.cpt_image_sublevel = (LINUX_VERSION_CODE) & 0xff;
> +	hdr.cpt_image_extra = 0;
> +#if defined(CONFIG_X86_32)
> +	hdr.cpt_arch = CPT_ARCH_I386;
> +#else
> +#error  Arch is not supported
> +#endif
> +	return ctx->write(&hdr, sizeof(hdr), ctx);
> +}
> +
> +int dump_container(struct cpt_context *ctx)
> +{
> +	int err;
> +	struct task_struct *root;
> +
> +	read_lock(&tasklist_lock);
> +	root = find_task_by_vpid(ctx->pid);
> +	if (root)
> +		get_task_struct(root);
> +	read_unlock(&tasklist_lock);
> +
> +	err = -ESRCH;
> +	if (!root) {
> +		eprintk("can not find root task\n");
> +		return err;
> +	}
> +	ctx->nsproxy = root->nsproxy;
> +	if (!ctx->nsproxy) {
> +		eprintk("nsproxy is null\n");
> +		goto out;
> +	}

The get_task_struct() above won't pin the tsk->nsproxy
though, will it?  So should you be doing a
	rcu_read_lock();
	nsproxy = get_task_nsproxy(root);
	rcu_read_unlock();
to make sure the nsproxy doesn't disappear out from under
you?

(Maybe you do it in a later patch...)

thanks,
-serge

> +	err = cpt_write_head(ctx);
> +	
> +	/* Dump task here */
> +	if (!err)
> +		err = -ENOSYS;	
> +
> +out:
> +	ctx->nsproxy = NULL;
> +	put_task_struct(root);
> +	return err;
> +}
> diff --git a/cpt/cpt.h b/cpt/cpt.h
> index 607ac1b..b421a11 100644
> --- a/cpt/cpt.h
> +++ b/cpt/cpt.h
> @@ -33,6 +33,7 @@ typedef struct cpt_context
>  	int		refcount;
>  	int		ctx_state;
>  	struct semaphore main_sem;
> +	struct nsproxy	*nsproxy;
> 
>  	int		errno;
> 
> @@ -54,3 +55,5 @@ extern int debug_level;
> 
>  #define eprintk(a...) cpt_printk(1, "CPT ERR: " a)
>  #define dprintk(a...) cpt_printk(1, "CPT DBG: " a)
> +
> +int dump_container(struct cpt_context *ctx);
> diff --git a/cpt/sys.c b/cpt/sys.c
> index 8334c4c..6801c22 100644
> --- a/cpt/sys.c
> +++ b/cpt/sys.c
> @@ -109,9 +109,10 @@ static int checkpoint(pid_t pid, int fd, unsigned long flags)
> 
>  	ctx->file = file;
>  	ctx->ctx_state = CPT_CTX_DUMPING;
> +	ctx->pid = pid;
> 
>  	/* checkpoint */
> -	err = -ENOSYS;
> +	err = dump_container(ctx);
> 
>  	context_put(ctx);
> 
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 52b5037..f38b43d 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -77,6 +77,7 @@ int max_threads;		/* tunable limit on nr_threads */
>  DEFINE_PER_CPU(unsigned long, process_counts) = 0;
> 
>  __cacheline_aligned DEFINE_RWLOCK(tasklist_lock);  /* outer */
> +EXPORT_SYMBOL(tasklist_lock);
> 
>  int nr_processes(void)
>  {
> @@ -153,6 +154,7 @@ void __put_task_struct(struct task_struct *tsk)
>  	if (!profile_handoff_task(tsk))
>  		free_task(tsk);
>  }
> +EXPORT_SYMBOL(__put_task_struct);
> 
>  /*
>   * macro override instead of weak attribute alias, to workaround
> -- 
> 1.5.6
> 
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