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

Serge E. Hallyn
2008-09-03T14:23:22Z

Quoting Andrey Mirkin (major@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@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@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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