Re: [PATCH] [RFC] c/r: Add UTS support (v2)

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

Quoting Dan Smith (danms-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org):
> This patch adds a "phase" of checkpoint that saves out information about any
> namespaces the task(s) may have.  Do this by tracking the nsproxy of the
> first task and making sure that the tasks that follow get hooked back to
> share the same one on restart.
> 
> Restart is handled in userspace by reading the UTS record(s), calling
> unshare() and setting the hostname accordingly.  See my changes to
> mktree.c for details.
> 
> I tested this with single and multiple task restore, on top of Oren's
> v13 tree.

Yeah this actually looks good to me.  

Someone might complain about the per-task namespace data not showing
up in the per-task data, but I think the way you have it simplifies
things enough to justify it.

Do add a note to Documentation/checkpoint/internals.txt (and maybe
use __NEW_UTS_LEN+1 instead of 65), but other than that it looks
good to me.

thanks,
-serge

> Changes:
>   - Remove the kernel restore path
>   - Punt on nested namespaces
> 
> Signed-off-by: Dan Smith <danms-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
> ---
>  checkpoint/checkpoint.c        |   80 ++++++++++++++++++++++++++++++++++++++++
>  checkpoint/objhash.c           |    7 +++
>  checkpoint/restart.c           |    1 +
>  include/linux/checkpoint.h     |    1 +
>  include/linux/checkpoint_hdr.h |   15 +++++++
>  5 files changed, 104 insertions(+), 0 deletions(-)
> 
> diff --git a/checkpoint/checkpoint.c b/checkpoint/checkpoint.c
> index 64155de..12eb1d5 100644
> --- a/checkpoint/checkpoint.c
> +++ b/checkpoint/checkpoint.c
> @@ -193,6 +193,82 @@ static int cr_write_tail(struct cr_ctx *ctx)
>  	return ret;
>  }
> 
> +static int cr_write_ns_uts(struct cr_ctx *ctx, struct task_struct *t)
> +{
> +	struct cr_hdr h;
> +	struct cr_hdr_utsns *hh = cr_hbuf_get(ctx, sizeof(*hh));
> +	struct new_utsname *n = &t->nsproxy->uts_ns->name;
> +	int ret;
> +
> +	h.type = CR_HDR_UTSNS;
> +	h.len = sizeof(*hh);
> +	h.parent = 0;
> +
> +	memcpy(hh->nodename, n->nodename, sizeof(n->nodename));
> +	memcpy(hh->domainname, n->domainname, sizeof(n->domainname));
> +
> +	ret = cr_write_obj(ctx, &h, hh);
> +	cr_hbuf_put(ctx, sizeof(*hh));
> +
> +	return ret;
> +}
> +
> +static int cr_write_namespaces(struct cr_ctx *ctx, struct task_struct *t)
> +{
> +	struct cr_hdr h;
> +	struct cr_hdr_nsproxy *hh = cr_hbuf_get(ctx, sizeof(*hh));
> +	struct nsproxy *nsp = t->nsproxy;
> +	int ret;
> +	int new;
> +
> +	if (nsp != ctx->root_nsproxy) {
> +		/* Don't allow checkpoint of nested namespaces yet */
> +		pr_debug("Task has different nsproxy than root\n");
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +
> +	h.type = CR_HDR_NSP;
> +	h.len = sizeof(*hh);
> +	h.parent = 0;
> +
> +	new = cr_obj_add_ptr(ctx, nsp, &hh->objref, CR_OBJ_NSP, 0);
> +	if (new)
> +		hh->types = CR_NSP_UTS; /* Record types we support */
> +	else
> +		hh->types = 0;
> +
> +	ret = cr_write_obj(ctx, &h, hh);
> +	if (ret)
> +		goto out;
> +
> +	if (new) {
> +		ret = cr_write_ns_uts(ctx, t);
> +		if (ret < 0)
> +			goto out;
> +
> +		/* FIXME: Write other namespaces here */
> +	}
> + out:
> +	cr_hbuf_put(ctx, sizeof(*hh));
> +
> +	return ret;
> +}
> +
> +static int cr_write_all_namespaces(struct cr_ctx *ctx)
> +{
> +	int n, ret = 0;
> +
> +	for (n = 0; n < ctx->tasks_nr; n++) {
> +		pr_debug("dumping ns for task #%d\n", n);
> +		ret = cr_write_namespaces(ctx, ctx->tasks_arr[n]);
> +		if (ret < 0)
> +			break;
> +	}
> +
> +	return ret;
> +}
> +
>  /* dump the task_struct of a given task */
>  static int cr_write_task_struct(struct cr_ctx *ctx, struct task_struct *t)
>  {
> @@ -549,6 +625,10 @@ int do_checkpoint(struct cr_ctx *ctx, pid_t pid)
>  	if (ret < 0)
>  		goto out;
> 
> +	ret = cr_write_all_namespaces(ctx);
> +	if (ret < 0)
> +		goto out;
> +
>  	ret = cr_write_all_tasks(ctx);
>  	if (ret < 0)
>  		goto out;
> diff --git a/checkpoint/objhash.c b/checkpoint/objhash.c
> index ee31b38..aaaf583 100644
> --- a/checkpoint/objhash.c
> +++ b/checkpoint/objhash.c
> @@ -12,6 +12,7 @@
>  #include <linux/file.h>
>  #include <linux/hash.h>
>  #include <linux/checkpoint.h>
> +#include <linux/utsname.h>
> 
>  struct cr_objref {
>  	int objref;
> @@ -35,6 +36,9 @@ static void cr_obj_ref_drop(struct cr_objref *obj)
>  	case CR_OBJ_FILE:
>  		fput((struct file *) obj->ptr);
>  		break;
> +	case CR_OBJ_NSP:
> +		put_nsproxy((struct nsproxy *) obj->ptr);
> +		break;
>  	default:
>  		BUG();
>  	}
> @@ -46,6 +50,9 @@ static void cr_obj_ref_grab(struct cr_objref *obj)
>  	case CR_OBJ_FILE:
>  		get_file((struct file *) obj->ptr);
>  		break;
> +	case CR_OBJ_NSP:
> +		get_nsproxy((struct nsproxy *) obj->ptr);
> +		break;
>  	default:
>  		BUG();
>  	}
> diff --git a/checkpoint/restart.c b/checkpoint/restart.c
> index 7ec4de4..0ed01aa 100644
> --- a/checkpoint/restart.c
> +++ b/checkpoint/restart.c
> @@ -15,6 +15,7 @@
>  #include <linux/magic.h>
>  #include <linux/checkpoint.h>
>  #include <linux/checkpoint_hdr.h>
> +#include <linux/utsname.h>
> 
>  #include "checkpoint_arch.h"
> 
> diff --git a/include/linux/checkpoint.h b/include/linux/checkpoint.h
> index 217cf6e..5966275 100644
> --- a/include/linux/checkpoint.h
> +++ b/include/linux/checkpoint.h
> @@ -75,6 +75,7 @@ extern void cr_ctx_put(struct cr_ctx *ctx);
> 
>  enum {
>  	CR_OBJ_FILE = 1,
> +	CR_OBJ_NSP,
>  	CR_OBJ_MAX
>  };
> 
> diff --git a/include/linux/checkpoint_hdr.h b/include/linux/checkpoint_hdr.h
> index 6dc739f..1413572 100644
> --- a/include/linux/checkpoint_hdr.h
> +++ b/include/linux/checkpoint_hdr.h
> @@ -49,6 +49,8 @@ enum {
>  	CR_HDR_TASK,
>  	CR_HDR_THREAD,
>  	CR_HDR_CPU,
> +	CR_HDR_NSP,
> +	CR_HDR_UTSNS,
> 
>  	CR_HDR_MM = 201,
>  	CR_HDR_VMA,
> @@ -156,4 +158,17 @@ struct cr_hdr_fd_data {
>  	__u64 f_version;
>  } __attribute__((aligned(8)));
> 
> +#define CR_NSP_UTS 1
> +
> +struct cr_hdr_nsproxy {
> +	__u32 objref;
> +	__u32 types;
> +};
> +
> +struct cr_hdr_utsns {
> +	/* Both of these fields are defined as 65-chars long */
> +	char nodename[65];
> +	char domainname[65];
> +};
> +
>  #endif /* _CHECKPOINT_CKPT_HDR_H_ */
> -- 
> 1.5.6.3
> 
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