Re: How much of a mess does OpenVZ make? ;) Was: What can OpenVZ do?

From: Ying Han
Date: Fri Mar 13 2009 - 00:29:54 EST

Hi Serge:
I made a patch based on Oren's tree recently which implement a new
syscall clone_with_pid. I tested with checkpoint/restart process tree
and it works as expected.
This patch has some hack in it which i made a copy of libc's clone and
made modifications of passing one more argument(pid number). I will
try to clean up the code and do more testing.

New syscall clone_with_pid
Implement a new syscall which clone a thread with a preselected pid number.

clone_with_pid(child_func, child_stack + CHILD_STACK - 16,
CLONE_WITH_PID|SIGCHLD, pid, NULL);

Signed-off-by: Ying Han <yinghan@xxxxxxxxxx>

diff --git a/arch/x86/include/asm/syscalls.h b/arch/x86/include/asm/syscalls.h
index 87803da..b5a1b03 100644
--- a/arch/x86/include/asm/syscalls.h
+++ b/arch/x86/include/asm/syscalls.h
@@ -26,6 +26,7 @@ asmlinkage int sys_fork(struct pt_regs);
asmlinkage int sys_clone(struct pt_regs);
asmlinkage int sys_vfork(struct pt_regs);
asmlinkage int sys_execve(struct pt_regs);
+asmlinkage int sys_clone_with_pid(struct pt_regs);

/* kernel/signal_32.c */
asmlinkage int sys_sigsuspend(int, int, old_sigset_t);
diff --git a/arch/x86/include/asm/unistd_32.h b/arch/x86/include/asm/unistd_32
index a5f9e09..f10ca0e 100644
--- a/arch/x86/include/asm/unistd_32.h
+++ b/arch/x86/include/asm/unistd_32.h
@@ -340,6 +340,7 @@
#define __NR_inotify_init1 332
#define __NR_checkpoint 333
#define __NR_restart 334
+#define __NR_clone_with_pid 335

#ifdef __KERNEL__

diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index 0a1302f..88ae634 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -8,7 +8,6 @@
/*
* This file handles the architecture-dependent parts of process handling..
*/
-
#include <stdarg.h>

#include <linux/cpu.h>
@@ -652,6 +651,28 @@ asmlinkage int sys_clone(struct pt_regs regs)
return do_fork(clone_flags, newsp, &regs, 0, parent_tidptr, child_tidptr);
}

+/**
+ * sys_clone_with_pid - clone a thread with pre-select pid number.
+ */
+asmlinkage int sys_clone_with_pid(struct pt_regs regs)
+{
+ unsigned long clone_flags;
+ unsigned long newsp;
+ int __user *parent_tidptr, *child_tidptr;
+ pid_t pid_nr;
+
+ clone_flags = regs.bx;
+ newsp = regs.cx;
+ parent_tidptr = (int __user *)regs.dx;
+ child_tidptr = (int __user *)regs.di;
+ pid_nr = regs.bp;
+
+ if (!newsp)
+ newsp = regs.sp;
+ return do_fork(clone_flags, newsp, &regs, pid_nr, parent_tidptr,
+ child_tidptr);
+}
+
/*
* This is trivial, and on the face of it looks like it
* could equally well be done in user mode.
diff --git a/arch/x86/kernel/syscall_table_32.S b/arch/x86/kernel/syscall_tabl
index 5543136..5191117 100644
--- a/arch/x86/kernel/syscall_table_32.S
+++ b/arch/x86/kernel/syscall_table_32.S
@@ -334,3 +334,4 @@ ENTRY(sys_call_table)
.long sys_inotify_init1
.long sys_checkpoint
.long sys_restart
+ .long sys_clone_with_pid
diff --git a/arch/x86/mm/checkpoint.c b/arch/x86/mm/checkpoint.c
index 50bde9a..a4aee65 100644
--- a/arch/x86/mm/checkpoint.c
+++ b/arch/x86/mm/checkpoint.c
@@ -7,7 +7,6 @@
* License. See the file COPYING in the main directory of the Linux
* distribution for more details.
*/
-
#include <asm/desc.h>
#include <asm/i387.h>

diff --git a/checkpoint/checkpoint.c b/checkpoint/checkpoint.c
index 64155de..b7de611 100644
--- a/checkpoint/checkpoint.c
+++ b/checkpoint/checkpoint.c
@@ -8,6 +8,7 @@
* distribution for more details.
*/

+#define DEBUG
#include <linux/version.h>
#include <linux/sched.h>
#include <linux/ptrace.h>
@@ -564,3 +565,4 @@ int do_checkpoint(struct cr_ctx *ctx, pid_t pid)
out:
return ret;
}
+
diff --git a/checkpoint/ckpt_file.c b/checkpoint/ckpt_file.c
index e3097ac..a8c5ad5 100644
--- a/checkpoint/ckpt_file.c
+++ b/checkpoint/ckpt_file.c
@@ -7,7 +7,7 @@
* License. See the file COPYING in the main directory of the Linux
* distribution for more details.
*/
-
+#define DEBUG
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/file.h>
diff --git a/checkpoint/ckpt_mem.c b/checkpoint/ckpt_mem.c
index 4925ff2..ca5840b 100644
--- a/checkpoint/ckpt_mem.c
+++ b/checkpoint/ckpt_mem.c
@@ -7,7 +7,7 @@
* License. See the file COPYING in the main directory of the Linux
* distribution for more details.
*/
-
+#define DEBUG
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/slab.h>
diff --git a/checkpoint/restart.c b/checkpoint/restart.c
index 7ec4de4..30e43c2 100644
--- a/checkpoint/restart.c
+++ b/checkpoint/restart.c
@@ -8,6 +8,7 @@
* distribution for more details.
*/

+#define DEBUG
#include <linux/version.h>
#include <linux/sched.h>
#include <linux/wait.h>
@@ -242,7 +243,7 @@ static int cr_read_task_struct(struct cr_ctx *ctx)
memcpy(t->comm, buf, min(hh->task_comm_len, TASK_COMM_LEN));
}
kfree(buf);
-
+ pr_debug("read task %s\n", t->comm);
/* FIXME: restore remaining relevant task_struct fields */
out:
cr_hbuf_put(ctx, sizeof(*hh));
diff --git a/checkpoint/rstr_file.c b/checkpoint/rstr_file.c
index f44b081..755e40e 100644
--- a/checkpoint/rstr_file.c
+++ b/checkpoint/rstr_file.c
@@ -7,7 +7,7 @@
* License. See the file COPYING in the main directory of the Linux
* distribution for more details.
*/
-
+#define DEBUG
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/fs.h>
diff --git a/checkpoint/rstr_mem.c b/checkpoint/rstr_mem.c
index 4d5ce1a..8330468 100644
--- a/checkpoint/rstr_mem.c
+++ b/checkpoint/rstr_mem.c
@@ -7,7 +7,7 @@
* License. See the file COPYING in the main directory of the Linux
* distribution for more details.
*/
-
+#define DEBUG
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/fcntl.h>
diff --git a/checkpoint/sys.c b/checkpoint/sys.c
index f26b0c6..d1a5394 100644
--- a/checkpoint/sys.c
+++ b/checkpoint/sys.c
@@ -7,7 +7,7 @@
* License. See the file COPYING in the main directory of the Linux
* distribution for more details.
*/
-
+#define DEBUG
#include <linux/sched.h>
#include <linux/nsproxy.h>
#include <linux/kernel.h>
@@ -263,7 +263,6 @@ asmlinkage long sys_checkpoint(pid_t pid, int fd, unsigned
return PTR_ERR(ctx);

ret = do_checkpoint(ctx, pid);
-
if (!ret)
ret = ctx->crid;

@@ -304,3 +303,4 @@ asmlinkage long sys_restart(int crid, int fd, unsigned lon
cr_ctx_put(ctx);
return ret;
}
+
diff --git a/include/linux/checkpoint.h b/include/linux/checkpoint.h
index 217cf6e..bc2c202 100644
--- a/include/linux/checkpoint.h
+++ b/include/linux/checkpoint.h
@@ -114,7 +114,6 @@ extern int cr_write_files(struct cr_ctx *ctx, struct task_
extern int do_restart(struct cr_ctx *ctx, pid_t pid);
extern int cr_read_mm(struct cr_ctx *ctx);
extern int cr_read_files(struct cr_ctx *ctx);
-
#ifdef pr_fmt
#undef pr_fmt
#endif
diff --git a/include/linux/pid.h b/include/linux/pid.h
index d7e98ff..86e2f61 100644
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -119,7 +119,7 @@ extern struct pid *find_get_pid(int nr);
extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
int next_pidmap(struct pid_namespace *pid_ns, int last);

-extern struct pid *alloc_pid(struct pid_namespace *ns);
+extern struct pid *alloc_pid(struct pid_namespace *ns, pid_t pid_nr);
extern void free_pid(struct pid *pid);

/*
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 0150e90..7fb4e28 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -28,6 +28,7 @@
#define CLONE_NEWPID 0x20000000 /* New pid namespace */
#define CLONE_NEWNET 0x40000000 /* New network namespace */
#define CLONE_IO 0x80000000 /* Clone io context */
+#define CLONE_WITH_PID 0x00001000 /* Clone with pre-select PID */

/*
* Scheduling policies
diff --git a/kernel/exit.c b/kernel/exit.c
index 2d8be7e..4baf651 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -3,7 +3,7 @@
*
* Copyright (C) 1991, 1992 Linus Torvalds
*/
-
+#define DEBUG
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/interrupt.h>
@@ -1676,6 +1676,7 @@ static long do_wait(enum pid_type type, struct pid *pid,
DECLARE_WAITQUEUE(wait, current);
struct task_struct *tsk;
int retval;
+ int level;

trace_sched_process_wait(pid);

@@ -1708,7 +1709,6 @@ repeat:
retval = tsk_result;
goto end;
}
-
if (options & __WNOTHREAD)
break;
tsk = next_thread(tsk);
@@ -1817,7 +1817,6 @@ asmlinkage long sys_wait4(pid_t upid, int __user *stat_a
type = PIDTYPE_PID;
pid = find_get_pid(upid);
}
-
ret = do_wait(type, pid, options | WEXITED, NULL, stat_addr, ru);
put_pid(pid);

diff --git a/kernel/fork.c b/kernel/fork.c
index 085ce56..262ae1e 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -10,7 +10,7 @@
* Fork is rather simple, once you get the hang of it, but the memory
* management can be a bitch. See 'mm/memory.c': 'copy_page_range()'
*/
-
+#define DEBUG
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/unistd.h>
@@ -959,10 +959,19 @@ static struct task_struct *copy_process(unsigned long cl
int retval;
struct task_struct *p;
int cgroup_callbacks_done = 0;
+ pid_t clone_pid = stack_size;

if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
return ERR_PTR(-EINVAL);

+ /* We only allow the clone_with_pid when a new pid namespace is
+ * created. FIXME: how to restrict it.
+ */
+ if ((clone_flags & CLONE_NEWPID) && (clone_flags & CLONE_WITH_PID))
+ return ERR_PTR(-EINVAL);
+ if ((clone_flags & CLONE_WITH_PID) && (clone_pid <= 1))
+ return ERR_PTR(-EINVAL);
+
/*
* Thread groups must share signals as well, and detached threads
* can only be started up within the thread group.
@@ -1135,7 +1144,10 @@ static struct task_struct *copy_process(unsigned long c

if (pid != &init_struct_pid) {
retval = -ENOMEM;
- pid = alloc_pid(task_active_pid_ns(p));
+ if (clone_flags & CLONE_WITH_PID)
+ pid = alloc_pid(task_active_pid_ns(p), clone_pid);
+ else
+ pid = alloc_pid(task_active_pid_ns(p), 0);
if (!pid)
goto bad_fork_cleanup_io;

@@ -1162,6 +1174,8 @@ static struct task_struct *copy_process(unsigned long cl
* Clear TID on mm_release()?
*/
p->clear_child_tid = (clone_flags & CLONE_CHILD_CLEARTID) ? child_tidptr: NU
+
+
#ifdef CONFIG_FUTEX
p->robust_list = NULL;
#ifdef CONFIG_COMPAT
diff --git a/kernel/pid.c b/kernel/pid.c
index 064e76a..0facf05 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -25,7 +25,7 @@
* Many thanks to Oleg Nesterov for comments and help
*
*/
-
+#define DEBUG
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/slab.h>
@@ -122,12 +122,15 @@ static void free_pidmap(struct upid *upid)
atomic_inc(&map->nr_free);
}

-static int alloc_pidmap(struct pid_namespace *pid_ns)
+static int alloc_pidmap(struct pid_namespace *pid_ns, pid_t pid_nr)
{
int i, offset, max_scan, pid, last = pid_ns->last_pid;
struct pidmap *map;

- pid = last + 1;
+ if (pid_nr)
+ pid = pid_nr;
+ else
+ pid = last + 1;
if (pid >= pid_max)
pid = RESERVED_PIDS;
offset = pid & BITS_PER_PAGE_MASK;
@@ -153,9 +156,12 @@ static int alloc_pidmap(struct pid_namespace *pid_ns)
do {
if (!test_and_set_bit(offset, map->page)) {
atomic_dec(&map->nr_free);
- pid_ns->last_pid = pid;
+ if (!pid_nr)
+ pid_ns->last_pid = pid;
return pid;
}
+ if (pid_nr)
+ return -1;
offset = find_next_offset(map, offset);
pid = mk_pid(pid_ns, map, offset);
/*
@@ -239,21 +245,25 @@ void free_pid(struct pid *pid)
call_rcu(&pid->rcu, delayed_put_pid);
}

-struct pid *alloc_pid(struct pid_namespace *ns)
+struct pid *alloc_pid(struct pid_namespace *ns, pid_t pid_nr)
{
struct pid *pid;
enum pid_type type;
int i, nr;
struct pid_namespace *tmp;
struct upid *upid;
+ int level = ns->level;
+
+ if (pid_nr >= pid_max)
+ return NULL;

pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL);
if (!pid)
goto out;

- tmp = ns;
- for (i = ns->level; i >= 0; i--) {
- nr = alloc_pidmap(tmp);
+ tmp = ns->parent;
+ for (i = level-1; i >= 0; i--) {
+ nr = alloc_pidmap(tmp, 0);
if (nr < 0)
goto out_free;

@@ -262,6 +272,14 @@ struct pid *alloc_pid(struct pid_namespace *ns)
tmp = tmp->parent;
}

+ nr = alloc_pidmap(ns, pid_nr);
+ if (nr < 0)
+ goto out_free;
+ pid->numbers[level].nr = nr;
+ pid->numbers[level].ns = ns;
+ if (nr == pid_nr)
+ pr_debug("nr == pid_nr == %d\n", nr);
+
get_pid_ns(ns);
pid->level = ns->level;
atomic_set(&pid->count, 1);








On Thu, Mar 12, 2009 at 2:21 PM, Serge E. Hallyn <serue@xxxxxxxxxx> wrote:
>
> Quoting Greg Kurz (gkurz@xxxxxxxxxx):
> > On Thu, 2009-03-12 at 09:53 -0500, Serge E. Hallyn wrote:
> > > Or are you suggesting that you'll do a dummy clone of (5594,2) so that
> > > the next clone(CLONE_NEWPID) will be expected to be (5594,3,1)?
> > >
> >
> > Of course not
>
> Ok - someone *did* argue that at some point I think...
>
> > but one should be able to tell clone() to pick a specific
> > pid.
>
> Can you explain exactly how?  I must be missing something clever.
>
> -serge
>
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@xxxxxxxxxx  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/