Re: [PATCH] An attempt to have an unlimitedly extendable sys_clone

[Cedric Le Goater <clg-NmTC/0ZBporQT0dZR+AlfA@public.gmane.org>]

Pavel Emelyanov wrote:
> We have one bit in the clone_flags left, so we won't be
> able to create more namespaces after we make it busy.
> Besides, for checkpoint/restart jobs we might want to
> create tasks with pre-defined pids (virtual of course).
> What else might be required from clone() - nobody knows.
> 
> This is an attempt to create a extendable API for clone.
> 
> I use the last bit in the clone_flags for CLONE_NEWCLONE.
> When set it will denote that the child_tidptr is not a
> pointer on the tid storage, but the pointer on the struct
> long_clone_struct which currently looks like this:
> 
> struct long_clone_arg {
> 	int size;
> };
> 
> When we want to add a new argument for clone we just put
> it *at the end of this structure* and adjust the size.
> The binary compatibility with older long_clone_arg-s is
> facilitated with the clone_arg_has() macro.

hmm, I wonder how lkml@ will react to this. do we have 
similar apis in the kernel ?

> Sure, we lose the ability to clone tasks with extended
> argument and the CLONE_CHILD_SETTID/CLEARTID, but do we
> really need this?

not in the extended clone flag version. I think.

> The same thing is about to be done for unshare - we can
> add the second argument for it and iff the CLONE_NEWCLONE
> is specified - try to use it. Binary compatibility with
> the old ushare will be kept.
>
> The new argument is pulled up to the create_new_namespaces
> so that later we can easily use it w/o sending additional
> patches.
> 
> This is a final, but a pre-review patch for sys_clone()
> that I plan to send to Andrew before we go on developing
> new namespaces.
> 
> Made against 2.6.24-rc5-mm1.

The patch looks good and I compiled it and booted on x64 and 
x86_64. 

I think we should add the unshare support before sending to
andrew and also add an extended flag array to show how it will 
be used. I have a mq_namespace patchset pending we could use
for that and send all together ?

C.

> Signed-off-by: Pavel Emelyanov <xemul-C3wRU7vazMYdnm+yROfE0A@public.gmane.org>
> 
> ---
> 
> diff --git a/include/linux/nsproxy.h b/include/linux/nsproxy.h
> index 0e66b57..e01de56 100644
> --- a/include/linux/nsproxy.h
> +++ b/include/linux/nsproxy.h
> @@ -62,7 +62,8 @@ static inline struct nsproxy *task_nsproxy(struct task_struct *tsk)
>  	return rcu_dereference(tsk->nsproxy);
>  }
> 
> -int copy_namespaces(unsigned long flags, struct task_struct *tsk);
> +int copy_namespaces(unsigned long flags, struct task_struct *tsk,
> +		struct long_clone_arg *carg);
>  void exit_task_namespaces(struct task_struct *tsk);
>  void switch_task_namespaces(struct task_struct *tsk, struct nsproxy *new);
>  void free_nsproxy(struct nsproxy *ns);
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index e4d2a82..585a2b4 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -27,6 +27,23 @@
>  #define CLONE_NEWUSER		0x10000000	/* New user namespace */
>  #define CLONE_NEWPID		0x20000000	/* New pid namespace */
>  #define CLONE_NEWNET		0x40000000	/* New network namespace */
> +#define CLONE_NEWCLONE		0x80000000	/* Has an long_clone_arg */
> +
> +/*
> + * If the CLONE_NEWCLONE argument is specified, then the
> + * child_tidptr is expected to point to the struct long_clone_arg.
> + *
> + * This structure has a variable size, which is to be recorded
> + * in the size member. All other members a to be put after this.
> + * Never ... No. Always add new members only at its tail.
> + *
> + * The clone_arg_has() macro is responsible for checking whether
> + * the given arg has the desired member.
> + */
> +
> +struct long_clone_arg {
> +	int size;
> +};
> 
>  /*
>   * Scheduling policies
> @@ -40,6 +57,11 @@
> 
>  #ifdef __KERNEL__
> 
> +#define clone_arg_has(arg, member)	({ \
> +		struct long_clone_arg *__carg = arg; \
> +		(__carg->size >= offsetof(struct long_clone_arg, member) + \
> +		 			sizeof(__carg->member)); })
> +
>  struct sched_param {
>  	int sched_priority;
>  };
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 8b558b7..f5895fc 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -967,6 +967,29 @@ static void rt_mutex_init_task(struct task_struct *p)
>  #endif
>  }
> 
> +static struct long_clone_arg *get_long_clone_arg(int __user *child_tidptr)
> +{
> +	int size;
> +	struct long_clone_arg *carg;
> +
> +	if (get_user(size, child_tidptr))
> +		return ERR_PTR(-EFAULT);
> +
> +	if (size > sizeof(struct long_clone_arg))
> +		return ERR_PTR(-EINVAL);
> +
> +	carg = kzalloc(sizeof(struct long_clone_arg), GFP_KERNEL);
> +	if (carg == NULL)
> +		return ERR_PTR(-ENOMEM);
> +
> +	if (copy_from_user(carg, child_tidptr, size)) {
> +		kfree(carg);
> +		return ERR_PTR(-EFAULT);
> +	}
> +
> +	return carg;
> +}
> +
>  /*
>   * This creates a new process as a copy of the old one,
>   * but does not actually start it yet.
> @@ -985,6 +1008,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
>  	int retval;
>  	struct task_struct *p;
>  	int cgroup_callbacks_done = 0;
> +	struct long_clone_arg *carg = NULL;
> 
>  	if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
>  		return ERR_PTR(-EINVAL);
> @@ -1004,6 +1028,11 @@ static struct task_struct *copy_process(unsigned long clone_flags,
>  	if ((clone_flags & CLONE_SIGHAND) && !(clone_flags & CLONE_VM))
>  		return ERR_PTR(-EINVAL);
> 
> +	if ((clone_flags & CLONE_NEWCLONE) &&
> +			(clone_flags & (CLONE_CHILD_SETTID | 
> +					CLONE_CHILD_CLEARTID)))
> +		return ERR_PTR(-EINVAL);
> +
>  	retval = security_task_create(clone_flags);
>  	if (retval)
>  		goto fork_out;
> @@ -1132,8 +1161,15 @@ static struct task_struct *copy_process(unsigned long clone_flags,
>  	/* Perform scheduler related setup. Assign this task to a CPU. */
>  	sched_fork(p, clone_flags);
> 
> +	if (clone_flags & CLONE_NEWCLONE) {
> +		carg = get_long_clone_arg(child_tidptr);
> +		retval = PTR_ERR(carg);
> +		if (IS_ERR(carg))
> +			goto bad_fork_cleanup_policy;
> +	}
> +
>  	if ((retval = security_task_alloc(p)))
> -		goto bad_fork_cleanup_policy;
> +		goto bad_fork_cleanup_carg;
>  	if ((retval = audit_alloc(p)))
>  		goto bad_fork_cleanup_security;
>  	/* copy all the process information */
> @@ -1151,7 +1187,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
>  		goto bad_fork_cleanup_signal;
>  	if ((retval = copy_keys(clone_flags, p)))
>  		goto bad_fork_cleanup_mm;
> -	if ((retval = copy_namespaces(clone_flags, p)))
> +	if ((retval = copy_namespaces(clone_flags, p, carg)))
>  		goto bad_fork_cleanup_keys;
>  	retval = copy_thread(0, clone_flags, stack_start, stack_size, p, regs);
>  	if (retval)
> @@ -1345,6 +1381,8 @@ bad_fork_cleanup_audit:
>  	audit_free(p);
>  bad_fork_cleanup_security:
>  	security_task_free(p);
> +bad_fork_cleanup_carg:
> +	kfree(carg);
>  bad_fork_cleanup_policy:
>  #ifdef CONFIG_NUMA
>  	mpol_free(p->mempolicy);
> diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
> index f5d332c..b955196 100644
> --- a/kernel/nsproxy.c
> +++ b/kernel/nsproxy.c
> @@ -48,7 +48,8 @@ static inline struct nsproxy *clone_nsproxy(struct nsproxy *orig)
>   * leave it to the caller to do proper locking and attach it to task.
>   */
>  static struct nsproxy *create_new_namespaces(unsigned long flags,
> -			struct task_struct *tsk, struct fs_struct *new_fs)
> +			struct task_struct *tsk, struct fs_struct *new_fs,
> +			struct long_clone_arg *carg)
>  {
>  	struct nsproxy *new_nsp;
>  	int err;
> @@ -119,7 +120,8 @@ out_ns:
>   * called from clone.  This now handles copy for nsproxy and all
>   * namespaces therein.
>   */
> -int copy_namespaces(unsigned long flags, struct task_struct *tsk)
> +int copy_namespaces(unsigned long flags, struct task_struct *tsk,
> +		struct long_clone_arg *carg)
>  {
>  	struct nsproxy *old_ns = tsk->nsproxy;
>  	struct nsproxy *new_ns;
> @@ -131,7 +133,8 @@ int copy_namespaces(unsigned long flags, struct task_struct *tsk)
>  	get_nsproxy(old_ns);
> 
>  	if (!(flags & (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC |
> -				CLONE_NEWUSER | CLONE_NEWPID | CLONE_NEWNET)))
> +				CLONE_NEWUSER | CLONE_NEWPID | CLONE_NEWNET |
> +				CLONE_NEWCLONE)))
>  		return 0;
> 
>  	if (!capable(CAP_SYS_ADMIN)) {
> @@ -139,7 +142,7 @@ int copy_namespaces(unsigned long flags, struct task_struct *tsk)
>  		goto out;
>  	}
> 
> -	new_ns = create_new_namespaces(flags, tsk, tsk->fs);
> +	new_ns = create_new_namespaces(flags, tsk, tsk->fs, carg);
>  	if (IS_ERR(new_ns)) {
>  		err = PTR_ERR(new_ns);
>  		goto out;
> @@ -191,7 +194,7 @@ int unshare_nsproxy_namespaces(unsigned long unshare_flags,
>  		return -EPERM;
> 
>  	*new_nsp = create_new_namespaces(unshare_flags, current,
> -				new_fs ? new_fs : current->fs);
> +				new_fs ? new_fs : current->fs, NULL);
>  	if (IS_ERR(*new_nsp)) {
>  		err = PTR_ERR(*new_nsp);
>  		goto out;