[Devel] Re: [PATCH] An attempt to have an unlimitedly extendable sys_clone
Pavel Emelyanov
xemul at openvz.org
Tue Jan 15 23:37:16 PST 2008
Oren Laadan wrote:
>
> 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.
>
> how about "CLONE_EXTEND" ?
I don't mind. The names I selected are not perfect. Better
ones are always welcome.
>> 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;
>> };
>
> how about "ext_clone_arg" ?
>
> (both suggestion make the use more explicit and are more
> consistent with each other; but definitely a nit ...)
"Extended" sounds good, thanks.
>> 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.
>
> Since the same kernel version (maj/min) can be compiled with
> different config options, need to ensure that not only are
> args added at the end, but also without #if/#ifdef around
> them.
Sure, but since this struct is declared outside the
#ifdef __KERNEL__ then the internal ifdefs will look
strange. But I will mention this in comment.
> That also means, that if a feature isn't compile (but the
> size argument remains larger because of fields required for
> other arguments, a user program currently has no way to
> figure out what's available and supported by the kernel.
> (see also comment below about the code).
>
>> Sure, we lose the ability to clone tasks with extended
>> argument and the CLONE_CHILD_SETTID/CLEARTID, but do we
>> really need this?
>
> not necessarily. the relevant field can be added (even
> already now) inside long_clone_arg, e.g. child_tidptr;
> so if the extra bit is set, _and_ ....CLEARTID is set,
> the pointer is found inside the extra struct.
>
> in other words we don't give up the functionality.
>
>> 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.
>>
>> Signed-off-by: Pavel Emelyanov <xemul at openzv.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);
>
> what about:
> if (size < sizeof(int))
> return ERR_PTR(-EINVAL);
Hm... Makes sense.
> I wonder how a caller could figure out what _is_ supported by the
> kernel on which it is running - that is, what is the "perfect" value
> for the "size" field (and whether that is necessary ?)
> For instance, the kernel could "put_user(sizeof(...), child_tidptr)"
> if the original size given by the caller is 0.
You mean use the clone to get what the kernel support? I don't
think this is good.
What would the program need to find out what the kernel support
at run-time? If we want to create some extra namespace and the
kernel returns -EINVAL then there's no need to restart the syscall
w/o asking it to clone this namespace. I think that once user
needs some namespace it finds out which kernel version he needs
and goes on.
>> +
>> + 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;
>
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