Serge E. Hallyn wrote:
> Quoting Pavel Emelyanov ([EMAIL PROTECTED]):
>> Serge E. Hallyn wrote:
>>> Quoting Pavel Emelyanov ([EMAIL PROTECTED]):
>>>> [EMAIL PROTECTED] wrote:
>>>>> From: Sukadev Bhattiprolu <[EMAIL PROTECTED]>
>>>>> Subject: [RFC][PATCH 4/4]: Enable cloning PTY namespaces
>>>>>
>>>>> Enable cloning PTY namespaces.
>>>>>
>>>>> TODO:
>>>>> This version temporarily uses the clone flag '0x80000000' which
>>>>> is unused in mainline atm, but used for CLONE_IO in -mm.
>>>>> While we must extend clone() (urgently) to solve this, it hopefully
>>>>> does not affect review of the rest of this patchset.
>>>>>
>>>>> Changelog:
>>>>> - Version 0: Based on earlier versions from Serge Hallyn and
>>>>> Matt Helsley.
>>>>>
>>>>> Signed-off-by: Sukadev Bhattiprolu <[EMAIL PROTECTED]>
>>>>> ---
>>>>> fs/devpts/inode.c | 84
>>>>> +++++++++++++++++++++++++++++++++++++++-------
>>>>> include/linux/devpts_fs.h | 52 ++++++++++++++++++++++++++++
>>>>> include/linux/init_task.h | 1
>>>>> include/linux/nsproxy.h | 2 +
>>>>> include/linux/sched.h | 2 +
>>>>> kernel/fork.c | 2 -
>>>>> kernel/nsproxy.c | 17 ++++++++-
>>>>> 7 files changed, 146 insertions(+), 14 deletions(-)
>>>>>
>>>>> Index: linux-2.6.24/fs/devpts/inode.c
>>>>> ===================================================================
>>>>> --- linux-2.6.24.orig/fs/devpts/inode.c 2008-02-05 19:16:39.000000000
>>>>> -0800
>>>>> +++ linux-2.6.24/fs/devpts/inode.c 2008-02-05 20:27:41.000000000
>>>>> -0800
>>>>> @@ -25,18 +25,25 @@
>>>>> #define DEVPTS_SUPER_MAGIC 0x1cd1
>>>>>
>>>>> extern int pty_limit; /* Config limit on Unix98 ptys */
>>>>> -static DEFINE_IDR(allocated_ptys);
>>>>> static DECLARE_MUTEX(allocated_ptys_lock);
>>>>> +static struct file_system_type devpts_fs_type;
>>>>> +
>>>>> +struct pts_namespace init_pts_ns = {
>>>>> + .kref = {
>>>>> + .refcount = ATOMIC_INIT(2),
>>>>> + },
>>>>> + .allocated_ptys = IDR_INIT(init_pts_ns.allocated_ptys),
>>>>> + .mnt = NULL,
>>>>> +};
>>>>>
>>>>> static inline struct idr *current_pts_ns_allocated_ptys(void)
>>>>> {
>>>>> - return &allocated_ptys;
>>>>> + return ¤t->nsproxy->pts_ns->allocated_ptys;
>>>>> }
>>>>>
>>>>> -static struct vfsmount *devpts_mnt;
>>>>> static inline struct vfsmount *current_pts_ns_mnt(void)
>>>>> {
>>>>> - return devpts_mnt;
>>>>> + return current->nsproxy->pts_ns->mnt;
>>>>> }
>>>>>
>>>>> static struct {
>>>>> @@ -59,6 +66,42 @@ static match_table_t tokens = {
>>>>> {Opt_err, NULL}
>>>>> };
>>>>>
>>>>> +struct pts_namespace *new_pts_ns(void)
>>>>> +{
>>>>> + struct pts_namespace *ns;
>>>>> +
>>>>> + ns = kmalloc(sizeof(*ns), GFP_KERNEL);
>>>>> + if (!ns)
>>>>> + return ERR_PTR(-ENOMEM);
>>>>> +
>>>>> + ns->mnt = kern_mount_data(&devpts_fs_type, ns);
>>>> You create a circular references here - the namespace
>>>> holds the vfsmnt, the vfsmnt holds a superblock, a superblock
>>>> holds the namespace.
>>> Hmm, yeah, good point. That was probably in my original version last
>>> year, so my fault not Suka's. Suka, would it work to have the
>>> sb->s_info point to the namespace but not grab a reference, than have
>> If you don't then you may be in situation, when this devpts
>> is mounted from userspace and in case the namespace is dead
>> superblock will point to garbage... Superblock MUST hold the
>> namespace :)
>
> But when the ns is freed sb->s_info would be NULL. Surely the helpers
> can be made to handle that safely?
Hm... How do we find the proper superblock? Have a reference on
it from the namespace? I'm afraid it will be easy to resolve the
locking issues here.
I propose another scheme - we simply don't have ANY references
from namespace to superblock/vfsmount, but get the current
namespace in devpts_get_sb() and put in devpts_free_sb().
>>> free_pts_ns() null out its sb->s_info, i.e. something like
>>>
>>> void free_pts_ns(struct kref *ns_kref)
>>> {
>>> struct pts_namespace *ns;
>>> struct super_block *sb;
>>>
>>> ns = container_of(ns_kref, struct pts_namespace, kref);
>>> BUG_ON(ns == &init_pts_ns);
>>> sb = ns->mnt->mnt_sb;
>>>
>>> mntput(ns->mnt);
>>> sb->s_info = NULL;
>>>
>>> /*
>>> * TODO:
>>> * idr_remove_all(&ns->allocated_ptys); introduced in
>>> .6.23
>>> */
>>> idr_destroy(&ns->allocated_ptys);
>>> kfree(ns);
>>> }
>>>
>>>
>
_______________________________________________
Containers mailing list
[EMAIL PROTECTED]
https://lists.linux-foundation.org/mailman/listinfo/containers
_______________________________________________
Devel mailing list
[email protected]
https://openvz.org/mailman/listinfo/devel
