[Devel] Re: [PATCH 1/9] Containers (V9): Basic container framework

[Balbir Singh]

menage at google.com wrote:
> This patch adds the main containers framework - the container
> filesystem, and the basic structures for tracking membership and
> associating subsystem state objects to tasks.

[snip]

> +*** notify_on_release is disabled in the current patch set. It may be
> +*** reactivated in a future patch in a less-intrusive manner
> +

Won't this break user space tools for cpusets?

[snip]

> +See kernel/container.c for more details.
> +
> +Subsystems can take/release the container_mutex via the functions
> +container_lock()/container_unlock(), and can
> +take/release the callback_mutex via the functions
> +container_lock()/container_unlock().
> +

Hmm.. looks like a documentation error. Both mutex's are obtained through
container_lock/container_unlock ?

> +Accessing a task's container pointer may be done in the following ways:
> +- while holding container_mutex
> +- while holding the task's alloc_lock (via task_lock())
> +- inside an rcu_read_lock() section via rcu_dereference()
> +

container_mutex() and task_lock() can be used for changing the pointer?
Could you please explain this a bit further.

[snip]

> +int populate(struct container_subsys *ss, struct container *cont)
> +LL=none
> +
> +Called after creation of a container to allow a subsystem to populate
> +the container directory with file entries.  The subsystem should make
> +calls to container_add_file() with objects of type cftype (see
> +include/linux/container.h for details).  Note that although this
> +method can return an error code, the error code is currently not
> +always handled well.

We needed the equivalent of container_remove_file() to be called
if container_add_file() failed.

[snip]


> +struct container {
> +	unsigned long flags;		/* "unsigned long" so bitops work */
> +
> +	/* count users of this container. >0 means busy, but doesn't
> +	 * necessarily indicate the number of tasks in the
> +	 * container */
> +	atomic_t count;
> +
> +	/*
> +	 * We link our 'sibling' struct into our parent's 'children'.
> +	 * Our children link their 'sibling' into our 'children'.
> +	 */
> +	struct list_head sibling;	/* my parent's children */
> +	struct list_head children;	/* my children */
> +
> +	struct container *parent;	/* my parent */
> +	struct dentry *dentry;	  	/* container fs entry */
> +
> +	/* Private pointers for each registered subsystem */
> +	struct container_subsys_state *subsys[CONTAINER_SUBSYS_COUNT];
> +
> +	struct containerfs_root *root;
> +	struct container *top_container;
> +};

Can't we derive the top_container from containerfs_root?

> +
> +/* struct cftype:
> + *
> + * The files in the container filesystem mostly have a very simple read/write
> + * handling, some common function will take care of it. Nevertheless some cases
> + * (read tasks) are special and therefore I define this structure for every
> + * kind of file.
> + *
> + *
> + * When reading/writing to a file:
> + *	- the container to use in file->f_dentry->d_parent->d_fsdata
> + *	- the 'cftype' of the file is file->f_dentry->d_fsdata
> + */
> +
> +struct inode;
> +#define MAX_CFTYPE_NAME 64
> +struct cftype {
> +	/* By convention, the name should begin with the name of the
> +	 * subsystem, followed by a period */
> +	char name[MAX_CFTYPE_NAME];
> +	int private;
> +	int (*open) (struct inode *inode, struct file *file);
> +	ssize_t (*read) (struct container *cont, struct cftype *cft,
> +			 struct file *file,
> +			 char __user *buf, size_t nbytes, loff_t *ppos);
> +	u64 (*read_uint) (struct container *cont, struct cftype *cft);

Is this a new callback, a specialization of the read() callback?

> +	ssize_t (*write) (struct container *cont, struct cftype *cft,
> +			  struct file *file,
> +			  const char __user *buf, size_t nbytes, loff_t *ppos);
> +	int (*release) (struct inode *inode, struct file *file);
> +};
> +

[snip]

-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL