kernel-ark/include/linux/configfs.h
Joel Becker 631d1febab configfs: config item dependancies.
Sometimes other drivers depend on particular configfs items.  For
example, ocfs2 mounts depend on a heartbeat region item.  If that
region item is removed with rmdir(2), the ocfs2 mount must BUG or go
readonly.  Not happy.

This provides two additional API calls: configfs_depend_item() and
configfs_undepend_item().  A client driver can call
configfs_depend_item() on an existing item to tell configfs that it is
depended on.  configfs will then return -EBUSY from rmdir(2) for that
item.  When the item is no longer depended on, the client driver calls
configfs_undepend_item() on it.

These API cannot be called underneath any configfs callbacks, as
they will conflict.  They can block and allocate.  A client driver
probably shouldn't calling them of its own gumption.  Rather it should
be providing an API that external subsystems call.

How does this work?  Imagine the ocfs2 mount process.  When it mounts,
it asks for a heart region item.  This is done via a call into the
heartbeat code.  Inside the heartbeat code, the region item is looked
up.  Here, the heartbeat code calls configfs_depend_item().  If it
succeeds, then heartbeat knows the region is safe to give to ocfs2.
If it fails, it was being torn down anyway, and heartbeat can gracefully
pass up an error.

[ Fixed some bad whitespace in configfs.txt. --Mark ]

Signed-off-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>
2007-07-10 17:18:59 -07:00

199 lines
6.4 KiB
C

/* -*- mode: c; c-basic-offset: 8; -*-
* vim: noexpandtab sw=8 ts=8 sts=0:
*
* configfs.h - definitions for the device driver filesystem
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public
* License along with this program; if not, write to the
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 021110-1307, USA.
*
* Based on sysfs:
* sysfs is Copyright (C) 2001, 2002, 2003 Patrick Mochel
*
* Based on kobject.h:
* Copyright (c) 2002-2003 Patrick Mochel
* Copyright (c) 2002-2003 Open Source Development Labs
*
* configfs Copyright (C) 2005 Oracle. All rights reserved.
*
* Please read Documentation/filesystems/configfs.txt before using the
* configfs interface, ESPECIALLY the parts about reference counts and
* item destructors.
*/
#ifndef _CONFIGFS_H_
#define _CONFIGFS_H_
#ifdef __KERNEL__
#include <linux/types.h>
#include <linux/list.h>
#include <linux/kref.h>
#include <linux/mutex.h>
#include <asm/atomic.h>
#define CONFIGFS_ITEM_NAME_LEN 20
struct module;
struct configfs_item_operations;
struct configfs_group_operations;
struct configfs_attribute;
struct configfs_subsystem;
struct config_item {
char *ci_name;
char ci_namebuf[CONFIGFS_ITEM_NAME_LEN];
struct kref ci_kref;
struct list_head ci_entry;
struct config_item *ci_parent;
struct config_group *ci_group;
struct config_item_type *ci_type;
struct dentry *ci_dentry;
};
extern int config_item_set_name(struct config_item *, const char *, ...);
static inline char *config_item_name(struct config_item * item)
{
return item->ci_name;
}
extern void config_item_init(struct config_item *);
extern void config_item_init_type_name(struct config_item *item,
const char *name,
struct config_item_type *type);
extern struct config_item * config_item_get(struct config_item *);
extern void config_item_put(struct config_item *);
struct config_item_type {
struct module *ct_owner;
struct configfs_item_operations *ct_item_ops;
struct configfs_group_operations *ct_group_ops;
struct configfs_attribute **ct_attrs;
};
/**
* group - a group of config_items of a specific type, belonging
* to a specific subsystem.
*/
struct config_group {
struct config_item cg_item;
struct list_head cg_children;
struct configfs_subsystem *cg_subsys;
struct config_group **default_groups;
};
extern void config_group_init(struct config_group *group);
extern void config_group_init_type_name(struct config_group *group,
const char *name,
struct config_item_type *type);
static inline struct config_group *to_config_group(struct config_item *item)
{
return item ? container_of(item,struct config_group,cg_item) : NULL;
}
static inline struct config_group *config_group_get(struct config_group *group)
{
return group ? to_config_group(config_item_get(&group->cg_item)) : NULL;
}
static inline void config_group_put(struct config_group *group)
{
config_item_put(&group->cg_item);
}
extern struct config_item *config_group_find_item(struct config_group *,
const char *);
struct configfs_attribute {
const char *ca_name;
struct module *ca_owner;
mode_t ca_mode;
};
/*
* Users often need to create attribute structures for their configurable
* attributes, containing a configfs_attribute member and function pointers
* for the show() and store() operations on that attribute. They can use
* this macro (similar to sysfs' __ATTR) to make defining attributes easier.
*/
#define __CONFIGFS_ATTR(_name, _mode, _show, _store) \
{ \
.attr = { \
.ca_name = __stringify(_name), \
.ca_mode = _mode, \
.ca_owner = THIS_MODULE, \
}, \
.show = _show, \
.store = _store, \
}
/*
* If allow_link() exists, the item can symlink(2) out to other
* items. If the item is a group, it may support mkdir(2).
* Groups supply one of make_group() and make_item(). If the
* group supports make_group(), one can create group children. If it
* supports make_item(), one can create config_item children. If it has
* default_groups on group->default_groups, it has automatically created
* group children. default_groups may coexist alongsize make_group() or
* make_item(), but if the group wishes to have only default_groups
* children (disallowing mkdir(2)), it need not provide either function.
* If the group has commit(), it supports pending and commited (active)
* items.
*/
struct configfs_item_operations {
void (*release)(struct config_item *);
ssize_t (*show_attribute)(struct config_item *, struct configfs_attribute *,char *);
ssize_t (*store_attribute)(struct config_item *,struct configfs_attribute *,const char *, size_t);
int (*allow_link)(struct config_item *src, struct config_item *target);
int (*drop_link)(struct config_item *src, struct config_item *target);
};
struct configfs_group_operations {
struct config_item *(*make_item)(struct config_group *group, const char *name);
struct config_group *(*make_group)(struct config_group *group, const char *name);
int (*commit_item)(struct config_item *item);
void (*disconnect_notify)(struct config_group *group, struct config_item *item);
void (*drop_item)(struct config_group *group, struct config_item *item);
};
struct configfs_subsystem {
struct config_group su_group;
struct mutex su_mutex;
};
static inline struct configfs_subsystem *to_configfs_subsystem(struct config_group *group)
{
return group ?
container_of(group, struct configfs_subsystem, su_group) :
NULL;
}
int configfs_register_subsystem(struct configfs_subsystem *subsys);
void configfs_unregister_subsystem(struct configfs_subsystem *subsys);
/* These functions can sleep and can alloc with GFP_KERNEL */
/* WARNING: These cannot be called underneath configfs callbacks!! */
int configfs_depend_item(struct configfs_subsystem *subsys, struct config_item *target);
void configfs_undepend_item(struct configfs_subsystem *subsys, struct config_item *target);
#endif /* __KERNEL__ */
#endif /* _CONFIGFS_H_ */