text: /*
   * linux/ipc/util.c
   * Copyright (C) 1992 Krishna Balasubramanian
   *
   * Sep 1997 - Call suser() last after "normal" permission checks so we
   *            get BSD style process accounting right.
   *            Occurs in several places in the IPC code.
   *            Chris Evans, <chris@ferret.lmh.ox.ac.uk>
   * Nov 1999 - ipc helper functions, unified SMP locking
   *	      Manfred Spraul <manfred@colorfullife.com>
   * Oct 2002 - One lock per IPC id. RCU ipc_free for lock-free grow_ary().
   *            Mingming Cao <cmm@us.ibm.com>
   * Mar 2006 - support for audit of ipc object properties
   *            Dustin Kirkland <dustin.kirkland@us.ibm.com>
   * Jun 2006 - namespaces ssupport
   *            OpenVZ, SWsoft Inc.
   *            Pavel Emelianov <xemul@openvz.org>
   *
   * General sysv ipc locking scheme:
   *	rcu_read_lock()
   *          obtain the ipc object (kern_ipc_perm) by looking up the id in an idr
   *	    tree.
   *	    - perform initial checks (capabilities, auditing and permission,
   *	      etc).
   *	    - perform read-only operations, such as STAT, INFO commands.
   *	      acquire the ipc lock (kern_ipc_perm.lock) through
   *	      ipc_lock_object()
   *		- perform data updates, such as SET, RMID commands and
   *		  mechanism-specific operations (semop/semtimedop,
   *		  msgsnd/msgrcv, shmat/shmdt).
   *	    drop the ipc lock, through ipc_unlock_object().
   *	rcu_read_unlock()
   *
   *  The ids->rwsem must be taken when:
   *	- creating, removing and iterating the existing entries in ipc
   *	  identifier sets.
   *	- iterating through files under /proc/sysvipc/
   *
   *  Note that sems have a special fast path that avoids kern_ipc_perm.lock -
   *  see sem_lock().
   */
  
  #include <linux/mm.h>
  #include <linux/shm.h>
  #include <linux/init.h>
  #include <linux/msg.h>
  #include <linux/vmalloc.h>
  #include <linux/slab.h>
  #include <linux/notifier.h>
  #include <linux/capability.h>
  #include <linux/highuid.h>
  #include <linux/security.h>
  #include <linux/rcupdate.h>
  #include <linux/workqueue.h>
  #include <linux/seq_file.h>
  #include <linux/proc_fs.h>
  #include <linux/audit.h>
  #include <linux/nsproxy.h>
  #include <linux/rwsem.h>
  #include <linux/memory.h>
  #include <linux/ipc_namespace.h>
  
  #include <asm/unistd.h>
  
  #include "util.h"
  
  struct ipc_proc_iface {
  	const char *path;
  	const char *header;
  	int ids;
  	int (*show)(struct seq_file *, void *);
  };
  
  static void ipc_memory_notifier(struct work_struct *work)
  {
  	ipcns_notify(IPCNS_MEMCHANGED);
  }
  
  static int ipc_memory_callback(struct notifier_block *self,
  				unsigned long action, void *arg)
  {
  	static DECLARE_WORK(ipc_memory_wq, ipc_memory_notifier);
  
  	switch (action) {
  	case MEM_ONLINE:    /* memory successfully brought online */
  	case MEM_OFFLINE:   /* or offline: it's time to recompute msgmni */
  		/*
  		 * This is done by invoking the ipcns notifier chain with the
  		 * IPC_MEMCHANGED event.
  		 * In order not to keep the lock on the hotplug memory chain
  		 * for too long, queue a work item that will, when waken up,
  		 * activate the ipcns notification chain.
  		 */
  		schedule_work(&ipc_memory_wq);
  		break;
  	case MEM_GOING_ONLINE:
  	case MEM_GOING_OFFLINE:
  	case MEM_CANCEL_ONLINE:
  	case MEM_CANCEL_OFFLINE:
  	default:
  		break;
  	}
  
  	return NOTIFY_OK;
  }
  
  static struct notifier_block ipc_memory_nb = {
  	.notifier_call = ipc_memory_callback,
  	.priority = IPC_CALLBACK_PRI,
  };
  
  /**
   *	ipc_init	-	initialise IPC subsystem
   *
   *	The various system5 IPC resources (semaphores, messages and shared
   *	memory) are initialised
   *	A callback routine is registered into the memory hotplug notifier
   *	chain: since msgmni scales to lowmem this callback routine will be
   *	called upon successful memory add / remove to recompute msmgni.
   */
   
  static int __init ipc_init(void)
  {
  	sem_init();
  	msg_init();
  	shm_init();
  	register_hotmemory_notifier(&ipc_memory_nb);
  	register_ipcns_notifier(&init_ipc_ns);
  	return 0;
  }
  __initcall(ipc_init);
  
  /**
   *	ipc_init_ids		-	initialise IPC identifiers
   *	@ids: Identifier set
   *
   *	Set up the sequence range to use for the ipc identifier range (limited
   *	below IPCMNI) then initialise the ids idr.
   */
   
  void ipc_init_ids(struct ipc_ids *ids)
  {
  	init_rwsem(&ids->rwsem);
  
  	ids->in_use = 0;
  	ids->seq = 0;
  	ids->next_id = -1;
  	{
  		int seq_limit = INT_MAX/SEQ_MULTIPLIER;
  		if (seq_limit > USHRT_MAX)
  			ids->seq_max = USHRT_MAX;
  		 else
  		 	ids->seq_max = seq_limit;
  	}
  
  	idr_init(&ids->ipcs_idr);
  }
  
  #ifdef CONFIG_PROC_FS
  static const struct file_operations sysvipc_proc_fops;
  /**
   *	ipc_init_proc_interface	-  Create a proc interface for sysipc types using a seq_file interface.
   *	@path: Path in procfs
   *	@header: Banner to be printed at the beginning of the file.
   *	@ids: ipc id table to iterate.
   *	@show: show routine.
   */
  void __init ipc_init_proc_interface(const char *path, const char *header,
  		int ids, int (*show)(struct seq_file *, void *))
  {
  	struct proc_dir_entry *pde;
  	struct ipc_proc_iface *iface;
  
  	iface = kmalloc(sizeof(*iface), GFP_KERNEL);
  	if (!iface)
  		return;
  	iface->path	= path;
  	iface->header	= header;
  	iface->ids	= ids;
  	iface->show	= show;
  
  	pde = proc_create_data(path,
  			       S_IRUGO,        /* world readable */
  			       NULL,           /* parent dir */
  			       &sysvipc_proc_fops,
  			       iface);
  	if (!pde) {
  		kfree(iface);
  	}
  }
  #endif
  
  /**
   *	ipc_findkey	-	find a key in an ipc identifier set	
   *	@ids: Identifier set
   *	@key: The key to find
   *	
   *	Requires ipc_ids.rwsem locked.
   *	Returns the LOCKED pointer to the ipc structure if found or NULL
   *	if not.
   *	If key is found ipc points to the owning ipc structure
   */
   
  static struct kern_ipc_perm *ipc_findkey(struct ipc_ids *ids, key_t key)
  {
  	struct kern_ipc_perm *ipc;
  	int next_id;
  	int total;
  
  	for (total = 0, next_id = 0; total < ids->in_use; next_id++) {
  		ipc = idr_find(&ids->ipcs_idr, next_id);
  
  		if (ipc == NULL)
  			continue;
  
  		if (ipc->key != key) {
  			total++;
  			continue;
  		}
  
  		rcu_read_lock();
  		ipc_lock_object(ipc);
  		return ipc;
  	}
  
  	return NULL;
  }
  
  /**
   *	ipc_get_maxid 	-	get the last assigned id
   *	@ids: IPC identifier set
   *
   *	Called with ipc_ids.rwsem held.
   */
  
  int ipc_get_maxid(struct ipc_ids *ids)
  {
  	struct kern_ipc_perm *ipc;
  	int max_id = -1;
  	int total, id;
  
  	if (ids->in_use == 0)
  		return -1;
  
  	if (ids->in_use == IPCMNI)
  		return IPCMNI - 1;
  
  	/* Look for the last assigned id */
  	total = 0;
  	for (id = 0; id < IPCMNI && total < ids->in_use; id++) {
  		ipc = idr_find(&ids->ipcs_idr, id);
  		if (ipc != NULL) {
  			max_id = id;
  			total++;
  		}
  	}
  	return max_id;
  }
  
  /**
   *	ipc_addid 	-	add an IPC identifier
   *	@ids: IPC identifier set
   *	@new: new IPC permission set
   *	@size: limit for the number of used ids
   *
   *	Add an entry 'new' to the IPC ids idr. The permissions object is
   *	initialised and the first free entry is set up and the id assigned
   *	is returned. The 'new' entry is returned in a locked state on success.
   *	On failure the entry is not locked and a negative err-code is returned.
   *
   *	Called with writer ipc_ids.rwsem held.
   */
  int ipc_addid(struct ipc_ids* ids, struct kern_ipc_perm* new, int size)
  {
  	kuid_t euid;
  	kgid_t egid;
  	int id;
  	int next_id = ids->next_id;
  
  	if (size > IPCMNI)
  		size = IPCMNI;
  
  	if (ids->in_use >= size)
  		return -ENOSPC;
  
  	idr_preload(GFP_KERNEL);
  
  	spin_lock_init(&new->lock);
  	new->deleted = 0;
  	rcu_read_lock();
  	spin_lock(&new->lock);
  
  	current_euid_egid(&euid, &egid);
  	new->cuid = new->uid = euid;
  	new->gid = new->cgid = egid;
  
  	id = idr_alloc(&ids->ipcs_idr, new,
  		       (next_id < 0) ? 0 : ipcid_to_idx(next_id), 0,
  		       GFP_NOWAIT);
  	idr_preload_end();
  	if (id < 0) {
  		spin_unlock(&new->lock);
  		rcu_read_unlock();
  		return id;
  	}
  
  	ids->in_use++;
  
  	if (next_id < 0) {
  		new->seq = ids->seq++;
  		if (ids->seq > ids->seq_max)
  			ids->seq = 0;
  	} else {
  		new->seq = ipcid_to_seqx(next_id);
  		ids->next_id = -1;
  	}
  
  	new->id = ipc_buildid(id, new->seq);
  	return id;
  }
  
  /**
   *	ipcget_new	-	create a new ipc object
   *	@ns: namespace
   *	@ids: IPC identifer set
   *	@ops: the actual creation routine to call
   *	@params: its parameters
   *
   *	This routine is called by sys_msgget, sys_semget() and sys_shmget()
   *	when the key is IPC_PRIVATE.
   */
  static int ipcget_new(struct ipc_namespace *ns, struct ipc_ids *ids,
  		struct ipc_ops *ops, struct ipc_params *params)
  {
  	int err;
  
  	down_write(&ids->rwsem);
  	err = ops->getnew(ns, params);
  	up_write(&ids->rwsem);
  	return err;
  }
  
  /**
   *	ipc_check_perms	-	check security and permissions for an IPC
   *	@ns: IPC namespace
   *	@ipcp: ipc permission set
   *	@ops: the actual security routine to call
   *	@params: its parameters
   *
   *	This routine is called by sys_msgget(), sys_semget() and sys_shmget()
   *      when the key is not IPC_PRIVATE and that key already exists in the
   *      ids IDR.
   *
   *	On success, the IPC id is returned.
   *
   *	It is called with ipc_ids.rwsem and ipcp->lock held.
   */
  static int ipc_check_perms(struct ipc_namespace *ns,
  			   struct kern_ipc_perm *ipcp,
  			   struct ipc_ops *ops,
  			   struct ipc_params *params)
  {
  	int err;
  
  	if (ipcperms(ns, ipcp, params->flg))
  		err = -EACCES;
  	else {
  		err = ops->associate(ipcp, params->flg);
  		if (!err)
  			err = ipcp->id;
  	}
  
  	return err;
  }
  
  /**
   *	ipcget_public	-	get an ipc object or create a new one
   *	@ns: namespace
   *	@ids: IPC identifer set
   *	@ops: the actual creation routine to call
   *	@params: its parameters
   *
   *	This routine is called by sys_msgget, sys_semget() and sys_shmget()
   *	when the key is not IPC_PRIVATE.
   *	It adds a new entry if the key is not found and does some permission
   *      / security checkings if the key is found.
   *
   *	On success, the ipc id is returned.
   */
  static int ipcget_public(struct ipc_namespace *ns, struct ipc_ids *ids,
  		struct ipc_ops *ops, struct ipc_params *params)
  {
  	struct kern_ipc_perm *ipcp;
  	int flg = params->flg;
  	int err;
  
  	/*
  	 * Take the lock as a writer since we are potentially going to add
  	 * a new entry + read locks are not "upgradable"
  	 */
  	down_write(&ids->rwsem);
  	ipcp = ipc_findkey(ids, params->key);
  	if (ipcp == NULL) {
  		/* key not used */
  		if (!(flg & IPC_CREAT))
  			err = -ENOENT;
  		else
  			err = ops->getnew(ns, params);
  	} else {
  		/* ipc object has been locked by ipc_findkey() */
  
  		if (flg & IPC_CREAT && flg & IPC_EXCL)
  			err = -EEXIST;
  		else {
  			err = 0;
  			if (ops->more_checks)
  				err = ops->more_checks(ipcp, params);
  			if (!err)
  				/*
  				 * ipc_check_perms returns the IPC id on
  				 * success
  				 */
  				err = ipc_check_perms(ns, ipcp, ops, params);
  		}
  		ipc_unlock(ipcp);
  	}
  	up_write(&ids->rwsem);
  
  	return err;
  }
  
  
  /**
   *	ipc_rmid	-	remove an IPC identifier
   *	@ids: IPC identifier set
   *	@ipcp: ipc perm structure containing the identifier to remove
   *
   *	ipc_ids.rwsem (as a writer) and the spinlock for this ID are held
   *	before this function is called, and remain locked on the exit.
   */
   
  void ipc_rmid(struct ipc_ids *ids, struct kern_ipc_perm *ipcp)
  {
  	int lid = ipcid_to_idx(ipcp->id);
  
  	idr_remove(&ids->ipcs_idr, lid);
  
  	ids->in_use--;
  
  	ipcp->deleted = 1;
  
  	return;
  }
  
  /**
   *	ipc_alloc	-	allocate ipc space
   *	@size: size desired
   *
   *	Allocate memory from the appropriate pools and return a pointer to it.
   *	NULL is returned if the allocation fails
   */
   
  void *ipc_alloc(int size)
  {
  	void *out;
  	if(size > PAGE_SIZE)
  		out = vmalloc(size);
  	else
  		out = kmalloc(size, GFP_KERNEL);
  	return out;
  }
  
  /**
   *	ipc_free        -       free ipc space
   *	@ptr: pointer returned by ipc_alloc
   *	@size: size of block
   *
   *	Free a block created with ipc_alloc(). The caller must know the size
   *	used in the allocation call.
   */
  
  void ipc_free(void* ptr, int size)
  {
  	if(size > PAGE_SIZE)
  		vfree(ptr);
  	else
  		kfree(ptr);
  }
  
  /**
   *	ipc_rcu_alloc	-	allocate ipc and rcu space 
   *	@size: size desired
   *
   *	Allocate memory for the rcu header structure +  the object.
   *	Returns the pointer to the object or NULL upon failure.
   */
  void *ipc_rcu_alloc(int size)
  {
  	/*
  	 * We prepend the allocation with the rcu struct
  	 */
  	struct ipc_rcu *out = ipc_alloc(sizeof(struct ipc_rcu) + size);
  	if (unlikely(!out))
  		return NULL;
  	atomic_set(&out->refcount, 1);
  	return out + 1;
  }
  
  int ipc_rcu_getref(void *ptr)
  {
  	struct ipc_rcu *p = ((struct ipc_rcu *)ptr) - 1;
  
  	return atomic_inc_not_zero(&p->refcount);
  }
  
  void ipc_rcu_putref(void *ptr, void (*func)(struct rcu_head *head))
  {
  	struct ipc_rcu *p = ((struct ipc_rcu *)ptr) - 1;
  
  	if (!atomic_dec_and_test(&p->refcount))
  		return;
  
  	call_rcu(&p->rcu, func);
  }
  
  void ipc_rcu_free(struct rcu_head *head)
  {
  	struct ipc_rcu *p = container_of(head, struct ipc_rcu, rcu);
  
  	if (is_vmalloc_addr(p))
  		vfree(p);
  	else
  		kfree(p);
  }
  
  /**
   *	ipcperms	-	check IPC permissions
   *	@ns: IPC namespace
   *	@ipcp: IPC permission set
   *	@flag: desired permission set.
   *
   *	Check user, group, other permissions for access
   *	to ipc resources. return 0 if allowed
   *
   * 	@flag will most probably be 0 or S_...UGO from <linux/stat.h>
   */
   
  int ipcperms(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp, short flag)
  {
  	kuid_t euid = current_euid();
  	int requested_mode, granted_mode;
  
  	audit_ipc_obj(ipcp);
  	requested_mode = (flag >> 6) | (flag >> 3) | flag;
  	granted_mode = ipcp->mode;
  	if (uid_eq(euid, ipcp->cuid) ||
  	    uid_eq(euid, ipcp->uid))
  		granted_mode >>= 6;
  	else if (in_group_p(ipcp->cgid) || in_group_p(ipcp->gid))
  		granted_mode >>= 3;
  	/* is there some bit set in requested_mode but not in granted_mode? */
  	if ((requested_mode & ~granted_mode & 0007) && 
  	    !ns_capable(ns->user_ns, CAP_IPC_OWNER))
  		return -1;
  
  	return security_ipc_permission(ipcp, flag);
  }
  
  /*
   * Functions to convert between the kern_ipc_perm structure and the
   * old/new ipc_perm structures
   */
  
  /**
   *	kernel_to_ipc64_perm	-	convert kernel ipc permissions to user
   *	@in: kernel permissions
   *	@out: new style IPC permissions
   *
   *	Turn the kernel object @in into a set of permissions descriptions
   *	for returning to userspace (@out).
   */
   
  
  void kernel_to_ipc64_perm (struct kern_ipc_perm *in, struct ipc64_perm *out)
  {
  	out->key	= in->key;
  	out->uid	= from_kuid_munged(current_user_ns(), in->uid);
  	out->gid	= from_kgid_munged(current_user_ns(), in->gid);
  	out->cuid	= from_kuid_munged(current_user_ns(), in->cuid);
  	out->cgid	= from_kgid_munged(current_user_ns(), in->cgid);
  	out->mode	= in->mode;
  	out->seq	= in->seq;
  }
  
  /**
   *	ipc64_perm_to_ipc_perm	-	convert new ipc permissions to old
   *	@in: new style IPC permissions
   *	@out: old style IPC permissions
   *
   *	Turn the new style permissions object @in into a compatibility
   *	object and store it into the @out pointer.
   */
   
  void ipc64_perm_to_ipc_perm (struct ipc64_perm *in, struct ipc_perm *out)
  {
  	out->key	= in->key;
  	SET_UID(out->uid, in->uid);
  	SET_GID(out->gid, in->gid);
  	SET_UID(out->cuid, in->cuid);
  	SET_GID(out->cgid, in->cgid);
  	out->mode	= in->mode;
  	out->seq	= in->seq;
  }
  
  /**
   * ipc_obtain_object
   * @ids: ipc identifier set
   * @id: ipc id to look for
   *
   * Look for an id in the ipc ids idr and return associated ipc object.
   *
   * Call inside the RCU critical section.
   * The ipc object is *not* locked on exit.
   */
  struct kern_ipc_perm *ipc_obtain_object(struct ipc_ids *ids, int id)
  {
  	struct kern_ipc_perm *out;
  	int lid = ipcid_to_idx(id);
  
  	out = idr_find(&ids->ipcs_idr, lid);
  	if (!out)
  		return ERR_PTR(-EINVAL);
  
  	return out;
  }
  
  /**
   * ipc_lock - Lock an ipc structure without rwsem held
   * @ids: IPC identifier set
   * @id: ipc id to look for
   *
   * Look for an id in the ipc ids idr and lock the associated ipc object.
   *
   * The ipc object is locked on successful exit.
   */
  struct kern_ipc_perm *ipc_lock(struct ipc_ids *ids, int id)
  {
  	struct kern_ipc_perm *out;
  
  	rcu_read_lock();
  	out = ipc_obtain_object(ids, id);
  	if (IS_ERR(out))
  		goto err1;
  
  	spin_lock(&out->lock);
  
  	/* ipc_rmid() may have already freed the ID while ipc_lock
  	 * was spinning: here verify that the structure is still valid
  	 */
  	if (!out->deleted)
  		return out;
  
  	spin_unlock(&out->lock);
  	out = ERR_PTR(-EINVAL);
  err1:
  	rcu_read_unlock();
  	return out;
  }
  
  /**
   * ipc_obtain_object_check
   * @ids: ipc identifier set
   * @id: ipc id to look for
   *
   * Similar to ipc_obtain_object() but also checks
   * the ipc object reference counter.
   *
   * Call inside the RCU critical section.
   * The ipc object is *not* locked on exit.
   */
  struct kern_ipc_perm *ipc_obtain_object_check(struct ipc_ids *ids, int id)
  {
  	struct kern_ipc_perm *out = ipc_obtain_object(ids, id);
  
  	if (IS_ERR(out))
  		goto out;
  
  	if (ipc_checkid(out, id))
  		return ERR_PTR(-EIDRM);
  out:
  	return out;
  }
  
  /**
   * ipcget - Common sys_*get() code
   * @ns : namsepace
   * @ids : IPC identifier set
   * @ops : operations to be called on ipc object creation, permission checks
   *        and further checks
   * @params : the parameters needed by the previous operations.
   *
   * Common routine called by sys_msgget(), sys_semget() and sys_shmget().
   */
  int ipcget(struct ipc_namespace *ns, struct ipc_ids *ids,
  			struct ipc_ops *ops, struct ipc_params *params)
  {
  	if (params->key == IPC_PRIVATE)
  		return ipcget_new(ns, ids, ops, params);
  	else
  		return ipcget_public(ns, ids, ops, params);
  }
  
  /**
   * ipc_update_perm - update the permissions of an IPC.
   * @in:  the permission given as input.
   * @out: the permission of the ipc to set.
   */
  int ipc_update_perm(struct ipc64_perm *in, struct kern_ipc_perm *out)
  {
  	kuid_t uid = make_kuid(current_user_ns(), in->uid);
  	kgid_t gid = make_kgid(current_user_ns(), in->gid);
  	if (!uid_valid(uid) || !gid_valid(gid))
  		return -EINVAL;
  
  	out->uid = uid;
  	out->gid = gid;
  	out->mode = (out->mode & ~S_IRWXUGO)
  		| (in->mode & S_IRWXUGO);
  
  	return 0;
  }
  
  /**
   * ipcctl_pre_down_nolock - retrieve an ipc and check permissions for some IPC_XXX cmd
   * @ns:  the ipc namespace
   * @ids:  the table of ids where to look for the ipc
   * @id:   the id of the ipc to retrieve
   * @cmd:  the cmd to check
   * @perm: the permission to set
   * @extra_perm: one extra permission parameter used by msq
   *
   * This function does some common audit and permissions check for some IPC_XXX
   * cmd and is called from semctl_down, shmctl_down and msgctl_down.
   * It must be called without any lock held and
   *  - retrieves the ipc with the given id in the given table.
   *  - performs some audit and permission check, depending on the given cmd
   *  - returns a pointer to the ipc object or otherwise, the corresponding error.
   *
   * Call holding the both the rwsem and the rcu read lock.
   */
  struct kern_ipc_perm *ipcctl_pre_down_nolock(struct ipc_namespace *ns,
  					struct ipc_ids *ids, int id, int cmd,
  					struct ipc64_perm *perm, int extra_perm)
  {
  	kuid_t euid;
  	int err = -EPERM;
  	struct kern_ipc_perm *ipcp;
  
  	ipcp = ipc_obtain_object_check(ids, id);
  	if (IS_ERR(ipcp)) {
  		err = PTR_ERR(ipcp);
  		goto err;
  	}
  
  	audit_ipc_obj(ipcp);
  	if (cmd == IPC_SET)
  		audit_ipc_set_perm(extra_perm, perm->uid,
  				   perm->gid, perm->mode);
  
  	euid = current_euid();
  	if (uid_eq(euid, ipcp->cuid) || uid_eq(euid, ipcp->uid)  ||
  	    ns_capable(ns->user_ns, CAP_SYS_ADMIN))
  		return ipcp; /* successful lookup */
  err:
  	return ERR_PTR(err);
  }
  
  #ifdef CONFIG_ARCH_WANT_IPC_PARSE_VERSION
  
  
  /**
   *	ipc_parse_version	-	IPC call version
   *	@cmd: pointer to command
   *
   *	Return IPC_64 for new style IPC and IPC_OLD for old style IPC. 
   *	The @cmd value is turned from an encoding command and version into
   *	just the command code.
   */
   
  int ipc_parse_version (int *cmd)
  {
  	if (*cmd & IPC_64) {
  		*cmd ^= IPC_64;
  		return IPC_64;
  	} else {
  		return IPC_OLD;
  	}
  }
  
  #endif /* CONFIG_ARCH_WANT_IPC_PARSE_VERSION */
  
  #ifdef CONFIG_PROC_FS
  struct ipc_proc_iter {
  	struct ipc_namespace *ns;
  	struct ipc_proc_iface *iface;
  };
  
  /*
   * This routine locks the ipc structure found at least at position pos.
   */
  static struct kern_ipc_perm *sysvipc_find_ipc(struct ipc_ids *ids, loff_t pos,
  					      loff_t *new_pos)
  {
  	struct kern_ipc_perm *ipc;
  	int total, id;
  
  	total = 0;
  	for (id = 0; id < pos && total < ids->in_use; id++) {
  		ipc = idr_find(&ids->ipcs_idr, id);
  		if (ipc != NULL)
  			total++;
  	}
  
  	if (total >= ids->in_use)
  		return NULL;
  
  	for ( ; pos < IPCMNI; pos++) {
  		ipc = idr_find(&ids->ipcs_idr, pos);
  		if (ipc != NULL) {
  			*new_pos = pos + 1;
  			rcu_read_lock();
  			ipc_lock_object(ipc);
  			return ipc;
  		}
  	}
  
  	/* Out of range - return NULL to terminate iteration */
  	return NULL;
  }
  
  static void *sysvipc_proc_next(struct seq_file *s, void *it, loff_t *pos)
  {
  	struct ipc_proc_iter *iter = s->private;
  	struct ipc_proc_iface *iface = iter->iface;
  	struct kern_ipc_perm *ipc = it;
  
  	/* If we had an ipc id locked before, unlock it */
  	if (ipc && ipc != SEQ_START_TOKEN)
  		ipc_unlock(ipc);
  
  	return sysvipc_find_ipc(&iter->ns->ids[iface->ids], *pos, pos);
  }
  
  /*
   * File positions: pos 0 -> header, pos n -> ipc id = n - 1.
   * SeqFile iterator: iterator value locked ipc pointer or SEQ_TOKEN_START.
   */
  static void *sysvipc_proc_start(struct seq_file *s, loff_t *pos)
  {
  	struct ipc_proc_iter *iter = s->private;
  	struct ipc_proc_iface *iface = iter->iface;
  	struct ipc_ids *ids;
  
  	ids = &iter->ns->ids[iface->ids];
  
  	/*
  	 * Take the lock - this will be released by the corresponding
  	 * call to stop().
  	 */
  	down_read(&ids->rwsem);
  
  	/* pos < 0 is invalid */
  	if (*pos < 0)
  		return NULL;
  
  	/* pos == 0 means header */
  	if (*pos == 0)
  		return SEQ_START_TOKEN;
  
  	/* Find the (pos-1)th ipc */
  	return sysvipc_find_ipc(ids, *pos - 1, pos);
  }
  
  static void sysvipc_proc_stop(struct seq_file *s, void *it)
  {
  	struct kern_ipc_perm *ipc = it;
  	struct ipc_proc_iter *iter = s->private;
  	struct ipc_proc_iface *iface = iter->iface;
  	struct ipc_ids *ids;
  
  	/* If we had a locked structure, release it */
  	if (ipc && ipc != SEQ_START_TOKEN)
  		ipc_unlock(ipc);
  
  	ids = &iter->ns->ids[iface->ids];
  	/* Release the lock we took in start() */
  	up_read(&ids->rwsem);
  }
  
  static int sysvipc_proc_show(struct seq_file *s, void *it)
  {
  	struct ipc_proc_iter *iter = s->private;
  	struct ipc_proc_iface *iface = iter->iface;
  
  	if (it == SEQ_START_TOKEN)
  		return seq_puts(s, iface->header);
  
  	return iface->show(s, it);
  }
  
  static const struct seq_operations sysvipc_proc_seqops = {
  	.start = sysvipc_proc_start,
  	.stop  = sysvipc_proc_stop,
  	.next  = sysvipc_proc_next,
  	.show  = sysvipc_proc_show,
  };
  
  static int sysvipc_proc_open(struct inode *inode, struct file *file)
  {
  	int ret;
  	struct seq_file *seq;
  	struct ipc_proc_iter *iter;
  
  	ret = -ENOMEM;
  	iter = kmalloc(sizeof(*iter), GFP_KERNEL);
  	if (!iter)
  		goto out;
  
  	ret = seq_open(file, &sysvipc_proc_seqops);
  	if (ret)
  		goto out_kfree;
  
  	seq = file->private_data;
  	seq->private = iter;
  
  	iter->iface = PDE_DATA(inode);
  	iter->ns    = get_ipc_ns(current->nsproxy->ipc_ns);
  out:
  	return ret;
  out_kfree:
  	kfree(iter);
  	goto out;
  }
  
  static int sysvipc_proc_release(struct inode *inode, struct file *file)
  {
  	struct seq_file *seq = file->private_data;
  	struct ipc_proc_iter *iter = seq->private;
  	put_ipc_ns(iter->ns);
  	return seq_release_private(inode, file);
  }
  
  static const struct file_operations sysvipc_proc_fops = {
  	.open    = sysvipc_proc_open,
  	.read    = seq_read,
  	.llseek  = seq_lseek,
  	.release = sysvipc_proc_release,
  };
  #endif /* CONFIG_PROC_FS */
  