union_subr.c

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/*
 * Copyright (c) 1994 Jan-Simon Pendry
 * Copyright (c) 1994
 *	The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Jan-Simon Pendry.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *	@(#)union_subr.c	8.4 (Berkeley) 2/17/94
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/time.h>
#include <sys/kernel.h>
#include <sys/vnode.h>
#include <sys/namei.h>
#include <sys/malloc.h>
#include <sys/file.h>
#include <sys/filedesc.h>
#include <sys/queue.h>
#include <miscfs/union/union.h>

#ifdef DIAGNOSTIC
#include <sys/proc.h>
#endif

/* must be power of two, otherwise change UNION_HASH() */
#define NHASH 32

/* unsigned int ... */
#define UNION_HASH(u, l) \
	(((((unsigned long) (u)) + ((unsigned long) l)) >> 8) & (NHASH-1))

static LIST_HEAD(unhead, union_node) unhead[NHASH];
static int unvplock[NHASH];

int
union_init()
{
	int i;

	for (i = 0; i < NHASH; i++)
		LIST_INIT(&unhead[i]);
	bzero((caddr_t) unvplock, sizeof(unvplock));
}

static int
union_list_lock(ix)
	int ix;
{

	if (unvplock[ix] & UN_LOCKED) {
		unvplock[ix] |= UN_WANT;
		sleep((caddr_t) &unvplock[ix], PINOD);
		return (1);
	}

	unvplock[ix] |= UN_LOCKED;

	return (0);
}

static void
union_list_unlock(ix)
	int ix;
{

	unvplock[ix] &= ~UN_LOCKED;

	if (unvplock[ix] & UN_WANT) {
		unvplock[ix] &= ~UN_WANT;
		wakeup((caddr_t) &unvplock[ix]);
	}
}

void
union_updatevp(un, uppervp, lowervp)
	struct union_node *un;
	struct vnode *uppervp;
	struct vnode *lowervp;
{
	int ohash = UNION_HASH(un->un_uppervp, un->un_lowervp);
	int nhash = UNION_HASH(uppervp, lowervp);

	if (ohash != nhash) {
		/*
		 * Ensure locking is ordered from lower to higher
		 * to avoid deadlocks.
		 */
		if (nhash < ohash) {
			int t = ohash;
			ohash = nhash;
			nhash = t;
		}

		while (union_list_lock(ohash))
			continue;

		while (union_list_lock(nhash))
			continue;

		LIST_REMOVE(un, un_cache);
		union_list_unlock(ohash);
	} else {	
		while (union_list_lock(nhash))
			continue;
	}

	if (un->un_lowervp != lowervp) {
		if (un->un_lowervp) {
			vrele(un->un_lowervp);
			if (un->un_path) {
				free(un->un_path, M_TEMP);
				un->un_path = 0;
			}
			if (un->un_dirvp) {
				vrele(un->un_dirvp);
				un->un_dirvp = NULLVP;
			}
		}
		un->un_lowervp = lowervp;
	}

	if (un->un_uppervp != uppervp) {
		if (un->un_uppervp)
			vrele(un->un_uppervp);

		un->un_uppervp = uppervp;
	}

	if (ohash != nhash)
		LIST_INSERT_HEAD(&unhead[nhash], un, un_cache);

	union_list_unlock(nhash);
}

void
union_newlower(un, lowervp)
	struct union_node *un;
	struct vnode *lowervp;
{

	union_updatevp(un, un->un_uppervp, lowervp);
}

void
union_newupper(un, uppervp)
	struct union_node *un;
	struct vnode *uppervp;
{

	union_updatevp(un, uppervp, un->un_lowervp);
}

/*
 * allocate a union_node/vnode pair.  the vnode is
 * referenced and locked.  the new vnode is returned
 * via (vpp).  (mp) is the mountpoint of the union filesystem,
 * (dvp) is the parent directory where the upper layer object
 * should exist (but doesn't) and (cnp) is the componentname
 * information which is partially copied to allow the upper
 * layer object to be created at a later time.  (uppervp)
 * and (lowervp) reference the upper and lower layer objects
 * being mapped.  either, but not both, can be nil.
 * if supplied, (uppervp) is locked.
 * the reference is either maintained in the new union_node
 * object which is allocated, or they are vrele'd.
 *
 * all union_nodes are maintained on a singly-linked
 * list.  new nodes are only allocated when they cannot
 * be found on this list.  entries on the list are
 * removed when the vfs reclaim entry is called.
 *
 * a single lock is kept for the entire list.  this is
 * needed because the getnewvnode() function can block
 * waiting for a vnode to become free, in which case there
 * may be more than one process trying to get the same
 * vnode.  this lock is only taken if we are going to
 * call getnewvnode, since the kernel itself is single-threaded.
 *
 * if an entry is found on the list, then call vget() to
 * take a reference.  this is done because there may be
 * zero references to it and so it needs to removed from
 * the vnode free list.
 */
int
union_allocvp(vpp, mp, undvp, dvp, cnp, uppervp, lowervp)
	struct vnode **vpp;
	struct mount *mp;
	struct vnode *undvp;
	struct vnode *dvp;		/* may be null */
	struct componentname *cnp;	/* may be null */
	struct vnode *uppervp;		/* may be null */
	struct vnode *lowervp;		/* may be null */
{
	int error;
	struct union_node *un;
	struct union_node **pp;
	struct vnode *xlowervp = NULLVP;
	int hash;
	int try;

	if (uppervp == NULLVP && lowervp == NULLVP)
		panic("union: unidentifiable allocation");

	if (uppervp && lowervp && (uppervp->v_type != lowervp->v_type)) {
		xlowervp = lowervp;
		lowervp = NULLVP;
	}

loop:
	for (try = 0; try < 3; try++) {
		switch (try) {
		case 0:
			if (lowervp == NULLVP)
				continue;
			hash = UNION_HASH(uppervp, lowervp);
			break;

		case 1:
			if (uppervp == NULLVP)
				continue;
			hash = UNION_HASH(uppervp, NULLVP);
			break;

		case 2:
			if (lowervp == NULLVP)
				continue;
			hash = UNION_HASH(NULLVP, lowervp);
			break;
		}

		while (union_list_lock(hash))
			continue;

		for (un = unhead[hash].lh_first; un != 0;
					un = un->un_cache.le_next) {
			if ((un->un_lowervp == lowervp ||
			     un->un_lowervp == NULLVP) &&
			    (un->un_uppervp == uppervp ||
			     un->un_uppervp == NULLVP) &&
			    (UNIONTOV(un)->v_mount == mp)) {
				if (vget(UNIONTOV(un), 0)) {
					union_list_unlock(hash);
					goto loop;
				}
				break;
			}
		}

		union_list_unlock(hash);

		if (un)
			break;
	}

	if (un) {
		/*
		 * Obtain a lock on the union_node.
		 * uppervp is locked, though un->un_uppervp
		 * may not be.  this doesn't break the locking
		 * hierarchy since in the case that un->un_uppervp
		 * is not yet locked it will be vrele'd and replaced
		 * with uppervp.
		 */

		if ((dvp != NULLVP) && (uppervp == dvp)) {
			/*
			 * Access ``.'', so (un) will already
			 * be locked.  Since this process has
			 * the lock on (uppervp) no other
			 * process can hold the lock on (un).
			 */
#ifdef DIAGNOSTIC
			if ((un->un_flags & UN_LOCKED) == 0)
				panic("union: . not locked");
			else if (curproc && un->un_pid != curproc->p_pid &&
				    un->un_pid > -1 && curproc->p_pid > -1)
				panic("union: allocvp not lock owner");
#endif
		} else {
			if (un->un_flags & UN_LOCKED) {
				vrele(UNIONTOV(un));
				un->un_flags |= UN_WANT;
				sleep((caddr_t) &un->un_flags, PINOD);
				goto loop;
			}
			un->un_flags |= UN_LOCKED;

#ifdef DIAGNOSTIC
			if (curproc)
				un->un_pid = curproc->p_pid;
			else
				un->un_pid = -1;
#endif
		}

		/*
		 * At this point, the union_node is locked,
		 * un->un_uppervp may not be locked, and uppervp
		 * is locked or nil.
		 */

		/*
		 * Save information about the upper layer.
		 */
		if (uppervp != un->un_uppervp) {
			union_newupper(un, uppervp);
		} else if (uppervp) {
			vrele(uppervp);
		}

		if (un->un_uppervp) {
			un->un_flags |= UN_ULOCK;
			un->un_flags &= ~UN_KLOCK;
		}

		/*
		 * Save information about the lower layer.
		 * This needs to keep track of pathname
		 * and directory information which union_vn_create
		 * might need.
		 */
		if (lowervp != un->un_lowervp) {
			union_newlower(un, lowervp);
			if (cnp && (lowervp != NULLVP) &&
			    (lowervp->v_type == VREG)) {
				un->un_hash = cnp->cn_hash;
				un->un_path = malloc(cnp->cn_namelen+1,
						M_TEMP, M_WAITOK);
				bcopy(cnp->cn_nameptr, un->un_path,
						cnp->cn_namelen);
				un->un_path[cnp->cn_namelen] = '\0';
				VREF(dvp);
				un->un_dirvp = dvp;
			}
		} else if (lowervp) {
			vrele(lowervp);
		}
		*vpp = UNIONTOV(un);
		return (0);
	}

	/*