NetBSD/sys/filecorefs/filecore_lookup.c

/*	$NetBSD: filecore_lookup.c,v 1.2 1998/08/14 18:04:05 mark Exp $	*/

/*-
 * Copyright (c) 1998 Andrew McMurry
 * Copyright (c) 1989, 1993, 1994 The Regents of the University of California.
 * All rights reserved.
 *
 * 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.
 *
 *	filecore_lookup.c	1.1	1998/6/26
 */

#include <sys/param.h>
#include <sys/namei.h>
#include <sys/buf.h>
#include <sys/file.h>
#include <sys/vnode.h>
#include <sys/mount.h>
#include <sys/systm.h>

#include <filecorefs/filecore.h>
#include <filecorefs/filecore_extern.h>
#include <filecorefs/filecore_node.h>

struct	nchstats filecore_nchstats;

/*
 * Convert a component of a pathname into a pointer to a locked inode.
 * This is a very central and rather complicated routine.
 * If the file system is not maintained in a strict tree hierarchy,
 * this can result in a deadlock situation (see comments in code below).
 *
 * The flag argument is LOOKUP, CREATE, RENAME, or DELETE depending on
 * whether the name is to be looked up, created, renamed, or deleted.
 * When CREATE, RENAME, or DELETE is specified, information usable in
 * creating, renaming, or deleting a directory entry may be calculated.
 * If flag has LOCKPARENT or'ed into it and the target of the pathname
 * exists, lookup returns both the target and its parent directory locked.
 * When creating or renaming and LOCKPARENT is specified, the target may
 * not be ".".  When deleting and LOCKPARENT is specified, the target may
 * be "."., but the caller must check to ensure it does an vrele and iput
 * instead of two iputs.
 *
 * Overall outline of ufs_lookup:
 *
 *	check accessibility of directory
 *	look for name in cache, if found, then if at end of path
 *	  and deleting or creating, drop it, else return name
 *	search for name in directory, to found or notfound
 * notfound:
 *	if creating, return locked directory, leaving info on available slots
 *	else return error
 * found:
 *	if at end of path and deleting, return information to allow delete
 *	if at end of path and rewriting (RENAME and LOCKPARENT), lock target
 *	  inode and return info to allow rewrite
 *	if not at end, add name to cache; if at end and neither creating
 *	  nor deleting, add name to cache
 *
 * NOTE: (LOOKUP | LOCKPARENT) currently returns the parent inode unlocked.
 */
int
filecore_lookup(v)
	void *v;
{
	struct vop_lookup_args /* {
		struct vnode *a_dvp;
		struct vnode **a_vpp;
		struct componentname *a_cnp;
	} */ *ap = v;
	struct vnode *vdp;		/* vnode for directory being searched */
	struct filecore_node *dp;	/* inode for directory being searched */
	struct filecore_mnt *fcmp;	/* file system that directory is in */
	struct buf *bp;			/* a buffer of directory entries */
	struct filecore_direntry *de;
	int numdirpasses;		/* strategy for directory search */
	struct vnode *pdp;		/* saved dp during symlink work */
	struct vnode *tdp;		/* returned by filecore_vget_internal */
	int lockparent;			/* 1 => lockparent flag is set */
	int wantparent;			/* 1 => wantparent or lockparent flag */
	int error;
	u_short namelen;
	int res;
	const char *name;
	struct vnode **vpp = ap->a_vpp;
	struct componentname *cnp = ap->a_cnp;
	struct ucred *cred = cnp->cn_cred;
	int flags = cnp->cn_flags;
	int nameiop = cnp->cn_nameiop;
	int i, endsearch;
	
	bp = NULL;
	*vpp = NULL;
	vdp = ap->a_dvp;
	dp = VTOI(vdp);
	fcmp = dp->i_mnt;
	lockparent = flags & LOCKPARENT;
	wantparent = flags & (LOCKPARENT|WANTPARENT);
	
	/*
	 * Check accessiblity of directory.
	 */
	if ((error = VOP_ACCESS(vdp, VEXEC, cred, cnp->cn_proc)) != 0)
		return (error);

	if ((flags & ISLASTCN) && (vdp->v_mount->mnt_flag & MNT_RDONLY) &&
	    (cnp->cn_nameiop == DELETE || cnp->cn_nameiop == RENAME))
		return (EROFS);

	/*
	 * We now have a segment name to search for, and a directory to search.
	 *
	 * Before tediously performing a linear scan of the directory,
	 * check the name cache to see if the directory/name pair
	 * we are looking for is known already.
	 */
	if ((error = cache_lookup(vdp, vpp, cnp)) != 0) {
		int vpid;	/* capability number of vnode */

		if (error == ENOENT)
			return (error);
#ifdef PARANOID
		if ((vdp->v_flag & VROOT) && (flags & ISDOTDOT))
			panic("filecore_lookup: .. through root");
#endif
		/*
		 * Get the next vnode in the path.
		 * See comment below starting `Step through' for
		 * an explaination of the locking protocol.
		 */
		pdp = vdp;
		dp = VTOI(*vpp);
		vdp = *vpp;
		vpid = vdp->v_id;
		if (pdp == vdp) {
			VREF(vdp);
			error = 0;
		} else if (flags & ISDOTDOT) {
			VOP_UNLOCK(pdp, 0);
			error = vget(vdp, LK_EXCLUSIVE);
			if (!error && lockparent && (flags & ISLASTCN))
				error = vn_lock(pdp, LK_EXCLUSIVE);
		} else {
			error = vget(vdp, LK_EXCLUSIVE);
			if (!lockparent || error || !(flags & ISLASTCN))
				VOP_UNLOCK(pdp, 0);
		}
		/*
		 * Check that the capability number did not change
		 * while we were waiting for the lock.
		 */
		if (!error) {
			if (vpid == vdp->v_id)
				return (0);
			vput(vdp);
			if (lockparent && pdp != vdp && (flags & ISLASTCN))
				VOP_UNLOCK(pdp, 0);
		}
		if ((error = vn_lock(pdp, LK_EXCLUSIVE)) != 0)
			return (error);
		vdp = pdp;
		dp = VTOI(pdp);
		*vpp = NULL;
	}
	
	name = cnp->cn_nameptr;
	namelen = cnp->cn_namelen;
	
	/*
	 * If there is cached information on a previous search of
	 * this directory, pick up where we last left off.
	 * We cache only lookups as these are the most common
	 * and have the greatest payoff. Caching CREATE has little
	 * benefit as it usually must search the entire directory
	 * to determine that the entry does not exist. Caching the
	 * location of the last DELETE or RENAME has not reduced
	 * profiling time and hence has been removed in the interest
	 * of simplicity.
	 */
	if (nameiop != LOOKUP || dp->i_diroff == 0 ||
	    dp->i_diroff >= FILECORE_MAXDIRENTS) {
		i = 0;
		numdirpasses = 1;
	} else {
		i = dp->i_diroff;
		numdirpasses = 2;
		filecore_nchstats.ncs_2passes++;
	}
	endsearch = FILECORE_MAXDIRENTS;

	if ((flags & ISDOTDOT) || (name[0] == '.' && namelen == 1))
		goto found;

	error = filecore_dbread(dp, &bp);
	if (error)
		return error;

	de = fcdirentry(bp->b_data, i);
	
searchloop:
	while (de->name[0] != 0 && i < endsearch) {
		/*
		 * Check for a name match.
		 */
		res = filecore_fncmp(de->name, name, namelen);

		if (res == 0)
			goto found;
		if (res < 0)
			goto notfound;

		i++;
		de++;
	}

notfound:
	/*
	 * If we started in the middle of the directory and failed
	 * to find our target, we must check the beginning as well.
	 */
	if (numdirpasses == 2) {
		numdirpasses--;
		i = 0;
		de = fcdirentry(bp->b_data, i);
		endsearch = dp->i_diroff;
		goto searchloop;
	}
	if (bp != NULL) {
#ifdef FILECORE_DEBUG_BR
			printf("brelse(%p) lo1\n", bp);
#endif
		brelse(bp);
	}

	/*
	 * Insert name into cache (as non-existent) if appropriate.
	 */
	if (cnp->cn_flags & MAKEENTRY)
		cache_enter(vdp, *vpp, cnp);
	if (nameiop == CREATE || nameiop == RENAME)
		return (EJUSTRETURN);
	return (ENOENT);
	
found:
	if (numdirpasses == 2)
		filecore_nchstats.ncs_pass2++;
	
	/*
	 * Found component in pathname.
	 * If the final component of path name, save information
	 * in the cache as to where the entry was found.
	 */
	if ((flags & ISLASTCN) && nameiop == LOOKUP)
		dp->i_diroff = i;
	
	/*
	 * Step through the translation in the name.  We do not `iput' the
	 * directory because we may need it again if a symbolic link
	 * is relative to the current directory.  Instead we save it
	 * unlocked as "pdp".  We must get the target inode before unlocking
	 * the directory to insure that the inode will not be removed
	 * before we get it.  We prevent deadlock by always fetching
	 * inodes from the root, moving down the directory tree. Thus
	 * when following backward pointers ".." we must unlock the
	 * parent directory before getting the requested directory.
	 * There is a potential race condition here if both the current
	 * and parent directories are removed before the `iget' for the
	 * inode associated with ".." returns.  We hope that this occurs
	 * infrequently since we cannot avoid this race condition without
	 * implementing a sophisticated deadlock detection algorithm.
	 * Note also that this simple deadlock detection scheme will not
	 * work if the file system has any hard links other than ".."
	 * that point backwards in the directory structure.
	 */
	pdp = vdp;
	/*
	 * If ino is different from dp->i_ino,
	 * it's a relocated directory.
	 */
	if (flags & ISDOTDOT) {
		ino_t pin = filecore_getparent(dp);
		VOP_UNLOCK(pdp, 0);	/* race to get the inode */
		error = VFS_VGET(vdp->v_mount, pin, &tdp);
		if (error) {
			vn_lock(pdp, LK_EXCLUSIVE | LK_RETRY);
			return (error);
		}
		if (lockparent && (flags & ISLASTCN) &&
		    (error = vn_lock(pdp, LK_EXCLUSIVE))) {
			vput(tdp);
			return (error);
		}
		*vpp = tdp;
	} else if (name[0] == '.' && namelen == 1) {
		VREF(vdp);	/* we want ourself, ie "." */
		*vpp = vdp;
	} else {
#ifdef FILECORE_DEBUG_BR
			printf("brelse(%p) lo4\n", bp);
#endif
		brelse(bp);
		error = VFS_VGET(vdp->v_mount, dp->i_dirent.addr |
		    (i << FILECORE_INO_INDEX), &tdp);
		if (error)
			return (error);
		if (!lockparent || !(flags & ISLASTCN))
			VOP_UNLOCK(pdp, 0);
		*vpp = tdp;
	}
	
	/*
	 * Insert name into cache if appropriate.
	 */
	if (cnp->cn_flags & MAKEENTRY)
		cache_enter(vdp, *vpp, cnp);
	return (0);
}