xref: /openbsd-current/sys/ufs/ufs/ufs_lookup.c

/*	$OpenBSD: ufs_lookup.c,v 1.61 2024/02/03 18:51:58 beck Exp $	*/
/*	$NetBSD: ufs_lookup.c,v 1.7 1996/02/09 22:36:06 christos Exp $	*/

/*
 * Copyright (c) 1989, 1993
 *	The Regents of the University of California.  All rights reserved.
 * (c) UNIX System Laboratories, Inc.
 * All or some portions of this file are derived from material licensed
 * to the University of California by American Telephone and Telegraph
 * Co. or Unix System Laboratories, Inc. and are reproduced herein with
 * the permission of UNIX System Laboratories, Inc.
 *
 * 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. 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.
 *
 *	@(#)ufs_lookup.c	8.9 (Berkeley) 8/11/94
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/namei.h>
#include <sys/buf.h>
#include <sys/stat.h>
#include <sys/mount.h>
#include <sys/proc.h>
#include <sys/vnode.h>

#include <ufs/ufs/quota.h>
#include <ufs/ufs/inode.h>
#include <ufs/ufs/dir.h>
#ifdef UFS_DIRHASH
#include <ufs/ufs/dirhash.h>
#endif
#include <ufs/ufs/ufsmount.h>
#include <ufs/ufs/ufs_extern.h>

extern	struct nchstats nchstats;

#ifdef DIAGNOSTIC
int	dirchk = 1;
#else
int	dirchk = 0;
#endif

/*
 * 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 cnp->cn_nameiop 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 vput
 * instead of two vputs.
 *
 * 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
 */
int
ufs_lookup(void *v)
{
	struct vop_lookup_args *ap = v;
	struct vnode *vdp;		/* vnode for directory being searched */
	struct inode *dp;		/* inode for directory being searched */
	struct buf *bp;			/* a buffer of directory entries */
	struct direct *ep;		/* the current directory entry */
	int entryoffsetinblock;		/* offset of ep in bp's buffer */
	enum {NONE, COMPACT, FOUND} slotstatus;
	doff_t slotoffset;		/* offset of area with free space */
	int slotsize;			/* size of area at slotoffset */
	int slotfreespace;		/* amount of space free in slot */
	int slotneeded;			/* size of the entry we're seeking */
	int numdirpasses;		/* strategy for directory search */
	doff_t endsearch;		/* offset to end directory search */
	doff_t prevoff;			/* prev entry dp->i_offset */
	struct vnode *pdp;		/* saved dp during symlink work */
	struct vnode *tdp;		/* returned by VFS_VGET */
	doff_t enduseful;		/* pointer past last used dir slot */
	u_long bmask;			/* block offset mask */
	int lockparent;			/* 1 => lockparent flag is set */
	int wantparent;			/* 1 => wantparent or lockparent flag */
	int namlen, error;
	struct vnode **vpp = ap->a_vpp;
	struct componentname *cnp = ap->a_cnp;
	struct ucred *cred = cnp->cn_cred;
	int flags;
	int nameiop = cnp->cn_nameiop;

	cnp->cn_flags &= ~PDIRUNLOCK;
	flags = cnp->cn_flags;

	bp = NULL;
	slotoffset = -1;
	*vpp = NULL;
	vdp = ap->a_dvp;
	dp = VTOI(vdp);
	lockparent = flags & LOCKPARENT;
	wantparent = flags & (LOCKPARENT|WANTPARENT);

	/*
	 * Check accessibility of directory.
	 */
	if ((DIP(dp, mode) & IFMT) != IFDIR)
		return (ENOTDIR);
	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)
		return (error);

	/*
	 * Suppress search for slots unless creating
	 * file and at end of pathname, in which case
	 * we watch for a place to put the new file in
	 * case it doesn't already exist.
	 */
	slotstatus = FOUND;
	slotfreespace = slotsize = slotneeded = 0;
	if ((nameiop == CREATE || nameiop == RENAME) &&
	    (flags & ISLASTCN)) {
		slotstatus = NONE;
		slotneeded = (sizeof(struct direct) - MAXNAMLEN +
			cnp->cn_namelen + 3) &~ 3;
	}

	/*
	 * 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.
	 */
	bmask = VFSTOUFS(vdp->v_mount)->um_mountp->mnt_stat.f_iosize - 1;

#ifdef UFS_DIRHASH
	/*
	 * Use dirhash for fast operations on large directories. The logic
	 * to determine whether to hash the directory is contained within
	 * ufsdirhash_build(); a zero return means that it decided to hash
	 * this directory and it successfully built up the hash table.
	 */
	if (ufsdirhash_build(dp) == 0) {
		/* Look for a free slot if needed. */
		enduseful = DIP(dp, size);
		if (slotstatus != FOUND) {
			slotoffset = ufsdirhash_findfree(dp, slotneeded,
			    &slotsize);
			if (slotoffset >= 0) {
				slotstatus = COMPACT;
				enduseful = ufsdirhash_enduseful(dp);
				if (enduseful < 0)
					enduseful = DIP(dp, size);
			}
		}
		/* Look up the component. */
		numdirpasses = 1;
		entryoffsetinblock = 0; /* silence compiler warning */
		switch (ufsdirhash_lookup(dp, cnp->cn_nameptr, cnp->cn_namelen,
		    &dp->i_offset, &bp, nameiop == DELETE ? &prevoff : NULL)) {
		case 0:
			ep = (struct direct *)((char *)bp->b_data +
			    (dp->i_offset & bmask));
			goto foundentry;
		case ENOENT:
#define roundup2(x, y)	(((x)+((y)-1))&(~((y)-1))) /* if y is powers of two */
			dp->i_offset = roundup2(DIP(dp, size), DIRBLKSIZ);
			goto notfound;
		default:
			/* Something failed; just do a linear search. */
			break;
		}
	}
#endif /* UFS_DIRHASH */

	if (nameiop != LOOKUP || dp->i_diroff == 0 ||
	    dp->i_diroff >= DIP(dp, size)) {
		entryoffsetinblock = 0;
		dp->i_offset = 0;
		numdirpasses = 1;
	} else {
		dp->i_offset = dp->i_diroff;
		if ((entryoffsetinblock = dp->i_offset & bmask) &&
		    (error = UFS_BUFATOFF(dp, (off_t)dp->i_offset, NULL, &bp)))
			return (error);
		numdirpasses = 2;
		nchstats.ncs_2passes++;
	}
	prevoff = dp->i_offset;
	endsearch = roundup(DIP(dp, size), DIRBLKSIZ);
	enduseful = 0;

searchloop:
	while (dp->i_offset < endsearch) {
		/*
		 * If necessary, get the next directory block.
		 */
		if ((dp->i_offset & bmask) == 0) {
			if (bp != NULL)
				brelse(bp);
			error = UFS_BUFATOFF(dp, (off_t)dp->i_offset, NULL,
					     &bp);
			if (error)
				return (error);
			entryoffsetinblock = 0;
		}
		/*
		 * If still looking for a slot, and at a DIRBLKSIZE
		 * boundary, have to start looking for free space again.
		 */
		if (slotstatus == NONE &&
		    (entryoffsetinblock & (DIRBLKSIZ - 1)) == 0) {
			slotoffset = -1;
			slotfreespace = 0;
		}
		/*
		 * Get pointer to next entry.
		 * Full validation checks are slow, so we only check
		 * enough to insure forward progress through the
		 * directory. Complete checks can be run by patching
		 * "dirchk" to be true.
		 */
		ep = (struct direct *)((char *)bp->b_data + entryoffsetinblock);
		if (ep->d_reclen == 0 ||
		    (dirchk && ufs_dirbadentry(vdp, ep, entryoffsetinblock))) {
			int i;

			ufs_dirbad(dp, dp->i_offset, "mangled entry");
			i = DIRBLKSIZ - (entryoffsetinblock & (DIRBLKSIZ - 1));
			dp->i_offset += i;
			entryoffsetinblock += i;
			continue;
		}

		/*
		 * If an appropriate sized slot has not yet been found,
		 * check to see if one is available. Also accumulate space
		 * in the current block so that we can determine if
		 * compaction is viable.
		 */
		if (slotstatus != FOUND) {
			int size = ep->d_reclen;

			if (ep->d_ino != 0)
				size -= DIRSIZ(ep);
			if (size > 0) {
				if (size >= slotneeded) {
					slotstatus = FOUND;
					slotoffset = dp->i_offset;
					slotsize = ep->d_reclen;
				} else if (slotstatus == NONE) {
					slotfreespace += size;
					if (slotoffset == -1)
						slotoffset = dp->i_offset;
					if (slotfreespace >= slotneeded) {
						slotstatus = COMPACT;
						slotsize = dp->i_offset +
						      ep->d_reclen - slotoffset;
					}
				}
			}
		}

		/*
		 * Check for a name match.
		 */
		if (ep->d_ino) {
			namlen = ep->d_namlen;
			if (namlen == cnp->cn_namelen &&
			    !memcmp(cnp->cn_nameptr, ep->d_name, namlen)) {
#ifdef UFS_DIRHASH
foundentry:
#endif
				/*
				 * Save directory entry's inode number and
				 * reclen in ndp->ni_ufs area, and release
				 * directory buffer.
				 */
				dp->i_ino = ep->d_ino;
				dp->i_reclen = ep->d_reclen;
				goto found;
			}
		}
		prevoff = dp->i_offset;
		dp->i_offset += ep->d_reclen;
		entryoffsetinblock += ep->d_reclen;
		if (ep->d_ino)
			enduseful = dp->i_offset;
	}
#ifdef UFS_DIRHASH
notfound:
#endif
	/*
	 * 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--;
		dp->i_offset = 0;
		endsearch = dp->i_diroff;
		goto searchloop;
	}
	if (bp != NULL)
		brelse(bp);
	/*
	 * If creating, and at end of pathname and current
	 * directory has not been removed, then can consider
	 * allowing file to be created.
	 */
	if ((nameiop == CREATE || nameiop == RENAME) &&
	    (flags & ISLASTCN) && dp->i_effnlink != 0) {
		/*
		 * Access for write is interpreted as allowing
		 * creation of files in the directory.
		 */
		error = VOP_ACCESS(vdp, VWRITE, cred, cnp->cn_proc);
		if (error)
			return (error);
		/*
		 * Return an indication of where the new directory
		 * entry should be put.  If we didn't find a slot,
		 * then set dp->i_count to 0 indicating
		 * that the new slot belongs at the end of the
		 * directory. If we found a slot, then the new entry
		 * can be put in the range from dp->i_offset to
		 * dp->i_offset + dp->i_count.
		 */
		if (slotstatus == NONE) {
			dp->i_offset = roundup(DIP(dp, size), DIRBLKSIZ);
			dp->i_count = 0;
			enduseful = dp->i_offset;
		} else if (nameiop == DELETE) {
			dp->i_offset = slotoffset;
			if ((dp->i_offset & (DIRBLKSIZ - 1)) == 0)
				dp->i_count = 0;
			else
				dp->i_count = dp->i_offset - prevoff;
		} else {
			dp->i_offset = slotoffset;
			dp->i_count = slotsize;
			if (enduseful < slotoffset + slotsize)
				enduseful = slotoffset + slotsize;
		}
		dp->i_endoff = roundup(enduseful, DIRBLKSIZ);
		/*
		 * We return with the directory locked, so that
		 * the parameters we set up above will still be
		 * valid if we actually decide to do a direnter().
		 * We return ni_vp == NULL to indicate that the entry
		 * does not currently exist; we leave a pointer to
		 * the (locked) directory inode in ndp->ni_dvp.
		 * The pathname buffer is saved so that the name
		 * can be obtained later.
		 *
		 * NB - if the directory is unlocked, then this
		 * information cannot be used.
		 */
		cnp->cn_flags |= SAVENAME;
		if (!lockparent) {
			VOP_UNLOCK(vdp);
			cnp->cn_flags |= PDIRUNLOCK;
		}
		return (EJUSTRETURN);
	}
	/*
	 * Insert name into cache (as non-existent) if appropriate.
	 */
	if ((cnp->cn_flags & MAKEENTRY) && nameiop != CREATE)
		cache_enter(vdp, *vpp, cnp);
	return (ENOENT);

found:
	if (numdirpasses == 2)
		nchstats.ncs_pass2++;
	/*
	 * Check that directory length properly reflects presence
	 * of this entry.
	 */
	if (dp->i_offset + DIRSIZ(ep) > DIP(dp, size)) {
		ufs_dirbad(dp, dp->i_offset, "i_ffs_size too small");
		DIP_ASSIGN(dp, size, dp->i_offset + DIRSIZ(ep));
		dp->i_flag |= IN_CHANGE | IN_UPDATE;
	}
	brelse(bp);

	/*
	 * 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 = dp->i_offset &~ (DIRBLKSIZ - 1);

	/*
	 * If deleting, and at end of pathname, return
	 * parameters which can be used to remove file.
	 * If the wantparent flag isn't set, we return only
	 * the directory (in ndp->ni_dvp), otherwise we go
	 * on and lock the inode, being careful with ".".
	 */
	if (nameiop == DELETE && (flags & ISLASTCN)) {
		/*
		 * Write access to directory required to delete files.
		 */
		error = VOP_ACCESS(vdp, VWRITE, cred, cnp->cn_proc);
		if (error)
			return (error);
		/*
		 * Return pointer to current entry in dp->i_offset,
		 * and distance past previous entry (if there
		 * is a previous entry in this block) in dp->i_count.
		 * Save directory inode pointer in ndp->ni_dvp for dirremove().
		 */
		if ((dp->i_offset & (DIRBLKSIZ - 1)) == 0)
			dp->i_count = 0;
		else
			dp->i_count = dp->i_offset - prevoff;
		if (dp->i_number == dp->i_ino) {
			vref(vdp);
			*vpp = vdp;
			return (0);
		}
		error = VFS_VGET(vdp->v_mount, dp->i_ino, &tdp);
		if (error)
			return (error);
		/*
		 * If directory is "sticky", then user must own
		 * the directory, or the file in it, else she
		 * may not delete it (unless she's root). This
		 * implements append-only directories.
		 */
		if ((DIP(dp, mode) & ISVTX) &&
		    cred->cr_uid != 0 &&
		    cred->cr_uid != DIP(dp, uid) &&
		    !vnoperm(vdp) &&
		    DIP(VTOI(tdp), uid) != cred->cr_uid) {
			vput(tdp);
			return (EPERM);
		}
		*vpp = tdp;
		if (!lockparent) {
			VOP_UNLOCK(vdp);
			cnp->cn_flags |= PDIRUNLOCK;
		}
		return (0);
	}

	/*
	 * If rewriting (RENAME), return the inode and the
	 * information required to rewrite the present directory
	 * Must get inode of directory entry to verify it's a
	 * regular file, or empty directory.
	 */
	if (nameiop == RENAME && wantparent &&
	    (flags & ISLASTCN)) {
		error = VOP_ACCESS(vdp, VWRITE, cred, cnp->cn_proc);
		if (error)
			return (error);
		/*
		 * Careful about locking second inode.
		 * This can only occur if the target is ".".
		 */
		if (dp->i_number == dp->i_ino)
			return (EISDIR);
		error = VFS_VGET(vdp->v_mount, dp->i_ino, &tdp);
		if (error)
			return (error);
		*vpp = tdp;
		cnp->cn_flags |= SAVENAME;
		if (!lockparent) {
			VOP_UNLOCK(vdp);
			cnp->cn_flags |= PDIRUNLOCK;
		}
		return (0);
	}

	/*
	 * Step through the translation in the name.  We do not `vput' 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 VFS_VGET 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 (flags & ISDOTDOT) {
		VOP_UNLOCK(pdp);	/* race to get the inode */
		cnp->cn_flags |= PDIRUNLOCK;
		error = VFS_VGET(vdp->v_mount, dp->i_ino, &tdp);
		if (error) {
			if (vn_lock(pdp, LK_EXCLUSIVE | LK_RETRY) == 0)
				cnp->cn_flags &= ~PDIRUNLOCK;
			return (error);
		}
		if (lockparent && (flags & ISLASTCN)) {
			if ((error = vn_lock(pdp, LK_EXCLUSIVE))) {
				vput(tdp);
				return (error);
			}
			cnp->cn_flags &= ~PDIRUNLOCK;
		}
		*vpp = tdp;
	} else if (dp->i_number == dp->i_ino) {
		vref(vdp);	/* we want ourself, ie "." */
		*vpp = vdp;
	} else {
		error = VFS_VGET(vdp->v_mount, dp->i_ino, &tdp);
		if (error)
			return (error);
		if (!lockparent || !(flags & ISLASTCN)) {
			VOP_UNLOCK(pdp);
			cnp->cn_flags |= PDIRUNLOCK;
		}
		*vpp = tdp;
	}

	/*
	 * Insert name into cache if appropriate.
	 */
	if (cnp->cn_flags & MAKEENTRY)
		cache_enter(vdp, *vpp, cnp);
	return (0);
}

void
ufs_dirbad(struct inode *ip, doff_t offset, char *how)
{
	struct mount *mp;

	mp = ITOV(ip)->v_mount;
	(void)printf("%s: bad dir ino %u at offset %d: %s\n",
	    mp->mnt_stat.f_mntonname, ip->i_number, offset, how);
	if ((mp->mnt_stat.f_flags & MNT_RDONLY) == 0)
		panic("bad dir");
}

/*
 * Do consistency checking on a directory entry:
 *	record length must be multiple of 4
 *	entry must fit in rest of its DIRBLKSIZ block
 *	record must be large enough to contain entry
 *	name is not longer than MAXNAMLEN
 *	name must be as long as advertised, and null terminated
 */
int
ufs_dirbadentry(struct vnode *vdp, struct direct *ep, int entryoffsetinblock)
{
	struct inode *dp;
	int i;
	int namlen;

	dp = VTOI(vdp);

	namlen = ep->d_namlen;
	if ((ep->d_reclen & 0x3) != 0 ||
	    ep->d_reclen > DIRBLKSIZ - (entryoffsetinblock & (DIRBLKSIZ - 1)) ||
	    ep->d_reclen < DIRSIZ(ep) || namlen > MAXNAMLEN) {
		/*return (1); */
		printf("First bad\n");
		goto bad;
	}
	if (ep->d_ino == 0)
		return (0);
	for (i = 0; i < namlen; i++)
		if (ep->d_name[i] == '\0') {
			/*return (1); */
			printf("Second bad\n");
			goto bad;
	}
	if (ep->d_name[i])
		goto bad;
	return (0);
bad:
	return (1);
}

/*
 * Construct a new directory entry after a call to namei, using the
 * parameters that it left in the componentname argument cnp. The
 * argument ip is the inode to which the new directory entry will refer.
 */
void
ufs_makedirentry(struct inode *ip, struct componentname *cnp,
    struct direct *newdirp)
{
#ifdef DIAGNOSTIC
  	if ((cnp->cn_flags & SAVENAME) == 0)
		panic("ufs_makedirentry: missing name");
#endif
	newdirp->d_ino = ip->i_number;
	newdirp->d_namlen = cnp->cn_namelen;
	memset(newdirp->d_name + (cnp->cn_namelen & ~(DIR_ROUNDUP-1)),
	    0, DIR_ROUNDUP);
	memcpy(newdirp->d_name, cnp->cn_nameptr, cnp->cn_namelen);
	newdirp->d_type = IFTODT(DIP(ip, mode));
}

/*
 * Write a directory entry after a call to namei, using the parameters
 * that it left in nameidata. The argument dirp is the new directory
 * entry contents. Dvp is a pointer to the directory to be written,
 * which was left locked by namei. Remaining parameters (dp->i_offset,
 * dp->i_count) indicate how the space for the new entry is to be obtained.
 * Non-null bp indicates that a directory is being created (for the
 * soft dependency code).
 */
int
ufs_direnter(struct vnode *dvp, struct vnode *tvp, struct direct *dirp,
    struct componentname *cnp, struct buf *newdirbp)
{
	struct ucred *cr;
	struct proc *p;
	int newentrysize;
	struct inode *dp;
	struct buf *bp;
	u_int dsize;
	struct direct *ep, *nep;
	int error, ret, blkoff, loc, spacefree, flags;
	char *dirbuf;

	error = 0;
	cr = cnp->cn_cred;
	p = cnp->cn_proc;
	dp = VTOI(dvp);
	newentrysize = DIRSIZ(dirp);

	if (dp->i_count == 0) {
		/*
		 * If dp->i_count is 0, then namei could find no
		 * space in the directory. Here, dp->i_offset will
		 * be on a directory block boundary and we will write the
		 * new entry into a fresh block.
		 */
		if (dp->i_offset & (DIRBLKSIZ - 1))
			panic("ufs_direnter: newblk");
		flags = B_CLRBUF;
		flags |= B_SYNC;
		if ((error = UFS_BUF_ALLOC(dp, (off_t)dp->i_offset, DIRBLKSIZ,
		    cr, flags, &bp)) != 0) {
			return (error);
		}
		DIP_ASSIGN(dp, size, dp->i_offset + DIRBLKSIZ);
		dp->i_flag |= IN_CHANGE | IN_UPDATE;
		uvm_vnp_setsize(dvp, DIP(dp, size));
		dirp->d_reclen = DIRBLKSIZ;
		blkoff = dp->i_offset &
		    (VFSTOUFS(dvp->v_mount)->um_mountp->mnt_stat.f_iosize - 1);
		memcpy(bp->b_data + blkoff, dirp, newentrysize);

#ifdef UFS_DIRHASH
		if (dp->i_dirhash != NULL) {
			ufsdirhash_newblk(dp, dp->i_offset);
			ufsdirhash_add(dp, dirp, dp->i_offset);
			ufsdirhash_checkblock(dp, (char *)bp->b_data + blkoff,
			dp->i_offset);
		}
#endif

		error = VOP_BWRITE(bp);
		ret = UFS_UPDATE(dp, 1);
		if (error == 0)
			return (ret);
		return (error);
	}

	/*
	 * If dp->i_count is non-zero, then namei found space for the new
	 * entry in the range dp->i_offset to dp->i_offset + dp->i_count
	 * in the directory. To use this space, we may have to compact
	 * the entries located there, by copying them together towards the
	 * beginning of the block, leaving the free space in one usable
	 * chunk at the end.
	 */

	/*
	 * Increase size of directory if entry eats into new space.
	 * This should never push the size past a new multiple of
	 * DIRBLKSIZE.
	 *
	 * N.B. - THIS IS AN ARTIFACT OF 4.2 AND SHOULD NEVER HAPPEN.
	 */
	if (dp->i_offset + dp->i_count > DIP(dp, size))
		DIP_ASSIGN(dp, size, dp->i_offset + dp->i_count);
	/*
	 * Get the block containing the space for the new directory entry.
	 */
	if ((error = UFS_BUFATOFF(dp, (off_t)dp->i_offset, &dirbuf, &bp))
	    != 0) {
		return (error);
	}
	/*
	 * Find space for the new entry. In the simple case, the entry at
	 * offset base will have the space. If it does not, then namei
	 * arranged that compacting the region dp->i_offset to
	 * dp->i_offset + dp->i_count would yield the space.
	 */
	ep = (struct direct *)dirbuf;
	dsize = ep->d_ino ? DIRSIZ(ep) : 0;
	spacefree = ep->d_reclen - dsize;
	for (loc = ep->d_reclen; loc < dp->i_count; ) {
		nep = (struct direct *)(dirbuf + loc);

		/* Trim the existing slot (NB: dsize may be zero). */
		ep->d_reclen = dsize;
		ep = (struct direct *)((char *)ep + dsize);

		/* Read nep->d_reclen now as the memmove() may clobber it. */
		loc += nep->d_reclen;
		if (nep->d_ino == 0) {
			/*
			 * A mid-block unused entry. Such entries are
			 * never created by the kernel, but fsck_ffs
			 * can create them (and it doesn't fix them).
			 *
			 * Add up the free space, and initialise the
			 * relocated entry since we don't memmove it.
			 */
			spacefree += nep->d_reclen;
			ep->d_ino = 0;
			dsize = 0;
			continue;
		}
		dsize = DIRSIZ(nep);
		spacefree += nep->d_reclen - dsize;
#ifdef UFS_DIRHASH
		if (dp->i_dirhash != NULL)
			ufsdirhash_move(dp, nep,
			    dp->i_offset + ((char *)nep - dirbuf),
			    dp->i_offset + ((char *)ep - dirbuf));
#endif
		memmove(ep, nep, dsize);
	}
	/*
	 * Here, `ep' points to a directory entry containing `dsize' in-use
	 * bytes followed by `spacefree' unused bytes. If ep->d_ino == 0,
	 * then the entry is completely unused (dsize == 0). The value
	 * of ep->d_reclen is always indeterminate.
	 *
	 * Update the pointer fields in the previous entry (if any),
	 * copy in the new entry, and write out the block.
	 */
	if (ep->d_ino == 0) {
		if (spacefree + dsize < newentrysize)
			panic("ufs_direnter: compact1");
		dirp->d_reclen = spacefree + dsize;
	} else {
		if (spacefree < newentrysize)
			panic("ufs_direnter: compact2");
		dirp->d_reclen = spacefree;
		ep->d_reclen = dsize;
		ep = (struct direct *)((char *)ep + dsize);
	}

#ifdef UFS_DIRHASH
	if (dp->i_dirhash != NULL && (ep->d_ino == 0 ||
	    dirp->d_reclen == spacefree))
		ufsdirhash_add(dp, dirp, dp->i_offset + ((char *)ep - dirbuf));
#endif
	memcpy(ep, dirp, newentrysize);
#ifdef UFS_DIRHASH
	if (dp->i_dirhash != NULL)
		ufsdirhash_checkblock(dp, dirbuf -
		    (dp->i_offset & (DIRBLKSIZ - 1)),
		    dp->i_offset & ~(DIRBLKSIZ - 1));
#endif

	error = VOP_BWRITE(bp);
	dp->i_flag |= IN_CHANGE | IN_UPDATE;

	/*
	 * If all went well, and the directory can be shortened, proceed
	 * with the truncation. Note that we have to unlock the inode for
	 * the entry that we just entered, as the truncation may need to
	 * lock other inodes which can lead to deadlock if we also hold a
	 * lock on the newly entered node.
	 */

	if (error == 0 && dp->i_endoff && dp->i_endoff < DIP(dp, size)) {
		if (tvp != NULL)
			VOP_UNLOCK(tvp);
		error = UFS_TRUNCATE(dp, (off_t)dp->i_endoff, IO_SYNC, cr);
#ifdef UFS_DIRHASH
		if (error == 0 && dp->i_dirhash != NULL)
			ufsdirhash_dirtrunc(dp, dp->i_endoff);
#endif
		if (tvp != NULL)
			vn_lock(tvp, LK_EXCLUSIVE | LK_RETRY);
	}
	return (error);
}

/*
 * Remove a directory entry after a call to namei, using
 * the parameters which it left in nameidata. The entry
 * dp->i_offset contains the offset into the directory of the
 * entry to be eliminated.  The dp->i_count field contains the
 * size of the previous record in the directory.  If this
 * is 0, the first entry is being deleted, so we need only
 * zero the inode number to mark the entry as free.  If the
 * entry is not the first in the directory, we must reclaim
 * the space of the now empty record by adding the record size
 * to the size of the previous entry.
 */
int
ufs_dirremove(struct vnode *dvp, struct inode *ip, int flags, int isrmdir)
{
	struct inode *dp;
	struct direct *ep;
	struct buf *bp;
	int error;

	dp = VTOI(dvp);

	if ((error = UFS_BUFATOFF(dp,
	    (off_t)(dp->i_offset - dp->i_count), (char **)&ep, &bp)) != 0)
		return (error);
#ifdef UFS_DIRHASH
	/*
	 * Remove the dirhash entry. This is complicated by the fact
	 * that `ep' is the previous entry when dp->i_count != 0.
	 */
	if (dp->i_dirhash != NULL)
		ufsdirhash_remove(dp, (dp->i_count == 0) ? ep :
		(struct direct *)((char *)ep + ep->d_reclen), dp->i_offset);
#endif

	if (dp->i_count == 0) {
		/*
		 * First entry in block: set d_ino to zero.
		 */
		ep->d_ino = 0;
	} else {
		/*
		 * Collapse new free space into previous entry.
		 */
		ep->d_reclen += dp->i_reclen;
	}
#ifdef UFS_DIRHASH
	if (dp->i_dirhash != NULL)
		ufsdirhash_checkblock(dp, (char *)ep -
		    ((dp->i_offset - dp->i_count) & (DIRBLKSIZ - 1)),
		    dp->i_offset & ~(DIRBLKSIZ - 1));
#endif
	if (ip) {
		ip->i_effnlink--;
		DIP_ADD(ip, nlink, -1);
		ip->i_flag |= IN_CHANGE;
	}
	if (DOINGASYNC(dvp) && dp->i_count != 0) {
		bdwrite(bp);
		error = 0;
	} else
		error = bwrite(bp);

	dp->i_flag |= IN_CHANGE | IN_UPDATE;
	return (error);
}

/*
 * Rewrite an existing directory entry to point at the inode
 * supplied.  The parameters describing the directory entry are
 * set up by a call to namei.
 */
int
ufs_dirrewrite(struct inode *dp, struct inode *oip, ufsino_t newinum,
    int newtype, int isrmdir)
{
	struct buf *bp;
	struct direct *ep;
	struct vnode *vdp = ITOV(dp);
	int error;

	error = UFS_BUFATOFF(dp, (off_t)dp->i_offset, (char **)&ep, &bp);
	if (error)
		return (error);
	ep->d_ino = newinum;
	ep->d_type = newtype;
	oip->i_effnlink--;
	DIP_ADD(oip, nlink, -1);
	oip->i_flag |= IN_CHANGE;
	if (DOINGASYNC(vdp)) {
		bdwrite(bp);
		error = 0;
	} else {
		error = VOP_BWRITE(bp);
	}
	dp->i_flag |= IN_CHANGE | IN_UPDATE;
	return (error);
}

/*
 * Check if a directory is empty or not.
 * Inode supplied must be locked.
 *
 * Using a struct dirtemplate here is not precisely
 * what we want, but better than using a struct direct.
 *
 * NB: does not handle corrupted directories.
 */
int
ufs_dirempty(struct inode *ip, ufsino_t parentino, struct ucred *cred)
{
	off_t off, m;
	struct dirtemplate dbuf;
	struct direct *dp = (struct direct *)&dbuf;
	int error, namlen;
	size_t count;
#define	MINDIRSIZ (sizeof (struct dirtemplate) / 2)

	m = DIP(ip, size);
	for (off = 0; off < m; off += dp->d_reclen) {
		error = vn_rdwr(UIO_READ, ITOV(ip), (caddr_t)dp, MINDIRSIZ, off,
		   UIO_SYSSPACE, IO_NODELOCKED, cred, &count, curproc);
		/*
		 * Since we read MINDIRSIZ, residual must
		 * be 0 unless we're at end of file.
		 */
		if (error || count != 0)
			return (0);
		/* avoid infinite loops */
		if (dp->d_reclen == 0)
			return (0);
		/* skip empty entries */
		if (dp->d_ino == 0)
			continue;
		/* accept only "." and ".." */
		namlen = dp->d_namlen;
		if (namlen > 2)
			return (0);
		if (dp->d_name[0] != '.')
			return (0);
		/*
		 * At this point namlen must be 1 or 2.
		 * 1 implies ".", 2 implies ".." if second
		 * char is also "."
		 */
		if (namlen == 1 && dp->d_ino == ip->i_number)
			continue;
		if (dp->d_name[1] == '.' && dp->d_ino == parentino)
			continue;
		return (0);
	}
	return (1);
}

/*
 * Check if source directory is in the path of the target directory.
 * Target is supplied locked, source is unlocked.
 * The target is always vput before returning.
 */
int
ufs_checkpath(struct inode *source, struct inode *target, struct ucred *cred)
{
	struct vnode *nextvp, *vp;
	int error, rootino, namlen;
	struct dirtemplate dirbuf;

	vp = ITOV(target);
	if (target->i_number == source->i_number) {
		error = EEXIST;
		goto out;
	}
	rootino = ROOTINO;
	error = 0;
	if (target->i_number == rootino)
		goto out;

	for (;;) {
		if (vp->v_type != VDIR) {
			error = ENOTDIR;
			break;
		}
		error = vn_rdwr(UIO_READ, vp, (caddr_t)&dirbuf,
			sizeof (struct dirtemplate), (off_t)0, UIO_SYSSPACE,
			IO_NODELOCKED, cred, NULL, curproc);
		if (error != 0)
			break;
		namlen = dirbuf.dotdot_namlen;
		if (namlen != 2 ||
		    dirbuf.dotdot_name[0] != '.' ||
		    dirbuf.dotdot_name[1] != '.') {
			error = ENOTDIR;
			break;
		}
		if (dirbuf.dotdot_ino == source->i_number) {
			error = EINVAL;
			break;
		}
		if (dirbuf.dotdot_ino == rootino)
			break;
		VOP_UNLOCK(vp);
		error = VFS_VGET(vp->v_mount, dirbuf.dotdot_ino, &nextvp);
		vrele(vp);
		if (error) {
			vp = NULL;
			break;
		}
		vp = nextvp;
	}

out:
	if (error == ENOTDIR)
		printf("checkpath: .. not a directory\n");
	if (vp != NULL)
		vput(vp);
	return (error);
}