must null ni_vp on copyin error

[unix-history] / usr / src / sys / ufs / ffs / ufs_lookup.c

/*
 * Copyright (c) 1989 The Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms are permitted
 * provided that the above copyright notice and this paragraph are
 * duplicated in all such forms and that any documentation,
 * advertising materials, and other materials related to such
 * distribution and use acknowledge that the software was developed
 * by the University of California, Berkeley.  The name of the
 * University may not be used to endorse or promote products derived
 * from this software without specific prior written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 *
 *	@(#)ufs_lookup.c	7.7 (Berkeley) %G%
 */

#include "param.h"
#include "user.h"
#include "buf.h"
#include "file.h"
#include "vnode.h"
#include "../ufs/inode.h"
#include "../ufs/fs.h"

struct	vnode *cache_lookup();
struct	nchstats nchstats;
int	dirchk = 1;

/*
 * 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.
 */
ufs_lookup(vp, ndp)
	struct vnode *vp;
	register struct nameidata *ndp;
{
	register struct vnode *vdp;	/* vnode copy of dp */
	register struct inode *dp = 0;	/* the directory we are searching */
	register struct fs *fs;		/* file system that directory is in */
	struct buf *bp = 0;		/* a buffer of directory entries */
	register struct direct *ep;	/* the current directory entry */
	int entryoffsetinblock;		/* offset of ep in bp's buffer */
	enum {NONE, COMPACT, FOUND} slotstatus;
	int slotoffset = -1;		/* 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 */
	int endsearch;			/* offset to end directory search */
	int prevoff;			/* ndp->ni_offset of previous entry */
	struct inode *pdp;		/* saved dp during symlink work */
	struct inode *tdp;		/* returned by iget */
	off_t enduseful;		/* pointer past last used dir slot */
	int flag;			/* LOOKUP, CREATE, RENAME, or DELETE */
	int lockparent;			/* 1 => lockparent flag is set */
	int wantparent;			/* 1 => wantparent or lockparent flag */
	int error;

	ndp->ni_dvp = vp;
	ndp->ni_vp = NULL;
	dp = VTOI(vp);
	fs = dp->i_fs;
	lockparent = ndp->ni_nameiop & LOCKPARENT;
	flag = ndp->ni_nameiop & OPFLAG;
	wantparent = ndp->ni_nameiop & (LOCKPARENT|WANTPARENT);

	/*
	 * Check accessiblity of directory.
	 */
	if ((dp->i_mode&IFMT) != IFDIR)
		return (ENOTDIR);
	if (error = iaccess(dp, IEXEC, ndp->ni_cred))
		return (error);

	/*
	 * 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 (vdp = cache_lookup(ndp)) {
		/*
		 * Get the next vnode in the path.
		 * See comment above `IUNLOCK' code for
		 * an explaination of the locking protocol.
		 */
		pdp = dp;
		dp = VTOI(vdp);
		if (pdp == dp) {
			vdp->v_count++;
		} else if (ndp->ni_isdotdot) {
			IUNLOCK(pdp);
			igrab(dp);
		} else {
			igrab(dp);
			IUNLOCK(pdp);
		}
		ndp->ni_vp = vdp;
		return (0);
	}

	/*
	 * 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;
	if ((flag == CREATE || flag == RENAME) && *ndp->ni_next == 0) {
		slotstatus = NONE;
		slotfreespace = 0;
		slotneeded = DIRSIZ(&ndp->ni_dent);
	}

	/*
	 * 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 (flag != LOOKUP || dp->i_diroff == 0 || dp->i_diroff > dp->i_size) {
		ndp->ni_offset = 0;
		numdirpasses = 1;
	} else {
		ndp->ni_offset = dp->i_diroff;
		entryoffsetinblock = blkoff(fs, ndp->ni_offset);
		if (entryoffsetinblock != 0) {
			error = blkatoff(dp, ndp->ni_offset, (char **)0, &bp);
			if (error)
				return (error);
		}
		numdirpasses = 2;
		nchstats.ncs_2passes++;
	}
	endsearch = roundup(dp->i_size, DIRBLKSIZ);
	enduseful = 0;

searchloop:
	while (ndp->ni_offset < endsearch) {
		/*
		 * If offset is on a block boundary,
		 * read the next directory block.
		 * Release previous if it exists.
		 */
		if (blkoff(fs, ndp->ni_offset) == 0) {
			if (bp != NULL)
				brelse(bp);
			error = blkatoff(dp, ndp->ni_offset, (char **)0, &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 *)(bp->b_un.b_addr + entryoffsetinblock);
		if (ep->d_reclen == 0 ||
		    dirchk && dirbadentry(ep, entryoffsetinblock)) {
			int i;

			dirbad(dp, ndp->ni_offset, "mangled entry");
			i = DIRBLKSIZ - (entryoffsetinblock & (DIRBLKSIZ - 1));
			ndp->ni_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 = ndp->ni_offset;
					slotsize = ep->d_reclen;
				} else if (slotstatus == NONE) {
					slotfreespace += size;
					if (slotoffset == -1)
						slotoffset = ndp->ni_offset;
					if (slotfreespace >= slotneeded) {
						slotstatus = COMPACT;
						slotsize = ndp->ni_offset +
						      ep->d_reclen - slotoffset;
					}
				}
			}
		}

		/*
		 * Check for a name match.
		 */
		if (ep->d_ino) {
			if (ep->d_namlen == ndp->ni_dent.d_namlen &&
			    !bcmp(ndp->ni_ptr, ep->d_name,
				(unsigned)ep->d_namlen)) {
				/*
				 * Save directory entry's inode number and
				 * reclen in ndp->ni_dent, and release
				 * directory buffer.
				 */
				ndp->ni_dent.d_ino = ep->d_ino;
				ndp->ni_dent.d_reclen = ep->d_reclen;
				brelse(bp);
				goto found;
			}
		}
		prevoff = ndp->ni_offset;
		ndp->ni_offset += ep->d_reclen;
		entryoffsetinblock += ep->d_reclen;
		if (ep->d_ino)
			enduseful = ndp->ni_offset;
	}
/* 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--;
		ndp->ni_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 ((flag == CREATE || flag == RENAME) &&
	    *ndp->ni_next == 0 && dp->i_nlink != 0) {
		/*
		 * Access for write is interpreted as allowing
		 * creation of files in the directory.
		 */
		if (error = iaccess(dp, IWRITE, ndp->ni_cred))
			return (error);
		/*
		 * Return an indication of where the new directory
		 * entry should be put.  If we didn't find a slot,
		 * then set ndp->ni_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
		 * [ndp->ni_offset .. ndp->ni_offset + ndp->ni_count)
		 */
		if (slotstatus == NONE) {
			ndp->ni_offset = roundup(dp->i_size, DIRBLKSIZ);
			ndp->ni_count = 0;
			enduseful = ndp->ni_offset;
		} else {
			ndp->ni_offset = slotoffset;
			ndp->ni_count = slotsize;
			if (enduseful < slotoffset + slotsize)
				enduseful = slotoffset + slotsize;
		}
		ndp->ni_endoff = roundup(enduseful, DIRBLKSIZ);
		dp->i_flag |= IUPD|ICHG;
		/*
		 * 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.
		 *
		 * NB - if the directory is unlocked, then this
		 * information cannot be used.
		 */
		if (!lockparent)
			IUNLOCK(dp);
	}
	return (ENOENT);

found:
	if (numdirpasses == 2)
		nchstats.ncs_pass2++;
	/*
	 * Check that directory length properly reflects presence
	 * of this entry.
	 */
	if (entryoffsetinblock + DIRSIZ(ep) > dp->i_size) {
		dirbad(dp, ndp->ni_offset, "i_size too small");
		dp->i_size = entryoffsetinblock + DIRSIZ(ep);
		dp->i_flag |= IUPD|ICHG;
	}

	/*
	 * Found component in pathname.
	 * If the final component of path name, save information
	 * in the cache as to where the entry was found.
	 */
	if (*ndp->ni_next == '\0' && flag == LOOKUP)
		dp->i_diroff = ndp->ni_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 (flag == DELETE && *ndp->ni_next == 0) {
		/*
		 * Write access to directory required to delete files.
		 */
		if (error = iaccess(dp, IWRITE, ndp->ni_cred))
			return (error);
		/*
		 * Return pointer to current entry in ndp->ni_offset,
		 * and distance past previous entry (if there
		 * is a previous entry in this block) in ndp->ni_count.
		 * Save directory inode pointer in ndp->ni_pdir for dirremove().
		 */
		if ((ndp->ni_offset&(DIRBLKSIZ-1)) == 0)
			ndp->ni_count = 0;
		else
			ndp->ni_count = ndp->ni_offset - prevoff;
		vdp = ITOV(dp);
		if (dp->i_number == ndp->ni_dent.d_ino) {
			vdp->v_count++;
		} else {
			pdp = dp;
			if (error = iget(dp, ndp->ni_dent.d_ino, &tdp))
				return (error);
			vdp = ITOV(tdp);
			/*
			 * If directory is "sticky", then user must own
			 * the directory, or the file in it, else he
			 * may not delete it (unless he's root). This
			 * implements append-only directories.
			 */
			if ((pdp->i_mode & ISVTX) &&
			    ndp->ni_cred->cr_uid != 0 &&
			    ndp->ni_cred->cr_uid != pdp->i_uid &&
			    tdp->i_uid != ndp->ni_cred->cr_uid) {
				iput(tdp);
				return (EPERM);
			}
		}
		ndp->ni_vp = vdp;
		if (!lockparent)
			IUNLOCK(pdp);
		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 (flag == RENAME && wantparent && *ndp->ni_next == 0) {
		if (error = iaccess(dp, IWRITE, ndp->ni_cred))
			return (error);
		/*
		 * Careful about locking second inode.
		 * This can only occur if the target is ".".
		 */
		if (dp->i_number == ndp->ni_dent.d_ino)
			return (EISDIR);
		if (error = iget(dp, ndp->ni_dent.d_ino, &tdp))
			return (error);
		ndp->ni_vp = ITOV(tdp);
		if (!lockparent)
			IUNLOCK(dp);
		return (0);
	}

	/*
	 * 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 = dp;
	if (ndp->ni_isdotdot) {
		IUNLOCK(pdp);	/* race to get the inode */
		if (error = iget(dp, ndp->ni_dent.d_ino, &tdp)) {
			ILOCK(pdp);
			return (error);
		}
		ndp->ni_vp = ITOV(tdp);
	} else if (dp->i_number == ndp->ni_dent.d_ino) {
		vdp = ITOV(dp);
		vdp->v_count++;	/* we want ourself, ie "." */
		ndp->ni_vp = vdp;
	} else {
		if (error = iget(dp, ndp->ni_dent.d_ino, &tdp))
			return (error);
		IUNLOCK(pdp);
		ndp->ni_vp = ITOV(tdp);
	}

	/*
	 * Insert name into cache if appropriate.
	 */
	if (ndp->ni_makeentry)
		cache_enter(ndp);
	return (0);
}


dirbad(ip, offset, how)
	struct inode *ip;
	off_t offset;
	char *how;
{

	printf("%s: bad dir ino %d at offset %d: %s\n",
	    ip->i_fs->fs_fsmnt, ip->i_number, offset, how);
}

/*
 * 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
 */
dirbadentry(ep, entryoffsetinblock)
	register struct direct *ep;
	int entryoffsetinblock;
{
	register int i;

	if ((ep->d_reclen & 0x3) != 0 ||
	    ep->d_reclen > DIRBLKSIZ - (entryoffsetinblock & (DIRBLKSIZ - 1)) ||
	    ep->d_reclen < DIRSIZ(ep) || ep->d_namlen > MAXNAMLEN)
		return (1);
	for (i = 0; i < ep->d_namlen; i++)
		if (ep->d_name[i] == '\0')
			return (1);
	return (ep->d_name[i]);
}

/*
 * Write a directory entry after a call to namei, using the parameters
 * which it left in nameidata.  The argument ip is the inode which the
 * new directory entry will refer to.  The nameidata field ndp->ni_dvp
 * is a pointer to the directory to be written, which was left locked by
 * namei.  Remaining parameters (ndp->ni_offset, ndp->ni_count) indicate
 * how the space for the new entry is to be gotten.
 */
direnter(ip, ndp)
	struct inode *ip;
	register struct nameidata *ndp;
{
	register struct direct *ep, *nep;
	register struct inode *dp = VTOI(ndp->ni_dvp);
	struct buf *bp;
	int loc, spacefree, error = 0;
	u_int dsize;
	int newentrysize;
	char *dirbuf;

	ndp->ni_dent.d_ino = ip->i_number;
	newentrysize = DIRSIZ(&ndp->ni_dent);
	if (ndp->ni_count == 0) {
		/*
		 * If ndp->ni_count is 0, then namei could find no space in the
		 * directory. In this case ndp->ni_offset will be on a directory
		 * block boundary and we will write the new entry into a fresh
		 * block.
		 */
		if (ndp->ni_offset&(DIRBLKSIZ-1))
			panic("wdir: newblk");
		ndp->ni_dent.d_reclen = DIRBLKSIZ;
		error = rdwri(UIO_WRITE, dp, (caddr_t)&ndp->ni_dent,
		    newentrysize, ndp->ni_offset, UIO_SYSSPACE, ndp->ni_cred,
		    (int *)0);
		if (DIRBLKSIZ > dp->i_fs->fs_fsize)
			panic("wdir: blksize"); /* XXX - should grow w/balloc */
		else
			dp->i_size = roundup(dp->i_size, DIRBLKSIZ);
		iput(dp);
		return (error);
	}

	/*
	 * If ndp->ni_count is non-zero, then namei found space for the new
	 * entry in the range ndp->ni_offset to ndp->ni_offset + ndp->ni_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 (ndp->ni_offset + ndp->ni_count > dp->i_size)
		dp->i_size = ndp->ni_offset + ndp->ni_count;
	/*
	 * Get the block containing the space for the new directory entry.
	 */
	if (error = blkatoff(dp, ndp->ni_offset, (char **)&dirbuf, &bp)) {
		iput(dp);
		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
	 * ndp->ni_offset to ndp->ni_offset+ndp->ni_count would yield the space.
	 */
	ep = (struct direct *)dirbuf;
	dsize = DIRSIZ(ep);
	spacefree = ep->d_reclen - dsize;
	for (loc = ep->d_reclen; loc < ndp->ni_count; ) {
		nep = (struct direct *)(dirbuf + loc);
		if (ep->d_ino) {
			/* trim the existing slot */
			ep->d_reclen = dsize;
			ep = (struct direct *)((char *)ep + dsize);
		} else {
			/* overwrite; nothing there; header is ours */
			spacefree += dsize;
		}
		dsize = DIRSIZ(nep);
		spacefree += nep->d_reclen - dsize;
		loc += nep->d_reclen;
		bcopy((caddr_t)nep, (caddr_t)ep, dsize);
	}
	/*
	 * 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("wdir: compact1");
		ndp->ni_dent.d_reclen = spacefree + dsize;
	} else {
		if (spacefree < newentrysize)
			panic("wdir: compact2");
		ndp->ni_dent.d_reclen = spacefree;
		ep->d_reclen = dsize;
		ep = (struct direct *)((char *)ep + dsize);
	}
	bcopy((caddr_t)&ndp->ni_dent, (caddr_t)ep, (u_int)newentrysize);
	error = bwrite(bp);
	dp->i_flag |= IUPD|ICHG;
	if (ndp->ni_endoff && ndp->ni_endoff < dp->i_size)
		error = itrunc(dp, (u_long)ndp->ni_endoff);
	iput(dp);
	return (error);
}

/*
 * Remove a directory entry after a call to namei, using the
 * parameters which it left in the u. area.  The u. entry
 * ni_offset contains the offset into the directory of the
 * entry to be eliminated.  The ni_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 isn't 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.
 */
dirremove(ndp)
	register struct nameidata *ndp;
{
	register struct inode *dp = VTOI(ndp->ni_dvp);
	struct direct *ep;
	struct buf *bp;
	int error;

	if (ndp->ni_count == 0) {
		/*
		 * First entry in block: set d_ino to zero.
		 */
		ndp->ni_dent.d_ino = 0;
		error = rdwri(UIO_WRITE, dp, (caddr_t)&ndp->ni_dent,
		    (int)DIRSIZ(&ndp->ni_dent), ndp->ni_offset, UIO_SYSSPACE,
		    ndp->ni_cred, (int *)0);
	} else {
		/*
		 * Collapse new free space into previous entry.
		 */
		if (error = blkatoff(dp, ndp->ni_offset - ndp->ni_count,
		    (char **)&ep, &bp)) {
			return (error);
		}
		ep->d_reclen += ndp->ni_dent.d_reclen;
		error = bwrite(bp);
		dp->i_flag |= IUPD|ICHG;
	}
	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.
 */
dirrewrite(dp, ip, ndp)
	struct inode *dp, *ip;
	struct nameidata *ndp;
{

	ndp->ni_dent.d_ino = ip->i_number;
	return (rdwri(UIO_WRITE, dp, (caddr_t)&ndp->ni_dent,
	    (int)DIRSIZ(&ndp->ni_dent), ndp->ni_offset, UIO_SYSSPACE,
	    ndp->ni_cred, (int *)0));
}

/*
 * Return buffer with contents of block "offset"
 * from the beginning of directory "ip".  If "res"
 * is non-zero, fill it in with a pointer to the
 * remaining space in the directory.
 */
blkatoff(ip, offset, res, bpp)
	struct inode *ip;
	off_t offset;
	char **res;
	struct buf **bpp;
{
	register struct fs *fs = ip->i_fs;
	daddr_t lbn = lblkno(fs, offset);
	int bsize = blksize(fs, ip, lbn);
	struct buf *bp;
	daddr_t bn;
	int error;

	*bpp = 0;
	if (error = bmap(ip, lbn, &bn, (daddr_t *)0, (int *)0))
		return (error);
	if (bn == (daddr_t)-1) {
		dirbad(ip, offset, "hole in dir");
		return (EIO);
	}
#ifdef SECSIZE
	bp = bread(ip->i_dev, fsbtodb(fs, bn), bsize, fs->fs_dbsize);
#else SECSIZE
	error = bread(ip->i_devvp, bn, bsize, &bp);
	if (error) {
		brelse(bp);
		return (error);
	}
	if (res)
		*res = bp->b_un.b_addr + blkoff(fs, offset);
	*bpp = bp;
	return (0);
}

/*
 * 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.
 */
dirempty(ip, parentino, cred)
	register struct inode *ip;
	ino_t parentino;
	struct ucred *cred;
{
	register off_t off;
	struct dirtemplate dbuf;
	register struct direct *dp = (struct direct *)&dbuf;
	int error, count;
#define	MINDIRSIZ (sizeof (struct dirtemplate) / 2)

	for (off = 0; off < ip->i_size; off += dp->d_reclen) {
		error = rdwri(UIO_READ, ip, (caddr_t)dp, MINDIRSIZ, off,
		    UIO_SYSSPACE, cred, &count);
		/*
		 * 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 ".." */
		if (dp->d_namlen > 2)
			return (0);
		if (dp->d_name[0] != '.')
			return (0);
		/*
		 * At this point d_namlen must be 1 or 2.
		 * 1 implies ".", 2 implies ".." if second
		 * char is also "."
		 */
		if (dp->d_namlen == 1)
			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 iput() before returning.
 */
checkpath(source, target, cred)
	struct inode *source, *target;
	struct ucred *cred;
{
	struct dirtemplate dirbuf;
	struct inode *ip;
	int error = 0;

	ip = target;
	if (ip->i_number == source->i_number) {
		error = EEXIST;
		goto out;
	}
	if (ip->i_number == ROOTINO)
		goto out;

	for (;;) {
		if ((ip->i_mode&IFMT) != IFDIR) {
			error = ENOTDIR;
			break;
		}
		error = rdwri(UIO_READ, ip, (caddr_t)&dirbuf,
			sizeof (struct dirtemplate), (off_t)0, UIO_SYSSPACE,
			cred, (int *)0);
		if (error != 0)
			break;
		if (dirbuf.dotdot_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;
		iput(ip);
		if (error = iget(ip, dirbuf.dotdot_ino, &ip))
			break;
	}

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