freebsd-skq/sys/fs/tmpfs/tmpfs_subr.c

/*	$NetBSD: tmpfs_subr.c,v 1.21 2006/06/07 22:33:39 kardel Exp $	*/

/*
 * Copyright (c) 2005 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Julio M. Merino Vidal, developed as part of Google's Summer of Code
 * 2005 program.
 *
 * 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 NetBSD
 *        Foundation, Inc. and its contributors.
 * 4. Neither the name of The NetBSD Foundation 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 NETBSD FOUNDATION, INC. 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 FOUNDATION 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.
 */

/*
 * Efficient memory file system supporting functions.
 */
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include <sys/param.h>
#include <sys/namei.h>
#include <sys/priv.h>
#include <sys/proc.h>
#include <sys/stat.h>
#include <sys/systm.h>
#include <sys/vnode.h>
#include <sys/vmmeter.h>

#include <vm/vm.h>
#include <vm/vm_object.h>
#include <vm/vm_page.h>
#include <vm/vm_pager.h>
#include <vm/vm_extern.h>

#include <fs/tmpfs/tmpfs.h>
#include <fs/tmpfs/tmpfs_fifoops.h>
#include <fs/tmpfs/tmpfs_vnops.h>

/* --------------------------------------------------------------------- */

/*
 * Allocates a new node of type 'type' inside the 'tmp' mount point, with
 * its owner set to 'uid', its group to 'gid' and its mode set to 'mode',
 * using the credentials of the process 'p'.
 *
 * If the node type is set to 'VDIR', then the parent parameter must point
 * to the parent directory of the node being created.  It may only be NULL
 * while allocating the root node.
 *
 * If the node type is set to 'VBLK' or 'VCHR', then the rdev parameter
 * specifies the device the node represents.
 *
 * If the node type is set to 'VLNK', then the parameter target specifies
 * the file name of the target file for the symbolic link that is being
 * created.
 *
 * Note that new nodes are retrieved from the available list if it has
 * items or, if it is empty, from the node pool as long as there is enough
 * space to create them.
 *
 * Returns zero on success or an appropriate error code on failure.
 */
int
tmpfs_alloc_node(struct tmpfs_mount *tmp, enum vtype type,
    uid_t uid, gid_t gid, mode_t mode, struct tmpfs_node *parent,
    char *target, dev_t rdev, struct thread *p, struct tmpfs_node **node)
{
	struct tmpfs_node *nnode;

	/* If the root directory of the 'tmp' file system is not yet
	 * allocated, this must be the request to do it. */
	MPASS(IMPLIES(tmp->tm_root == NULL, parent == NULL && type == VDIR));

	MPASS(IFF(type == VLNK, target != NULL));
	MPASS(IFF(type == VBLK || type == VCHR, rdev != VNOVAL));

	if (tmp->tm_nodes_inuse > tmp->tm_nodes_max)
		return (ENOSPC);

	nnode = (struct tmpfs_node *)uma_zalloc_arg(
				tmp->tm_node_pool, tmp, M_WAITOK);

	/* Generic initialization. */
	nnode->tn_type = type;
	vfs_timestamp(&nnode->tn_atime);
	nnode->tn_birthtime = nnode->tn_ctime = nnode->tn_mtime =
	    nnode->tn_atime;
	nnode->tn_uid = uid;
	nnode->tn_gid = gid;
	nnode->tn_mode = mode;
	nnode->tn_id = alloc_unr(tmp->tm_ino_unr);

	/* Type-specific initialization. */
	switch (nnode->tn_type) {
	case VBLK:
	case VCHR:
		nnode->tn_rdev = rdev;
		break;

	case VDIR:
		TAILQ_INIT(&nnode->tn_dir.tn_dirhead);
		nnode->tn_dir.tn_parent = (parent == NULL) ? nnode : parent;
		nnode->tn_dir.tn_readdir_lastn = 0;
		nnode->tn_dir.tn_readdir_lastp = NULL;
		nnode->tn_links++;
		nnode->tn_dir.tn_parent->tn_links++;
		break;

	case VFIFO:
		/* FALLTHROUGH */
	case VSOCK:
		break;

	case VLNK:
		MPASS(strlen(target) < MAXPATHLEN);
		nnode->tn_size = strlen(target);
		nnode->tn_link = malloc(nnode->tn_size, M_TMPFSNAME,
		    M_WAITOK);
		memcpy(nnode->tn_link, target, nnode->tn_size);
		break;

	case VREG:
		nnode->tn_reg.tn_aobj =
		    vm_pager_allocate(OBJT_SWAP, NULL, 0, VM_PROT_DEFAULT, 0);
		nnode->tn_reg.tn_aobj_pages = 0;
		break;

	default:
		MPASS(0);
	}

	TMPFS_LOCK(tmp);
	LIST_INSERT_HEAD(&tmp->tm_nodes_used, nnode, tn_entries);
	tmp->tm_nodes_inuse++;
	TMPFS_UNLOCK(tmp);

	*node = nnode;
	return 0;
}

/* --------------------------------------------------------------------- */

/*
 * Destroys the node pointed to by node from the file system 'tmp'.
 * If the node does not belong to the given mount point, the results are
 * unpredicted.
 *
 * If the node references a directory; no entries are allowed because
 * their removal could need a recursive algorithm, something forbidden in
 * kernel space.  Furthermore, there is not need to provide such
 * functionality (recursive removal) because the only primitives offered
 * to the user are the removal of empty directories and the deletion of
 * individual files.
 *
 * Note that nodes are not really deleted; in fact, when a node has been
 * allocated, it cannot be deleted during the whole life of the file
 * system.  Instead, they are moved to the available list and remain there
 * until reused.
 */
void
tmpfs_free_node(struct tmpfs_mount *tmp, struct tmpfs_node *node)
{
	size_t pages = 0;

#ifdef INVARIANTS
	TMPFS_NODE_LOCK(node);
	MPASS(node->tn_vnode == NULL);
	TMPFS_NODE_UNLOCK(node);
#endif

	TMPFS_LOCK(tmp);
	LIST_REMOVE(node, tn_entries);
	tmp->tm_nodes_inuse--;
	TMPFS_UNLOCK(tmp);

	switch (node->tn_type) {
	case VNON:
		/* Do not do anything.  VNON is provided to let the
		 * allocation routine clean itself easily by avoiding
		 * duplicating code in it. */
		/* FALLTHROUGH */
	case VBLK:
		/* FALLTHROUGH */
	case VCHR:
		/* FALLTHROUGH */
	case VDIR:
		/* FALLTHROUGH */
	case VFIFO:
		/* FALLTHROUGH */
	case VSOCK:
		break;

	case VLNK:
		free(node->tn_link, M_TMPFSNAME);
		break;

	case VREG:
		if (node->tn_reg.tn_aobj != NULL)
			vm_object_deallocate(node->tn_reg.tn_aobj);
		pages = node->tn_reg.tn_aobj_pages;
		break;

	default:
		MPASS(0);
		break;
	}

	free_unr(tmp->tm_ino_unr, node->tn_id);
	uma_zfree(tmp->tm_node_pool, node);

	TMPFS_LOCK(tmp);
	tmp->tm_pages_used -= pages;
	TMPFS_UNLOCK(tmp);
}

/* --------------------------------------------------------------------- */

/*
 * Allocates a new directory entry for the node node with a name of name.
 * The new directory entry is returned in *de.
 *
 * The link count of node is increased by one to reflect the new object
 * referencing it.
 *
 * Returns zero on success or an appropriate error code on failure.
 */
int
tmpfs_alloc_dirent(struct tmpfs_mount *tmp, struct tmpfs_node *node,
    const char *name, uint16_t len, struct tmpfs_dirent **de)
{
	struct tmpfs_dirent *nde;

	nde = (struct tmpfs_dirent *)uma_zalloc(
					tmp->tm_dirent_pool, M_WAITOK);
	nde->td_name = malloc(len, M_TMPFSNAME, M_WAITOK);
	nde->td_namelen = len;
	memcpy(nde->td_name, name, len);

	nde->td_node = node;
	node->tn_links++;

	*de = nde;

	return 0;
}

/* --------------------------------------------------------------------- */

/*
 * Frees a directory entry.  It is the caller's responsibility to destroy
 * the node referenced by it if needed.
 *
 * The link count of node is decreased by one to reflect the removal of an
 * object that referenced it.  This only happens if 'node_exists' is true;
 * otherwise the function will not access the node referred to by the
 * directory entry, as it may already have been released from the outside.
 */
void
tmpfs_free_dirent(struct tmpfs_mount *tmp, struct tmpfs_dirent *de,
    boolean_t node_exists)
{
	if (node_exists) {
		struct tmpfs_node *node;

		node = de->td_node;

		MPASS(node->tn_links > 0);
		node->tn_links--;
	}

	free(de->td_name, M_TMPFSNAME);
	uma_zfree(tmp->tm_dirent_pool, de);
}

/* --------------------------------------------------------------------- */

/*
 * Allocates a new vnode for the node node or returns a new reference to
 * an existing one if the node had already a vnode referencing it.  The
 * resulting locked vnode is returned in *vpp.
 *
 * Returns zero on success or an appropriate error code on failure.
 */
int
tmpfs_alloc_vp(struct mount *mp, struct tmpfs_node *node, int lkflag,
    struct vnode **vpp, struct thread *td)
{
	int error;
	struct vnode *vp;

loop:
	TMPFS_NODE_LOCK(node);
	if ((vp = node->tn_vnode) != NULL) {
		VI_LOCK(vp);
		TMPFS_NODE_UNLOCK(node);
		vholdl(vp);
		error = vget(vp, lkflag | LK_INTERLOCK | LK_RETRY, td);
		vdrop(vp);
		if (error)
			return error;

		/*
		 * Make sure the vnode is still there after
		 * getting the interlock to avoid racing a free.
		 */
		if (node->tn_vnode == NULL || node->tn_vnode != vp) {
			vput(vp);
			goto loop;
		}

		goto out;
	}

	/*
	 * otherwise lock the vp list while we call getnewvnode
	 * since that can block.
	 */
	if (node->tn_vpstate & TMPFS_VNODE_ALLOCATING) {
		node->tn_vpstate |= TMPFS_VNODE_WANT;
		error = msleep((caddr_t) &node->tn_vpstate,
		    TMPFS_NODE_MTX(node), PDROP | PCATCH,
		    "tmpfs_alloc_vp", 0);
		if (error)
			return error;

		goto loop;
	} else
		node->tn_vpstate |= TMPFS_VNODE_ALLOCATING;
	
	TMPFS_NODE_UNLOCK(node);

	/* Get a new vnode and associate it with our node. */
	error = getnewvnode("tmpfs", mp, &tmpfs_vnodeop_entries, &vp);
	if (error != 0)
		goto unlock;
	MPASS(vp != NULL);

	error = vn_lock(vp, lkflag | LK_RETRY, td);
	if (error != 0) {
		vp->v_data = NULL;
		vput(vp);
		vp = NULL;
		goto unlock;
	}

	vp->v_data = node;
	vp->v_type = node->tn_type;

	/* Type-specific initialization. */
	switch (node->tn_type) {
	case VBLK:
		/* FALLTHROUGH */
	case VCHR:
		/* FALLTHROUGH */
	case VDIR:
		/* FALLTHROUGH */
	case VLNK:
		/* FALLTHROUGH */
	case VREG:
		/* FALLTHROUGH */
	case VSOCK:
		break;
	case VFIFO:
		vp->v_op = &tmpfs_fifoop_entries;
		break;

	default:
		MPASS(0);
	}

	vnode_pager_setsize(vp, node->tn_size);
	error = insmntque(vp, mp);
	if (error)
		vp = NULL;

unlock:
	TMPFS_NODE_LOCK(node);

	MPASS(node->tn_vpstate & TMPFS_VNODE_ALLOCATING);
	node->tn_vpstate &= ~TMPFS_VNODE_ALLOCATING;
	node->tn_vnode = vp;

	if (node->tn_vpstate & TMPFS_VNODE_WANT) {
		node->tn_vpstate &= ~TMPFS_VNODE_WANT;
		TMPFS_NODE_UNLOCK(node);
		wakeup((caddr_t) &node->tn_vpstate);
	} else
		TMPFS_NODE_UNLOCK(node);

out:
	*vpp = vp;

	MPASS(IFF(error == 0, *vpp != NULL && VOP_ISLOCKED(*vpp, td)));
#ifdef INVARIANTS
	TMPFS_NODE_LOCK(node);
	MPASS(*vpp == node->tn_vnode);
	TMPFS_NODE_UNLOCK(node);
#endif

	return error;
}

/* --------------------------------------------------------------------- */

/*
 * Destroys the association between the vnode vp and the node it
 * references.
 */
void
tmpfs_free_vp(struct vnode *vp)
{
	struct tmpfs_node *node;

	node = VP_TO_TMPFS_NODE(vp);

	TMPFS_NODE_LOCK(node);
	node->tn_vnode = NULL;
	vp->v_data = NULL;
	TMPFS_NODE_UNLOCK(node);
}

/* --------------------------------------------------------------------- */

/*
 * Allocates a new file of type 'type' and adds it to the parent directory
 * 'dvp'; this addition is done using the component name given in 'cnp'.
 * The ownership of the new file is automatically assigned based on the
 * credentials of the caller (through 'cnp'), the group is set based on
 * the parent directory and the mode is determined from the 'vap' argument.
 * If successful, *vpp holds a vnode to the newly created file and zero
 * is returned.  Otherwise *vpp is NULL and the function returns an
 * appropriate error code.
 */
int
tmpfs_alloc_file(struct vnode *dvp, struct vnode **vpp, struct vattr *vap,
    struct componentname *cnp, char *target)
{
	int error;
	struct tmpfs_dirent *de;
	struct tmpfs_mount *tmp;
	struct tmpfs_node *dnode;
	struct tmpfs_node *node;
	struct tmpfs_node *parent;

	MPASS(VOP_ISLOCKED(dvp, cnp->cn_thread));
	MPASS(cnp->cn_flags & HASBUF);

	tmp = VFS_TO_TMPFS(dvp->v_mount);
	dnode = VP_TO_TMPFS_DIR(dvp);
	*vpp = NULL;

	/* If the entry we are creating is a directory, we cannot overflow
	 * the number of links of its parent, because it will get a new
	 * link. */
	if (vap->va_type == VDIR) {
		/* Ensure that we do not overflow the maximum number of links
		 * imposed by the system. */
		MPASS(dnode->tn_links <= LINK_MAX);
		if (dnode->tn_links == LINK_MAX) {
			error = EMLINK;
			goto out;
		}

		parent = dnode;
	} else
		parent = NULL;

	/* Allocate a node that represents the new file. */
	error = tmpfs_alloc_node(tmp, vap->va_type, cnp->cn_cred->cr_uid,
	    dnode->tn_gid, vap->va_mode, parent, target, vap->va_rdev,
	    cnp->cn_thread, &node);
	if (error != 0)
		goto out;

	/* Allocate a directory entry that points to the new file. */
	error = tmpfs_alloc_dirent(tmp, node, cnp->cn_nameptr, cnp->cn_namelen,
	    &de);
	if (error != 0) {
		tmpfs_free_node(tmp, node);
		goto out;
	}

	/* Allocate a vnode for the new file. */
	error = tmpfs_alloc_vp(dvp->v_mount, node, LK_EXCLUSIVE, vpp,
	    cnp->cn_thread);
	if (error != 0) {
		tmpfs_free_dirent(tmp, de, TRUE);
		tmpfs_free_node(tmp, node);
		goto out;
	}

	/* Now that all required items are allocated, we can proceed to
	 * insert the new node into the directory, an operation that
	 * cannot fail. */
	tmpfs_dir_attach(dvp, de);

out:

	return error;
}

/* --------------------------------------------------------------------- */

/*
 * Attaches the directory entry de to the directory represented by vp.
 * Note that this does not change the link count of the node pointed by
 * the directory entry, as this is done by tmpfs_alloc_dirent.
 */
void
tmpfs_dir_attach(struct vnode *vp, struct tmpfs_dirent *de)
{
	struct tmpfs_node *dnode;

	ASSERT_VOP_ELOCKED(vp, __func__);
	dnode = VP_TO_TMPFS_DIR(vp);
	TAILQ_INSERT_TAIL(&dnode->tn_dir.tn_dirhead, de, td_entries);
	dnode->tn_size += sizeof(struct tmpfs_dirent);
	dnode->tn_status |= TMPFS_NODE_ACCESSED | TMPFS_NODE_CHANGED | \
	    TMPFS_NODE_MODIFIED;
}

/* --------------------------------------------------------------------- */

/*
 * Detaches the directory entry de from the directory represented by vp.
 * Note that this does not change the link count of the node pointed by
 * the directory entry, as this is done by tmpfs_free_dirent.
 */
void
tmpfs_dir_detach(struct vnode *vp, struct tmpfs_dirent *de)
{
	struct tmpfs_node *dnode;

	ASSERT_VOP_ELOCKED(vp, __func__);
	dnode = VP_TO_TMPFS_DIR(vp);

	if (dnode->tn_dir.tn_readdir_lastp == de) {
		dnode->tn_dir.tn_readdir_lastn = 0;
		dnode->tn_dir.tn_readdir_lastp = NULL;
	}

	TAILQ_REMOVE(&dnode->tn_dir.tn_dirhead, de, td_entries);
	dnode->tn_size -= sizeof(struct tmpfs_dirent);
	dnode->tn_status |= TMPFS_NODE_ACCESSED | TMPFS_NODE_CHANGED | \
	    TMPFS_NODE_MODIFIED;
}

/* --------------------------------------------------------------------- */

/*
 * Looks for a directory entry in the directory represented by node.
 * 'cnp' describes the name of the entry to look for.  Note that the .
 * and .. components are not allowed as they do not physically exist
 * within directories.
 *
 * Returns a pointer to the entry when found, otherwise NULL.
 */
struct tmpfs_dirent *
tmpfs_dir_lookup(struct tmpfs_node *node, struct componentname *cnp)
{
	boolean_t found;
	struct tmpfs_dirent *de;

	MPASS(IMPLIES(cnp->cn_namelen == 1, cnp->cn_nameptr[0] != '.'));
	MPASS(IMPLIES(cnp->cn_namelen == 2, !(cnp->cn_nameptr[0] == '.' &&
	    cnp->cn_nameptr[1] == '.')));
	TMPFS_VALIDATE_DIR(node);

	found = 0;
	TAILQ_FOREACH(de, &node->tn_dir.tn_dirhead, td_entries) {
		MPASS(cnp->cn_namelen < 0xffff);
		if (de->td_namelen == (uint16_t)cnp->cn_namelen &&
		    memcmp(de->td_name, cnp->cn_nameptr, de->td_namelen) == 0) {
			found = 1;
			break;
		}
	}
	node->tn_status |= TMPFS_NODE_ACCESSED;

	return found ? de : NULL;
}

/* --------------------------------------------------------------------- */

/*
 * Helper function for tmpfs_readdir.  Creates a '.' entry for the given
 * directory and returns it in the uio space.  The function returns 0
 * on success, -1 if there was not enough space in the uio structure to
 * hold the directory entry or an appropriate error code if another
 * error happens.
 */
int
tmpfs_dir_getdotdent(struct tmpfs_node *node, struct uio *uio)
{
	int error;
	struct dirent dent;

	TMPFS_VALIDATE_DIR(node);
	MPASS(uio->uio_offset == TMPFS_DIRCOOKIE_DOT);

	dent.d_fileno = node->tn_id;
	dent.d_type = DT_DIR;
	dent.d_namlen = 1;
	dent.d_name[0] = '.';
	dent.d_name[1] = '\0';
	dent.d_reclen = GENERIC_DIRSIZ(&dent);

	if (dent.d_reclen > uio->uio_resid)
		error = -1;
	else {
		error = uiomove(&dent, dent.d_reclen, uio);
		if (error == 0)
			uio->uio_offset = TMPFS_DIRCOOKIE_DOTDOT;
	}

	node->tn_status |= TMPFS_NODE_ACCESSED;

	return error;
}

/* --------------------------------------------------------------------- */

/*
 * Helper function for tmpfs_readdir.  Creates a '..' entry for the given
 * directory and returns it in the uio space.  The function returns 0
 * on success, -1 if there was not enough space in the uio structure to
 * hold the directory entry or an appropriate error code if another
 * error happens.
 */
int
tmpfs_dir_getdotdotdent(struct tmpfs_node *node, struct uio *uio)
{
	int error;
	struct dirent dent;

	TMPFS_VALIDATE_DIR(node);
	MPASS(uio->uio_offset == TMPFS_DIRCOOKIE_DOTDOT);

	dent.d_fileno = node->tn_dir.tn_parent->tn_id;
	dent.d_type = DT_DIR;
	dent.d_namlen = 2;
	dent.d_name[0] = '.';
	dent.d_name[1] = '.';
	dent.d_name[2] = '\0';
	dent.d_reclen = GENERIC_DIRSIZ(&dent);

	if (dent.d_reclen > uio->uio_resid)
		error = -1;
	else {
		error = uiomove(&dent, dent.d_reclen, uio);
		if (error == 0) {
			struct tmpfs_dirent *de;

			de = TAILQ_FIRST(&node->tn_dir.tn_dirhead);
			if (de == NULL)
				uio->uio_offset = TMPFS_DIRCOOKIE_EOF;
			else
				uio->uio_offset = TMPFS_DIRCOOKIE(de);
		}
	}

	node->tn_status |= TMPFS_NODE_ACCESSED;

	return error;
}

/* --------------------------------------------------------------------- */

/*
 * Lookup a directory entry by its associated cookie.
 */
struct tmpfs_dirent *
tmpfs_dir_lookupbycookie(struct tmpfs_node *node, off_t cookie)
{
	struct tmpfs_dirent *de;

	if (cookie == node->tn_dir.tn_readdir_lastn &&
	    node->tn_dir.tn_readdir_lastp != NULL) {
		return node->tn_dir.tn_readdir_lastp;
	}

	TAILQ_FOREACH(de, &node->tn_dir.tn_dirhead, td_entries) {
		if (TMPFS_DIRCOOKIE(de) == cookie) {
			break;
		}
	}

	return de;
}

/* --------------------------------------------------------------------- */

/*
 * Helper function for tmpfs_readdir.  Returns as much directory entries
 * as can fit in the uio space.  The read starts at uio->uio_offset.
 * The function returns 0 on success, -1 if there was not enough space
 * in the uio structure to hold the directory entry or an appropriate
 * error code if another error happens.
 */
int
tmpfs_dir_getdents(struct tmpfs_node *node, struct uio *uio, off_t *cntp)
{
	int error;
	off_t startcookie;
	struct tmpfs_dirent *de;

	TMPFS_VALIDATE_DIR(node);

	/* Locate the first directory entry we have to return.  We have cached
	 * the last readdir in the node, so use those values if appropriate.
	 * Otherwise do a linear scan to find the requested entry. */
	startcookie = uio->uio_offset;
	MPASS(startcookie != TMPFS_DIRCOOKIE_DOT);
	MPASS(startcookie != TMPFS_DIRCOOKIE_DOTDOT);
	if (startcookie == TMPFS_DIRCOOKIE_EOF) {
		return 0;
	} else {
		de = tmpfs_dir_lookupbycookie(node, startcookie);
	}
	if (de == NULL) {
		return EINVAL;
	}

	/* Read as much entries as possible; i.e., until we reach the end of
	 * the directory or we exhaust uio space. */
	do {
		struct dirent d;

		/* Create a dirent structure representing the current
		 * tmpfs_node and fill it. */
		d.d_fileno = de->td_node->tn_id;
		switch (de->td_node->tn_type) {
		case VBLK:
			d.d_type = DT_BLK;
			break;

		case VCHR:
			d.d_type = DT_CHR;
			break;

		case VDIR:
			d.d_type = DT_DIR;
			break;

		case VFIFO:
			d.d_type = DT_FIFO;
			break;

		case VLNK:
			d.d_type = DT_LNK;
			break;

		case VREG:
			d.d_type = DT_REG;
			break;

		case VSOCK:
			d.d_type = DT_SOCK;
			break;

		default:
			MPASS(0);
		}
		d.d_namlen = de->td_namelen;
		MPASS(de->td_namelen < sizeof(d.d_name));
		(void)memcpy(d.d_name, de->td_name, de->td_namelen);
		d.d_name[de->td_namelen] = '\0';
		d.d_reclen = GENERIC_DIRSIZ(&d);

		/* Stop reading if the directory entry we are treating is
		 * bigger than the amount of data that can be returned. */
		if (d.d_reclen > uio->uio_resid) {
			error = -1;
			break;
		}

		/* Copy the new dirent structure into the output buffer and
		 * advance pointers. */
		error = uiomove(&d, d.d_reclen, uio);

		(*cntp)++;
		de = TAILQ_NEXT(de, td_entries);
	} while (error == 0 && uio->uio_resid > 0 && de != NULL);

	/* Update the offset and cache. */
	if (de == NULL) {
		uio->uio_offset = TMPFS_DIRCOOKIE_EOF;
		node->tn_dir.tn_readdir_lastn = 0;
		node->tn_dir.tn_readdir_lastp = NULL;
	} else {
		node->tn_dir.tn_readdir_lastn = uio->uio_offset = TMPFS_DIRCOOKIE(de);
		node->tn_dir.tn_readdir_lastp = de;
	}

	node->tn_status |= TMPFS_NODE_ACCESSED;
	return error;
}

/* --------------------------------------------------------------------- */

/*
 * Resizes the aobj associated to the regular file pointed to by vp to
 * the size newsize.  'vp' must point to a vnode that represents a regular
 * file.  'newsize' must be positive.
 *
 * Returns zero on success or an appropriate error code on failure.
 */
int
tmpfs_reg_resize(struct vnode *vp, off_t newsize)
{
	int error;
	size_t newpages, oldpages;
	struct tmpfs_mount *tmp;
	struct tmpfs_node *node;
	off_t oldsize;

	MPASS(vp->v_type == VREG);
	MPASS(newsize >= 0);

	node = VP_TO_TMPFS_NODE(vp);
	tmp = VFS_TO_TMPFS(vp->v_mount);

	/* Convert the old and new sizes to the number of pages needed to
	 * store them.  It may happen that we do not need to do anything
	 * because the last allocated page can accommodate the change on
	 * its own. */
	oldsize = node->tn_size;
	oldpages = round_page(oldsize) / PAGE_SIZE;
	MPASS(oldpages == node->tn_reg.tn_aobj_pages);
	newpages = round_page(newsize) / PAGE_SIZE;

	if (newpages > oldpages &&
	    newpages - oldpages > TMPFS_PAGES_AVAIL(tmp)) {
		error = ENOSPC;
		goto out;
	}

	node->tn_reg.tn_aobj_pages = newpages;

	TMPFS_LOCK(tmp);
	tmp->tm_pages_used += (newpages - oldpages);
	TMPFS_UNLOCK(tmp);

	node->tn_size = newsize;
	vnode_pager_setsize(vp, newsize);
	if (newsize < oldsize) {
		size_t zerolen = round_page(newsize) - newsize;
		vm_object_t uobj = node->tn_reg.tn_aobj;
		vm_page_t m;

		/*
		 * free "backing store"
		 */
		VM_OBJECT_LOCK(uobj);
		if (newpages < oldpages) {
			swap_pager_freespace(uobj,
						newpages, oldpages - newpages);
			vm_object_page_remove(uobj,
				OFF_TO_IDX(newsize + PAGE_MASK), 0, FALSE);
		}

		/*
		 * zero out the truncated part of the last page.
		 */

		if (zerolen > 0) {
			m = vm_page_grab(uobj, OFF_TO_IDX(newsize),
					VM_ALLOC_NORMAL | VM_ALLOC_RETRY);
			pmap_zero_page_area(m, PAGE_SIZE - zerolen,
				zerolen);
			vm_page_wakeup(m);
		}
		VM_OBJECT_UNLOCK(uobj);

	}

	error = 0;

out:
	return error;
}

/* --------------------------------------------------------------------- */

/*
 * Change flags of the given vnode.
 * Caller should execute tmpfs_update on vp after a successful execution.
 * The vnode must be locked on entry and remain locked on exit.
 */
int
tmpfs_chflags(struct vnode *vp, int flags, struct ucred *cred, struct thread *p)
{
	int error;
	struct tmpfs_node *node;

	MPASS(VOP_ISLOCKED(vp, p));

	node = VP_TO_TMPFS_NODE(vp);

	/* Disallow this operation if the file system is mounted read-only. */
	if (vp->v_mount->mnt_flag & MNT_RDONLY)
		return EROFS;

	/*
	 * Callers may only modify the file flags on objects they
	 * have VADMIN rights for.
	 */
	if ((error = VOP_ACCESS(vp, VADMIN, cred, p)))
		return (error);
	/*
	 * Unprivileged processes are not permitted to unset system
	 * flags, or modify flags if any system flags are set.
	 */
	if (!priv_check_cred(cred, PRIV_VFS_SYSFLAGS, 0)) {
		if (node->tn_flags
		  & (SF_NOUNLINK | SF_IMMUTABLE | SF_APPEND)) {
			error = securelevel_gt(cred, 0);
			if (error)
				return (error);
		}
		/* Snapshot flag cannot be set or cleared */
		if (((flags & SF_SNAPSHOT) != 0 &&
		  (node->tn_flags & SF_SNAPSHOT) == 0) ||
		  ((flags & SF_SNAPSHOT) == 0 &&
		  (node->tn_flags & SF_SNAPSHOT) != 0))
			return (EPERM);
		node->tn_flags = flags;
	} else {
		if (node->tn_flags
		  & (SF_NOUNLINK | SF_IMMUTABLE | SF_APPEND) ||
		  (flags & UF_SETTABLE) != flags)
			return (EPERM);
		node->tn_flags &= SF_SETTABLE;
		node->tn_flags |= (flags & UF_SETTABLE);
	}
	node->tn_status |= TMPFS_NODE_CHANGED;

	MPASS(VOP_ISLOCKED(vp, p));

	return 0;
}

/* --------------------------------------------------------------------- */

/*
 * Change access mode on the given vnode.
 * Caller should execute tmpfs_update on vp after a successful execution.
 * The vnode must be locked on entry and remain locked on exit.
 */
int
tmpfs_chmod(struct vnode *vp, mode_t mode, struct ucred *cred, struct thread *p)
{
	int error;
	struct tmpfs_node *node;

	MPASS(VOP_ISLOCKED(vp, p));

	node = VP_TO_TMPFS_NODE(vp);

	/* Disallow this operation if the file system is mounted read-only. */
	if (vp->v_mount->mnt_flag & MNT_RDONLY)
		return EROFS;

	/* Immutable or append-only files cannot be modified, either. */
	if (node->tn_flags & (IMMUTABLE | APPEND))
		return EPERM;

	/*
	 * To modify the permissions on a file, must possess VADMIN
	 * for that file.
	 */
	if ((error = VOP_ACCESS(vp, VADMIN, cred, p)))
		return (error);

	/*
	 * Privileged processes may set the sticky bit on non-directories,
	 * as well as set the setgid bit on a file with a group that the
	 * process is not a member of.
	 */
	if (vp->v_type != VDIR && (mode & S_ISTXT)) {
		if (priv_check_cred(cred, PRIV_VFS_STICKYFILE, 0))
			return (EFTYPE);
	}
	if (!groupmember(node->tn_gid, cred) && (mode & S_ISGID)) {
		error = priv_check_cred(cred, PRIV_VFS_SETGID, 0);
		if (error)
			return (error);
	}


	node->tn_mode &= ~ALLPERMS;
	node->tn_mode |= mode & ALLPERMS;

	node->tn_status |= TMPFS_NODE_CHANGED;

	MPASS(VOP_ISLOCKED(vp, p));

	return 0;
}

/* --------------------------------------------------------------------- */

/*
 * Change ownership of the given vnode.  At least one of uid or gid must
 * be different than VNOVAL.  If one is set to that value, the attribute
 * is unchanged.
 * Caller should execute tmpfs_update on vp after a successful execution.
 * The vnode must be locked on entry and remain locked on exit.
 */
int
tmpfs_chown(struct vnode *vp, uid_t uid, gid_t gid, struct ucred *cred,
    struct thread *p)
{
	int error;
	struct tmpfs_node *node;
	uid_t ouid;
	gid_t ogid;

	MPASS(VOP_ISLOCKED(vp, p));

	node = VP_TO_TMPFS_NODE(vp);

	/* Assign default values if they are unknown. */
	MPASS(uid != VNOVAL || gid != VNOVAL);
	if (uid == VNOVAL)
		uid = node->tn_uid;
	if (gid == VNOVAL)
		gid = node->tn_gid;
	MPASS(uid != VNOVAL && gid != VNOVAL);

	/* Disallow this operation if the file system is mounted read-only. */
	if (vp->v_mount->mnt_flag & MNT_RDONLY)
		return EROFS;

	/* Immutable or append-only files cannot be modified, either. */
	if (node->tn_flags & (IMMUTABLE | APPEND))
		return EPERM;

	/*
	 * To modify the ownership of a file, must possess VADMIN for that
	 * file.
	 */
	if ((error = VOP_ACCESS(vp, VADMIN, cred, p)))
		return (error);

	/*
	 * To change the owner of a file, or change the group of a file to a
	 * group of which we are not a member, the caller must have
	 * privilege.
	 */
	if ((uid != node->tn_uid ||
	    (gid != node->tn_gid && !groupmember(gid, cred))) &&
	    (error = priv_check_cred(cred, PRIV_VFS_CHOWN, 0)))
		return (error);

	ogid = node->tn_gid;
	ouid = node->tn_uid;

	node->tn_uid = uid;
	node->tn_gid = gid;

	node->tn_status |= TMPFS_NODE_CHANGED;

	if ((node->tn_mode & (S_ISUID | S_ISGID)) && (ouid != uid || ogid != gid)) {
		if (priv_check_cred(cred, PRIV_VFS_RETAINSUGID, 0))
			node->tn_mode &= ~(S_ISUID | S_ISGID);
	}

	MPASS(VOP_ISLOCKED(vp, p));

	return 0;
}

/* --------------------------------------------------------------------- */

/*
 * Change size of the given vnode.
 * Caller should execute tmpfs_update on vp after a successful execution.
 * The vnode must be locked on entry and remain locked on exit.
 */
int
tmpfs_chsize(struct vnode *vp, u_quad_t size, struct ucred *cred,
    struct thread *p)
{
	int error;
	struct tmpfs_node *node;

	MPASS(VOP_ISLOCKED(vp, p));

	node = VP_TO_TMPFS_NODE(vp);

	/* Decide whether this is a valid operation based on the file type. */
	error = 0;
	switch (vp->v_type) {
	case VDIR:
		return EISDIR;

	case VREG:
		if (vp->v_mount->mnt_flag & MNT_RDONLY)
			return EROFS;
		break;

	case VBLK:
		/* FALLTHROUGH */
	case VCHR:
		/* FALLTHROUGH */
	case VFIFO:
		/* Allow modifications of special files even if in the file
		 * system is mounted read-only (we are not modifying the
		 * files themselves, but the objects they represent). */
		return 0;

	default:
		/* Anything else is unsupported. */
		return EOPNOTSUPP;
	}

	/* Immutable or append-only files cannot be modified, either. */
	if (node->tn_flags & (IMMUTABLE | APPEND))
		return EPERM;

	error = tmpfs_truncate(vp, size);
	/* tmpfs_truncate will raise the NOTE_EXTEND and NOTE_ATTRIB kevents
	 * for us, as will update tn_status; no need to do that here. */

	MPASS(VOP_ISLOCKED(vp, p));

	return error;
}

/* --------------------------------------------------------------------- */

/*
 * Change access and modification times of the given vnode.
 * Caller should execute tmpfs_update on vp after a successful execution.
 * The vnode must be locked on entry and remain locked on exit.
 */
int
tmpfs_chtimes(struct vnode *vp, struct timespec *atime, struct timespec *mtime,
	struct timespec *birthtime, int vaflags, struct ucred *cred, struct thread *l)
{
	int error;
	struct tmpfs_node *node;

	MPASS(VOP_ISLOCKED(vp, l));

	node = VP_TO_TMPFS_NODE(vp);

	/* Disallow this operation if the file system is mounted read-only. */
	if (vp->v_mount->mnt_flag & MNT_RDONLY)
		return EROFS;

	/* Immutable or append-only files cannot be modified, either. */
	if (node->tn_flags & (IMMUTABLE | APPEND))
		return EPERM;

	/* Determine if the user have proper privilege to update time. */
	if (vaflags & VA_UTIMES_NULL) {
		error = VOP_ACCESS(vp, VADMIN, cred, l);
		if (error)
			error = VOP_ACCESS(vp, VWRITE, cred, l);
	} else
		error = VOP_ACCESS(vp, VADMIN, cred, l);
	if (error)
		return (error);

	if (atime->tv_sec != VNOVAL && atime->tv_nsec != VNOVAL)
		node->tn_status |= TMPFS_NODE_ACCESSED;

	if (mtime->tv_sec != VNOVAL && mtime->tv_nsec != VNOVAL)
		node->tn_status |= TMPFS_NODE_MODIFIED;

	if (birthtime->tv_nsec != VNOVAL && birthtime->tv_nsec != VNOVAL)
		node->tn_status |= TMPFS_NODE_MODIFIED;

	tmpfs_itimes(vp, atime, mtime);

	if (birthtime->tv_nsec != VNOVAL && birthtime->tv_nsec != VNOVAL)
		node->tn_birthtime = *birthtime;
	MPASS(VOP_ISLOCKED(vp, l));

	return 0;
}

/* --------------------------------------------------------------------- */
/* Sync timestamps */
void
tmpfs_itimes(struct vnode *vp, const struct timespec *acc,
    const struct timespec *mod)
{
	struct tmpfs_node *node;
	struct timespec now;

	node = VP_TO_TMPFS_NODE(vp);

	if ((node->tn_status & (TMPFS_NODE_ACCESSED | TMPFS_NODE_MODIFIED |
	    TMPFS_NODE_CHANGED)) == 0)
		return;

	vfs_timestamp(&now);
	if (node->tn_status & TMPFS_NODE_ACCESSED) {
		if (acc == NULL)
			 acc = &now;
		node->tn_atime = *acc;
	}
	if (node->tn_status & TMPFS_NODE_MODIFIED) {
		if (mod == NULL)
			mod = &now;
		node->tn_mtime = *mod;
	}
	if (node->tn_status & TMPFS_NODE_CHANGED) {
		node->tn_ctime = now;
	}
	node->tn_status &=
	    ~(TMPFS_NODE_ACCESSED | TMPFS_NODE_MODIFIED | TMPFS_NODE_CHANGED);
}

/* --------------------------------------------------------------------- */

void
tmpfs_update(struct vnode *vp)
{

	tmpfs_itimes(vp, NULL, NULL);
}

/* --------------------------------------------------------------------- */

int
tmpfs_truncate(struct vnode *vp, off_t length)
{
	boolean_t extended;
	int error;
	struct tmpfs_node *node;

	node = VP_TO_TMPFS_NODE(vp);
	extended = length > node->tn_size;

	if (length < 0) {
		error = EINVAL;
		goto out;
	}

	if (node->tn_size == length) {
		error = 0;
		goto out;
	}

	if (length > VFS_TO_TMPFS(vp->v_mount)->tm_maxfilesize)
		return (EFBIG);

	error = tmpfs_reg_resize(vp, length);
	if (error == 0) {
		node->tn_status |= TMPFS_NODE_CHANGED | TMPFS_NODE_MODIFIED;
	}

out:
	tmpfs_update(vp);

	return error;
}