/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 2014 The FreeBSD Foundation
 *
 * This software was developed by Edward Tomasz Napierala under sponsorship
 * from the FreeBSD Foundation.
 *
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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.
 *
 */

#include <sys/cdefs.h>
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/condvar.h>
#include <sys/dirent.h>
#include <sys/fcntl.h>
#include <sys/lock.h>
#include <sys/mount.h>
#include <sys/mutex.h>
#include <sys/namei.h>
#include <sys/signalvar.h>
#include <sys/stat.h>
#include <sys/taskqueue.h>
#include <sys/tree.h>
#include <sys/vnode.h>
#include <machine/atomic.h>
#include <vm/uma.h>

#include <fs/autofs/autofs.h>

static int	autofs_trigger_vn(struct vnode *vp, const char *path,
		    int pathlen, struct vnode **newvp);

extern struct autofs_softc	*autofs_softc;

static int
autofs_access(struct vop_access_args *ap)
{

	/*
	 * Nothing to do here; the only kind of access control
	 * needed is in autofs_mkdir().
	 */

	return (0);
}

static int
autofs_getattr(struct vop_getattr_args *ap)
{
	struct vnode *vp, *newvp;
	struct autofs_node *anp;
	struct mount *mp;
	struct vattr *vap;
	int error;

	vp = ap->a_vp;
	anp = vp->v_data;
	mp = vp->v_mount;
	vap = ap->a_vap;

	KASSERT(ap->a_vp->v_type == VDIR, ("!VDIR"));

	/*
	 * The reason we must do this is that some tree-walking software,
	 * namely fts(3), assumes that stat(".") results will not change
	 * between chdir("subdir") and chdir(".."), and fails with ENOENT
	 * otherwise.
	 */
	if (autofs_mount_on_stat && autofs_cached(anp, NULL, 0) == false &&
	    autofs_ignore_thread(curthread) == false) {
		error = autofs_trigger_vn(vp, "", 0, &newvp);
		if (error != 0)
			return (error);

		if (newvp != NULL) {
			error = VOP_GETATTR(newvp, ap->a_vap,
			    ap->a_cred);
			vput(newvp);
			return (error);
		}
	}

	vap->va_type = VDIR;
	vap->va_mode = 0755;
	vap->va_nlink = 3; /* XXX */
	vap->va_uid = 0;
	vap->va_gid = 0;
	vap->va_rdev = NODEV;
	vap->va_fsid = mp->mnt_stat.f_fsid.val[0];
	vap->va_fileid = anp->an_fileno;
	vap->va_size = S_BLKSIZE;
	vap->va_blocksize = S_BLKSIZE;
	vap->va_mtime = anp->an_ctime;
	vap->va_atime = anp->an_ctime;
	vap->va_ctime = anp->an_ctime;
	vap->va_birthtime = anp->an_ctime;
	vap->va_gen = 0;
	vap->va_flags = 0;
	vap->va_rdev = 0;
	vap->va_bytes = S_BLKSIZE;
	vap->va_filerev = 0;
	vap->va_spare = 0;

	return (0);
}

/*
 * Unlock the vnode, request automountd(8) action, and then lock it back.
 * If anything got mounted on top of the vnode, return the new filesystem's
 * root vnode in 'newvp', locked.
 */
static int
autofs_trigger_vn(struct vnode *vp, const char *path, int pathlen,
    struct vnode **newvp)
{
	struct autofs_node *anp;
	int error, lock_flags;

	anp = vp->v_data;

	/*
	 * Release the vnode lock, so that other operations, in partcular
	 * mounting a filesystem on top of it, can proceed.  Increase use
	 * count, to prevent the vnode from being deallocated and to prevent
	 * filesystem from being unmounted.
	 */
	lock_flags = VOP_ISLOCKED(vp);
	vref(vp);
	VOP_UNLOCK(vp);

	sx_xlock(&autofs_softc->sc_lock);

	/*
	 * XXX: Workaround for mounting the same thing multiple times; revisit.
	 */
	if (vp->v_mountedhere != NULL) {
		error = 0;
		goto mounted;
	}

	error = autofs_trigger(anp, path, pathlen);
mounted:
	sx_xunlock(&autofs_softc->sc_lock);
	vn_lock(vp, lock_flags | LK_RETRY);
	vunref(vp);
	if (VN_IS_DOOMED(vp)) {
		AUTOFS_DEBUG("VIRF_DOOMED");
		return (ENOENT);
	}

	if (error != 0)
		return (error);

	if (vp->v_mountedhere == NULL) {
		*newvp = NULL;
		return (0);
	} else {
		/*
		 * If the operation that succeeded was mount, then mark
		 * the node as non-cached.  Otherwise, if someone unmounts
		 * the filesystem before the cache times out, we will fail
		 * to trigger.
		 */
		anp->an_cached = false;
	}

	error = VFS_ROOT(vp->v_mountedhere, lock_flags, newvp);
	if (error != 0) {
		AUTOFS_WARN("VFS_ROOT() failed with error %d", error);
		return (error);
	}

	return (0);
}

static int
autofs_vget_callback(struct mount *mp, void *arg, int flags,
    struct vnode **vpp)
{

	return (autofs_node_vn(arg, mp, flags, vpp));
}

static int
autofs_lookup(struct vop_lookup_args *ap)
{
	struct vnode *dvp, *newvp, **vpp;
	struct mount *mp;
	struct autofs_mount *amp;
	struct autofs_node *anp, *child;
	struct componentname *cnp;
	int error;

	dvp = ap->a_dvp;
	vpp = ap->a_vpp;
	mp = dvp->v_mount;
	amp = VFSTOAUTOFS(mp);
	anp = dvp->v_data;
	cnp = ap->a_cnp;

	if (cnp->cn_flags & ISDOTDOT) {
		KASSERT(anp->an_parent != NULL, ("NULL parent"));
		/*
		 * Note that in this case, dvp is the child vnode, and we
		 * are looking up the parent vnode - exactly reverse from
		 * normal operation.  Unlocking dvp requires some rather
		 * tricky unlock/relock dance to prevent mp from being freed;
		 * use vn_vget_ino_gen() which takes care of all that.
		 */
		error = vn_vget_ino_gen(dvp, autofs_vget_callback,
		    anp->an_parent, cnp->cn_lkflags, vpp);
		if (error != 0) {
			AUTOFS_WARN("vn_vget_ino_gen() failed with error %d",
			    error);
			return (error);
		}
		return (error);
	}

	if (cnp->cn_namelen == 1 && cnp->cn_nameptr[0] == '.') {
		vref(dvp);
		*vpp = dvp;

		return (0);
	}

	if (autofs_cached(anp, cnp->cn_nameptr, cnp->cn_namelen) == false &&
	    autofs_ignore_thread(cnp->cn_thread) == false) {
		error = autofs_trigger_vn(dvp,
		    cnp->cn_nameptr, cnp->cn_namelen, &newvp);
		if (error != 0)
			return (error);

		if (newvp != NULL) {
			/*
			 * The target filesystem got automounted.
			 * Let the lookup(9) go around with the same
			 * path component.
			 */
			vput(newvp);
			return (ERELOOKUP);
		}
	}

	AUTOFS_SLOCK(amp);
	error = autofs_node_find(anp, cnp->cn_nameptr, cnp->cn_namelen, &child);
	if (error != 0) {
		if ((cnp->cn_flags & ISLASTCN) && cnp->cn_nameiop == CREATE) {
			AUTOFS_SUNLOCK(amp);
			return (EJUSTRETURN);
		}

		AUTOFS_SUNLOCK(amp);
		return (ENOENT);
	}

	/*
	 * XXX: Dropping the node here is ok, because we never remove nodes.
	 */
	AUTOFS_SUNLOCK(amp);

	error = autofs_node_vn(child, mp, cnp->cn_lkflags, vpp);
	if (error != 0) {
		if ((cnp->cn_flags & ISLASTCN) && cnp->cn_nameiop == CREATE)
			return (EJUSTRETURN);

		return (error);
	}

	return (0);
}

static int
autofs_mkdir(struct vop_mkdir_args *ap)
{
	struct vnode *vp;
	struct autofs_node *anp;
	struct autofs_mount *amp;
	struct autofs_node *child;
	int error;

	vp = ap->a_dvp;
	anp = vp->v_data;
	amp = VFSTOAUTOFS(vp->v_mount);

	/*
	 * Do not allow mkdir() if the calling thread is not
	 * automountd(8) descendant.
	 */
	if (autofs_ignore_thread(curthread) == false)
		return (EPERM);

	AUTOFS_XLOCK(amp);
	error = autofs_node_new(anp, amp, ap->a_cnp->cn_nameptr,
	    ap->a_cnp->cn_namelen, &child);
	if (error != 0) {
		AUTOFS_XUNLOCK(amp);
		return (error);
	}
	AUTOFS_XUNLOCK(amp);

	error = autofs_node_vn(child, vp->v_mount, LK_EXCLUSIVE, ap->a_vpp);

	return (error);
}

static int
autofs_print(struct vop_print_args *ap)
{
	struct vnode *vp;
	struct autofs_node *anp;

	vp = ap->a_vp;
	anp = vp->v_data;

	printf("    name \"%s\", fileno %d, cached %d, wildcards %d\n",
	    anp->an_name, anp->an_fileno, anp->an_cached, anp->an_wildcards);

	return (0);
}

/*
 * Write out a single 'struct dirent', based on 'name' and 'fileno' arguments.
 */
static int
autofs_readdir_one(struct uio *uio, const char *name, int fileno,
    size_t *reclenp)
{
	struct dirent dirent;
	size_t namlen, reclen;
	int error;

	namlen = strlen(name);
	reclen = _GENERIC_DIRLEN(namlen);
	if (reclenp != NULL)
		*reclenp = reclen;

	if (uio == NULL)
		return (0);

	if (uio->uio_resid < reclen)
		return (EINVAL);

	dirent.d_fileno = fileno;
	dirent.d_off = uio->uio_offset + reclen;
	dirent.d_reclen = reclen;
	dirent.d_type = DT_DIR;
	dirent.d_namlen = namlen;
	memcpy(dirent.d_name, name, namlen);
	dirent_terminate(&dirent);
	error = uiomove(&dirent, reclen, uio);

	return (error);
}

static size_t
autofs_dirent_reclen(const char *name)
{
	size_t reclen;

	(void)autofs_readdir_one(NULL, name, -1, &reclen);

	return (reclen);
}

static int
autofs_readdir(struct vop_readdir_args *ap)
{
	struct vnode *vp, *newvp;
	struct autofs_mount *amp;
	struct autofs_node *anp, *child;
	struct uio *uio;
	size_t reclen, reclens;
	ssize_t initial_resid;
	int error;

	vp = ap->a_vp;
	amp = VFSTOAUTOFS(vp->v_mount);
	anp = vp->v_data;
	uio = ap->a_uio;
	initial_resid = ap->a_uio->uio_resid;

	KASSERT(vp->v_type == VDIR, ("!VDIR"));

	if (autofs_cached(anp, NULL, 0) == false &&
	    autofs_ignore_thread(curthread) == false) {
		error = autofs_trigger_vn(vp, "", 0, &newvp);
		if (error != 0)
			return (error);

		if (newvp != NULL) {
			error = VOP_READDIR(newvp, ap->a_uio, ap->a_cred,
			    ap->a_eofflag, ap->a_ncookies, ap->a_cookies);
			vput(newvp);
			return (error);
		}
	}

	if (uio->uio_offset < 0)
		return (EINVAL);

	if (ap->a_eofflag != NULL)
		*ap->a_eofflag = FALSE;

	/*
	 * Write out the directory entry for ".".  This is conditional
	 * on the current offset into the directory; same applies to the
	 * other two cases below.
	 */
	if (uio->uio_offset == 0) {
		error = autofs_readdir_one(uio, ".", anp->an_fileno, &reclen);
		if (error != 0)
			goto out;
	}
	reclens = autofs_dirent_reclen(".");

	/*
	 * Write out the directory entry for "..".
	 */
	if (uio->uio_offset <= reclens) {
		if (uio->uio_offset != reclens)
			return (EINVAL);
		if (anp->an_parent == NULL) {
			error = autofs_readdir_one(uio, "..",
			    anp->an_fileno, &reclen);
		} else {
			error = autofs_readdir_one(uio, "..",
			    anp->an_parent->an_fileno, &reclen);
		}
		if (error != 0)
			goto out;
	}

	reclens += autofs_dirent_reclen("..");

	/*
	 * Write out the directory entries for subdirectories.
	 */
	AUTOFS_SLOCK(amp);
	RB_FOREACH(child, autofs_node_tree, &anp->an_children) {
		/*
		 * Check the offset to skip entries returned by previous
		 * calls to getdents().
		 */
		if (uio->uio_offset > reclens) {
			reclens += autofs_dirent_reclen(child->an_name);
			continue;
		}

		/*
		 * Prevent seeking into the middle of dirent.
		 */
		if (uio->uio_offset != reclens) {
			AUTOFS_SUNLOCK(amp);
			return (EINVAL);
		}

		error = autofs_readdir_one(uio, child->an_name,
		    child->an_fileno, &reclen);
		reclens += reclen;
		if (error != 0) {
			AUTOFS_SUNLOCK(amp);
			goto out;
		}
	}
	AUTOFS_SUNLOCK(amp);

	if (ap->a_eofflag != NULL)
		*ap->a_eofflag = TRUE;

	return (0);

out:
	/*
	 * Return error if the initial buffer was too small to do anything.
	 */
	if (uio->uio_resid == initial_resid)
		return (error);

	/*
	 * Don't return an error if we managed to copy out some entries.
	 */
	if (uio->uio_resid < reclen)
		return (0);

	return (error);
}

static int
autofs_reclaim(struct vop_reclaim_args *ap)
{
	struct vnode *vp;
	struct autofs_node *anp;

	vp = ap->a_vp;
	anp = vp->v_data;

	/*
	 * We do not free autofs_node here; instead we are
	 * destroying them in autofs_node_delete().
	 */
	sx_xlock(&anp->an_vnode_lock);
	anp->an_vnode = NULL;
	vp->v_data = NULL;
	sx_xunlock(&anp->an_vnode_lock);

	return (0);
}

struct vop_vector autofs_vnodeops = {
	.vop_default =		&default_vnodeops,

	.vop_access =		autofs_access,
	.vop_lookup =		autofs_lookup,
	.vop_create =		VOP_EOPNOTSUPP,
	.vop_getattr =		autofs_getattr,
	.vop_link =		VOP_EOPNOTSUPP,
	.vop_mkdir =		autofs_mkdir,
	.vop_mknod =		VOP_EOPNOTSUPP,
	.vop_print =		autofs_print,
	.vop_read =		VOP_EOPNOTSUPP,
	.vop_readdir =		autofs_readdir,
	.vop_remove =		VOP_EOPNOTSUPP,
	.vop_rename =		VOP_EOPNOTSUPP,
	.vop_rmdir =		VOP_EOPNOTSUPP,
	.vop_setattr =		VOP_EOPNOTSUPP,
	.vop_symlink =		VOP_EOPNOTSUPP,
	.vop_write =		VOP_EOPNOTSUPP,
	.vop_reclaim =		autofs_reclaim,
};
VFS_VOP_VECTOR_REGISTER(autofs_vnodeops);

int
autofs_node_new(struct autofs_node *parent, struct autofs_mount *amp,
    const char *name, int namelen, struct autofs_node **anpp)
{
	struct autofs_node *anp;

	if (parent != NULL) {
		AUTOFS_ASSERT_XLOCKED(parent->an_mount);

		KASSERT(autofs_node_find(parent, name, namelen, NULL) == ENOENT,
		    ("node \"%s\" already exists", name));
	}

	anp = uma_zalloc(autofs_node_zone, M_WAITOK | M_ZERO);
	if (namelen >= 0)
		anp->an_name = strndup(name, namelen, M_AUTOFS);
	else
		anp->an_name = strdup(name, M_AUTOFS);
	anp->an_fileno = atomic_fetchadd_int(&amp->am_last_fileno, 1);
	callout_init(&anp->an_callout, 1);
	/*
	 * The reason for SX_NOWITNESS here is that witness(4)
	 * cannot tell vnodes apart, so the following perfectly
	 * valid lock order...
	 *
	 * vnode lock A -> autofsvlk B -> vnode lock B
	 *
	 * ... gets reported as a LOR.
	 */
	sx_init_flags(&anp->an_vnode_lock, "autofsvlk", SX_NOWITNESS);
	getnanotime(&anp->an_ctime);
	anp->an_parent = parent;
	anp->an_mount = amp;
	if (parent != NULL)
		RB_INSERT(autofs_node_tree, &parent->an_children, anp);
	RB_INIT(&anp->an_children);

	*anpp = anp;
	return (0);
}

int
autofs_node_find(struct autofs_node *parent, const char *name,
    int namelen, struct autofs_node **anpp)
{
	struct autofs_node *anp, find;
	int error;

	AUTOFS_ASSERT_LOCKED(parent->an_mount);

	if (namelen >= 0)
		find.an_name = strndup(name, namelen, M_AUTOFS);
	else
		find.an_name = strdup(name, M_AUTOFS);

	anp = RB_FIND(autofs_node_tree, &parent->an_children, &find);
	if (anp != NULL) {
		error = 0;
		if (anpp != NULL)
			*anpp = anp;
	} else {
		error = ENOENT;
	}

	free(find.an_name, M_AUTOFS);

	return (error);
}

void
autofs_node_delete(struct autofs_node *anp)
{
	struct autofs_node *parent;

	AUTOFS_ASSERT_XLOCKED(anp->an_mount);
	KASSERT(RB_EMPTY(&anp->an_children), ("have children"));

	callout_drain(&anp->an_callout);

	parent = anp->an_parent;
	if (parent != NULL)
		RB_REMOVE(autofs_node_tree, &parent->an_children, anp);
	sx_destroy(&anp->an_vnode_lock);
	free(anp->an_name, M_AUTOFS);
	uma_zfree(autofs_node_zone, anp);
}

int
autofs_node_vn(struct autofs_node *anp, struct mount *mp, int flags,
    struct vnode **vpp)
{
	struct vnode *vp;
	int error;

	AUTOFS_ASSERT_UNLOCKED(anp->an_mount);

	sx_xlock(&anp->an_vnode_lock);

	vp = anp->an_vnode;
	if (vp != NULL) {
		error = vget(vp, flags | LK_RETRY);
		if (error != 0) {
			AUTOFS_WARN("vget failed with error %d", error);
			sx_xunlock(&anp->an_vnode_lock);
			return (error);
		}
		if (VN_IS_DOOMED(vp)) {
			/*
			 * We got forcibly unmounted.
			 */
			AUTOFS_DEBUG("doomed vnode");
			sx_xunlock(&anp->an_vnode_lock);
			vput(vp);

			return (ENOENT);
		}

		*vpp = vp;
		sx_xunlock(&anp->an_vnode_lock);
		return (0);
	}

	error = getnewvnode("autofs", mp, &autofs_vnodeops, &vp);
	if (error != 0) {
		sx_xunlock(&anp->an_vnode_lock);
		return (error);
	}

	error = vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
	if (error != 0) {
		sx_xunlock(&anp->an_vnode_lock);
		vdrop(vp);
		return (error);
	}

	vp->v_type = VDIR;
	if (anp->an_parent == NULL)
		vp->v_vflag |= VV_ROOT;
	vp->v_data = anp;

	VN_LOCK_ASHARE(vp);

	error = insmntque(vp, mp);
	if (error != 0) {
		AUTOFS_DEBUG("insmntque() failed with error %d", error);
		sx_xunlock(&anp->an_vnode_lock);
		return (error);
	}

	KASSERT(anp->an_vnode == NULL, ("lost race"));
	anp->an_vnode = vp;

	sx_xunlock(&anp->an_vnode_lock);

	*vpp = vp;
	return (0);
}