freebsd-dev/contrib/lib9p/request.c

/*
 * Copyright 2016 Jakub Klama <jceel@FreeBSD.org>
 * All rights reserved
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted providing 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 ``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 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 <stdlib.h>
#include <string.h>
#include <assert.h>
#include <errno.h>
#include <sys/param.h>
#include <sys/uio.h>
#if defined(__FreeBSD__)
#include <sys/sbuf.h>
#else
#include "sbuf/sbuf.h"
#endif
#include "lib9p.h"
#include "lib9p_impl.h"
#include "fcall.h"
#include "fid.h"
#include "hashtable.h"
#include "log.h"
#include "linux_errno.h"
#include "backend/backend.h"
#include "threadpool.h"

#define N(x)    (sizeof(x) / sizeof(x[0]))

static int l9p_dispatch_tversion(struct l9p_request *req);
static int l9p_dispatch_tattach(struct l9p_request *req);
static int l9p_dispatch_tclunk(struct l9p_request *req);
static int l9p_dispatch_tcreate(struct l9p_request *req);
static int l9p_dispatch_topen(struct l9p_request *req);
static int l9p_dispatch_tread(struct l9p_request *req);
static int l9p_dispatch_tremove(struct l9p_request *req);
static int l9p_dispatch_tstat(struct l9p_request *req);
static int l9p_dispatch_twalk(struct l9p_request *req);
static int l9p_dispatch_twrite(struct l9p_request *req);
static int l9p_dispatch_twstat(struct l9p_request *req);
static int l9p_dispatch_tstatfs(struct l9p_request *req);
static int l9p_dispatch_tlopen(struct l9p_request *req);
static int l9p_dispatch_tlcreate(struct l9p_request *req);
static int l9p_dispatch_tsymlink(struct l9p_request *req);
static int l9p_dispatch_tmknod(struct l9p_request *req);
static int l9p_dispatch_trename(struct l9p_request *req);
static int l9p_dispatch_treadlink(struct l9p_request *req);
static int l9p_dispatch_tgetattr(struct l9p_request *req);
static int l9p_dispatch_tsetattr(struct l9p_request *req);
static int l9p_dispatch_txattrwalk(struct l9p_request *req);
static int l9p_dispatch_txattrcreate(struct l9p_request *req);
static int l9p_dispatch_treaddir(struct l9p_request *req);
static int l9p_dispatch_tfsync(struct l9p_request *req);
static int l9p_dispatch_tlock(struct l9p_request *req);
static int l9p_dispatch_tgetlock(struct l9p_request *req);
static int l9p_dispatch_tlink(struct l9p_request *req);
static int l9p_dispatch_tmkdir(struct l9p_request *req);
static int l9p_dispatch_trenameat(struct l9p_request *req);
static int l9p_dispatch_tunlinkat(struct l9p_request *req);

/*
 * Each Txxx handler has a "must run" flag.  If it is false,
 * we check for a flush request before calling the handler.
 * If a flush is already requested we can instantly fail the
 * request with EINTR.
 *
 * Tclunk and Tremove must run because they make their fids
 * become invalid.  Tversion and Tattach should never get
 * a flush request applied (it makes no sense as the connection
 * is not really running yet), so it should be harmless to
 * set them either way, but for now we have them as must-run.
 * Flushing a Tflush is not really allowed either so we keep
 * these as must-run too (although they run without being done
 * threaded anyway).
 */
struct l9p_handler {
	enum l9p_ftype type;
	int (*handler)(struct l9p_request *);
	bool must_run;
};

static const struct l9p_handler l9p_handlers_no_version[] = {
	{L9P_TVERSION, l9p_dispatch_tversion, true},
};

static const struct l9p_handler l9p_handlers_base[] = {
	{L9P_TVERSION, l9p_dispatch_tversion, true},
	{L9P_TATTACH, l9p_dispatch_tattach, true},
	{L9P_TCLUNK, l9p_dispatch_tclunk, true},
	{L9P_TFLUSH, l9p_threadpool_tflush, true},
	{L9P_TCREATE, l9p_dispatch_tcreate, false},
	{L9P_TOPEN, l9p_dispatch_topen, false},
	{L9P_TREAD, l9p_dispatch_tread, false},
	{L9P_TWRITE, l9p_dispatch_twrite, false},
	{L9P_TREMOVE, l9p_dispatch_tremove, true},
	{L9P_TSTAT, l9p_dispatch_tstat, false},
	{L9P_TWALK, l9p_dispatch_twalk, false},
	{L9P_TWSTAT, l9p_dispatch_twstat, false}
};
static const struct l9p_handler l9p_handlers_dotu[] = {
	{L9P_TVERSION, l9p_dispatch_tversion, true},
	{L9P_TATTACH, l9p_dispatch_tattach, true},
	{L9P_TCLUNK, l9p_dispatch_tclunk, true},
	{L9P_TFLUSH, l9p_threadpool_tflush, true},
	{L9P_TCREATE, l9p_dispatch_tcreate, false},
	{L9P_TOPEN, l9p_dispatch_topen, false},
	{L9P_TREAD, l9p_dispatch_tread, false},
	{L9P_TWRITE, l9p_dispatch_twrite, false},
	{L9P_TREMOVE, l9p_dispatch_tremove, true},
	{L9P_TSTAT, l9p_dispatch_tstat, false},
	{L9P_TWALK, l9p_dispatch_twalk, false},
	{L9P_TWSTAT, l9p_dispatch_twstat, false}
};
static const struct l9p_handler l9p_handlers_dotL[] = {
	{L9P_TVERSION, l9p_dispatch_tversion, true},
	{L9P_TATTACH, l9p_dispatch_tattach, true},
	{L9P_TCLUNK, l9p_dispatch_tclunk, true},
	{L9P_TFLUSH, l9p_threadpool_tflush, true},
	{L9P_TCREATE, l9p_dispatch_tcreate, false},
	{L9P_TOPEN, l9p_dispatch_topen, false},
	{L9P_TREAD, l9p_dispatch_tread, false},
	{L9P_TWRITE, l9p_dispatch_twrite, false},
	{L9P_TREMOVE, l9p_dispatch_tremove, true},
	{L9P_TSTAT, l9p_dispatch_tstat, false},
	{L9P_TWALK, l9p_dispatch_twalk, false},
	{L9P_TWSTAT, l9p_dispatch_twstat, false},
	{L9P_TSTATFS, l9p_dispatch_tstatfs, false},
	{L9P_TLOPEN, l9p_dispatch_tlopen, false},
	{L9P_TLCREATE, l9p_dispatch_tlcreate, false},
	{L9P_TSYMLINK, l9p_dispatch_tsymlink, false},
	{L9P_TMKNOD, l9p_dispatch_tmknod, false},
	{L9P_TRENAME, l9p_dispatch_trename, false},
	{L9P_TREADLINK, l9p_dispatch_treadlink, false},
	{L9P_TGETATTR, l9p_dispatch_tgetattr, false},
	{L9P_TSETATTR, l9p_dispatch_tsetattr, false},
	{L9P_TXATTRWALK, l9p_dispatch_txattrwalk, false},
	{L9P_TXATTRCREATE, l9p_dispatch_txattrcreate, false},
	{L9P_TREADDIR, l9p_dispatch_treaddir, false},
	{L9P_TFSYNC, l9p_dispatch_tfsync, false},
	{L9P_TLOCK, l9p_dispatch_tlock, true},
	{L9P_TGETLOCK, l9p_dispatch_tgetlock, true},
	{L9P_TLINK, l9p_dispatch_tlink, false},
	{L9P_TMKDIR, l9p_dispatch_tmkdir, false},
	{L9P_TRENAMEAT, l9p_dispatch_trenameat, false},
	{L9P_TUNLINKAT, l9p_dispatch_tunlinkat, false},
};

/*
 * NB: version index 0 is reserved for new connections, and
 * is a protocol that handles only L9P_TVERSION.  Once we get a
 * valid version, we start a new session using its dispatch table.
 */
static const struct {
	const char *name;
	const struct l9p_handler *handlers;
	int n_handlers;
} l9p_versions[] = {
	{ "<none>", l9p_handlers_no_version, N(l9p_handlers_no_version) },
	{ "9P2000", l9p_handlers_base, N(l9p_handlers_base) },
	{ "9P2000.u", l9p_handlers_dotu, N(l9p_handlers_dotu), },
	{ "9P2000.L", l9p_handlers_dotL, N(l9p_handlers_dotL), },
};

/*
 * Run the appropriate handler for this request.
 * It's our caller's responsibility to respond.
 */
int
l9p_dispatch_request(struct l9p_request *req)
{
	struct l9p_connection *conn;
#if defined(L9P_DEBUG)
	struct sbuf *sb;
#endif
	size_t i, n;
	const struct l9p_handler *handlers, *hp;
	bool flush_requested;

	conn = req->lr_conn;
	flush_requested = req->lr_flushstate == L9P_FLUSH_REQUESTED_PRE_START;

	handlers = l9p_versions[conn->lc_version].handlers;
	n = (size_t)l9p_versions[conn->lc_version].n_handlers;
	for (hp = handlers, i = 0; i < n; hp++, i++)
		if (req->lr_req.hdr.type == hp->type)
			goto found;
	hp = NULL;
found:

#if defined(L9P_DEBUG)
	sb = sbuf_new_auto();
	if (flush_requested) {
		sbuf_cat(sb, "FLUSH requested pre-dispatch");
		if (hp != NULL && hp->must_run)
			sbuf_cat(sb, ", but must run");
		sbuf_cat(sb, ": ");
	}
	l9p_describe_fcall(&req->lr_req, conn->lc_version, sb);
	sbuf_finish(sb);

	L9P_LOG(L9P_DEBUG, "%s", sbuf_data(sb));
	sbuf_delete(sb);
#endif

	if (hp != NULL) {
		if (!flush_requested || hp->must_run)
			return (hp->handler(req));
		return (EINTR);
	}

	L9P_LOG(L9P_WARNING, "unknown request of type %d",
	    req->lr_req.hdr.type);
	return (ENOSYS);
}

/*
 * Translate BSD errno to 9P2000/9P2000.u errno.
 */
static inline int
e29p(int errnum)
{
	static int const table[] = {
		[ENOTEMPTY] = EPERM,
		[EDQUOT] = EPERM,
		[ENOSYS] = EPERM,	/* ??? */
	};

	if ((size_t)errnum < N(table) && table[errnum] != 0)
		return (table[errnum]);
	if (errnum <= ERANGE)
		return (errnum);
	return (EIO);			/* ??? */
}

/*
 * Translate BSD errno to Linux errno.
 */
static inline int
e2linux(int errnum)
{
	static int const table[] = {
		[EDEADLK] = LINUX_EDEADLK,
		[EAGAIN] = LINUX_EAGAIN,
		[EINPROGRESS] = LINUX_EINPROGRESS,
		[EALREADY] = LINUX_EALREADY,
		[ENOTSOCK] = LINUX_ENOTSOCK,
		[EDESTADDRREQ] = LINUX_EDESTADDRREQ,
		[EMSGSIZE] = LINUX_EMSGSIZE,
		[EPROTOTYPE] = LINUX_EPROTOTYPE,
		[ENOPROTOOPT] = LINUX_ENOPROTOOPT,
		[EPROTONOSUPPORT] = LINUX_EPROTONOSUPPORT,
		[ESOCKTNOSUPPORT] = LINUX_ESOCKTNOSUPPORT,
		[EOPNOTSUPP] = LINUX_EOPNOTSUPP,
		[EPFNOSUPPORT] = LINUX_EPFNOSUPPORT,
		[EAFNOSUPPORT] = LINUX_EAFNOSUPPORT,
		[EADDRINUSE] = LINUX_EADDRINUSE,
		[EADDRNOTAVAIL] = LINUX_EADDRNOTAVAIL,
		[ENETDOWN] = LINUX_ENETDOWN,
		[ENETUNREACH] = LINUX_ENETUNREACH,
		[ENETRESET] = LINUX_ENETRESET,
		[ECONNABORTED] = LINUX_ECONNABORTED,
		[ECONNRESET] = LINUX_ECONNRESET,
		[ENOBUFS] = LINUX_ENOBUFS,
		[EISCONN] = LINUX_EISCONN,
		[ENOTCONN] = LINUX_ENOTCONN,
		[ESHUTDOWN] = LINUX_ESHUTDOWN,
		[ETOOMANYREFS] = LINUX_ETOOMANYREFS,
		[ETIMEDOUT] = LINUX_ETIMEDOUT,
		[ECONNREFUSED] = LINUX_ECONNREFUSED,
		[ELOOP] = LINUX_ELOOP,
		[ENAMETOOLONG] = LINUX_ENAMETOOLONG,
		[EHOSTDOWN] = LINUX_EHOSTDOWN,
		[EHOSTUNREACH] = LINUX_EHOSTUNREACH,
		[ENOTEMPTY] = LINUX_ENOTEMPTY,
		[EPROCLIM] = LINUX_EAGAIN,
		[EUSERS] = LINUX_EUSERS,
		[EDQUOT] = LINUX_EDQUOT,
		[ESTALE] = LINUX_ESTALE,
		[EREMOTE] = LINUX_EREMOTE,
		/* EBADRPC = unmappable? */
		/* ERPCMISMATCH = unmappable? */
		/* EPROGUNAVAIL = unmappable? */
		/* EPROGMISMATCH = unmappable? */
		/* EPROCUNAVAIL = unmappable? */
		[ENOLCK] = LINUX_ENOLCK,
		[ENOSYS] = LINUX_ENOSYS,
		/* EFTYPE = unmappable? */
		/* EAUTH = unmappable? */
		/* ENEEDAUTH = unmappable? */
		[EIDRM] = LINUX_EIDRM,
		[ENOMSG] = LINUX_ENOMSG,
		[EOVERFLOW] = LINUX_EOVERFLOW,
		[ECANCELED] = LINUX_ECANCELED,
		[EILSEQ] = LINUX_EILSEQ,
		/* EDOOFUS = unmappable? */
		[EBADMSG] = LINUX_EBADMSG,
		[EMULTIHOP] = LINUX_EMULTIHOP,
		[ENOLINK] = LINUX_ENOLINK,
		[EPROTO] = LINUX_EPROTO,
		/* ENOTCAPABLE = unmappable? */
#ifdef ECAPMODE
		[ECAPMODE] = EPERM,
#endif
#ifdef ENOTRECOVERABLE
		[ENOTRECOVERABLE] = LINUX_ENOTRECOVERABLE,
#endif
#ifdef EOWNERDEAD
		[EOWNERDEAD] = LINUX_EOWNERDEAD,
#endif
	};

	/*
	 * In case we want to return a raw Linux errno, allow negative
	 * values a la Linux kernel internals.
	 *
	 * Values up to ERANGE are shared across systems (see
	 * linux_errno.h), except for EAGAIN.
	 */
	if (errnum < 0)
		return (-errnum);

	if ((size_t)errnum < N(table) && table[errnum] != 0)
		return (table[errnum]);

	if (errnum <= ERANGE)
		return (errnum);

	L9P_LOG(L9P_WARNING, "cannot map errno %d to anything reasonable",
	    errnum);

	return (LINUX_ENOTRECOVERABLE);	/* ??? */
}

/*
 * Send response to request, or possibly just drop request.
 * We also need to know whether to remove the request from
 * the tag hash table.
 */
void
l9p_respond(struct l9p_request *req, bool drop, bool rmtag)
{
	struct l9p_connection *conn = req->lr_conn;
	size_t iosize;
#if defined(L9P_DEBUG)
	struct sbuf *sb;
	const char *ftype;
#endif
	int error;

	req->lr_resp.hdr.tag = req->lr_req.hdr.tag;

	error = req->lr_error;
	if (error == 0)
		req->lr_resp.hdr.type = req->lr_req.hdr.type + 1;
	else {
		if (conn->lc_version == L9P_2000L) {
			req->lr_resp.hdr.type = L9P_RLERROR;
			req->lr_resp.error.errnum = (uint32_t)e2linux(error);
		} else {
			req->lr_resp.hdr.type = L9P_RERROR;
			req->lr_resp.error.ename = strerror(error);
			req->lr_resp.error.errnum = (uint32_t)e29p(error);
		}
	}

#if defined(L9P_DEBUG)
	sb = sbuf_new_auto();
	l9p_describe_fcall(&req->lr_resp, conn->lc_version, sb);
	sbuf_finish(sb);

	switch (req->lr_flushstate) {
	case L9P_FLUSH_NONE:
		ftype = "";
		break;
	case L9P_FLUSH_REQUESTED_PRE_START:
		ftype = "FLUSH requested pre-dispatch: ";
		break;
	case L9P_FLUSH_REQUESTED_POST_START:
		ftype = "FLUSH requested while running: ";
		break;
	case L9P_FLUSH_TOOLATE:
		ftype = "FLUSH requested too late: ";
		break;
	}
	L9P_LOG(L9P_DEBUG, "%s%s%s",
	    drop ? "DROP: " : "", ftype, sbuf_data(sb));
	sbuf_delete(sb);
#endif

	error = drop ? 0 :
	    l9p_pufcall(&req->lr_resp_msg, &req->lr_resp, conn->lc_version);
	if (rmtag)
		ht_remove(&conn->lc_requests, req->lr_req.hdr.tag);
	if (error != 0) {
		L9P_LOG(L9P_ERROR, "cannot pack response");
		drop = true;
	}

	if (drop) {
		conn->lc_lt.lt_drop_response(req,
		    req->lr_resp_msg.lm_iov, req->lr_resp_msg.lm_niov,
		    conn->lc_lt.lt_aux);
	} else {
		iosize = req->lr_resp_msg.lm_size;

		/*
		 * Include I/O size in calculation for Rread and
		 * Rreaddir responses.
		 */
		if (req->lr_resp.hdr.type == L9P_RREAD ||
		    req->lr_resp.hdr.type == L9P_RREADDIR)
			iosize += req->lr_resp.io.count;

		conn->lc_lt.lt_send_response(req,
		    req->lr_resp_msg.lm_iov, req->lr_resp_msg.lm_niov,
		    iosize, conn->lc_lt.lt_aux);
	}

	l9p_freefcall(&req->lr_req);
	l9p_freefcall(&req->lr_resp);

	free(req);
}

/*
 * This allows a caller to iterate through the data in a
 * read or write request (creating the data if packing,
 * scanning through it if unpacking).  This is used for
 * writing readdir entries, so mode should be L9P_PACK
 * (but we allow L9P_UNPACK so that debug code can also scan
 * through the data later, if desired).
 *
 * This relies on the Tread op having positioned the request's
 * iov to the beginning of the data buffer (note the l9p_seek_iov
 * in l9p_dispatch_tread).
 */
void
l9p_init_msg(struct l9p_message *msg, struct l9p_request *req,
    enum l9p_pack_mode mode)
{

	msg->lm_size = 0;
	msg->lm_mode = mode;
	msg->lm_cursor_iov = 0;
	msg->lm_cursor_offset = 0;
	msg->lm_niov = req->lr_data_niov;
	memcpy(msg->lm_iov, req->lr_data_iov,
	    sizeof (struct iovec) * req->lr_data_niov);
}

enum fid_lookup_flags {
	F_REQUIRE_OPEN = 0x01,	/* require that the file be marked OPEN */
	F_REQUIRE_DIR = 0x02,	/* require that the file be marked ISDIR */
	F_REQUIRE_XATTR = 0x04,	/* require that the file be marked XATTR */
	F_REQUIRE_AUTH = 0x08,	/* require that the fid be marked AUTH */
	F_FORBID_OPEN = 0x10,	/* forbid that the file be marked OPEN */
	F_FORBID_DIR = 0x20,	/* forbid that the file be marked ISDIR */
	F_FORBID_XATTR = 0x40,	/* forbid that the file be marked XATTR */
	F_ALLOW_AUTH = 0x80,	/* allow that the fid be marked AUTH */
};

/*
 * Look up a fid.  It must correspond to a valid file, else we return
 * the given errno (some "not a valid fid" calls must return EIO and
 * some must return EINVAL and qemu returns ENOENT in other cases and
 * so on, so we just provide a general "return this error number").
 *
 * Callers may also set constraints: fid must be (or not be) open,
 * must be (or not be) a directory, must be (or not be) an xattr.
 *
 * Only one op has a fid that *must* be an auth fid.  Most ops forbid
 * auth fids  So instead of FORBID we have ALLOW here and the default
 * is FORBID.
 */
static inline int
fid_lookup(struct l9p_connection *conn, uint32_t fid, int err, int flags,
    struct l9p_fid **afile)
{
	struct l9p_fid *file;

	file = ht_find(&conn->lc_files, fid);
	if (file == NULL)
		return (err);

	/*
	 * As soon as we go multithreaded / async, this
	 * assert has to become "return EINVAL" or "return err".
	 *
	 * We may also need a way to mark a fid as
	 * "in async op" (valid for some purposes, but cannot be
	 * used elsewhere until async op is completed or aborted).
	 *
	 * For now, this serves for bug-detecting.
	 */
	assert(l9p_fid_isvalid(file));

	/*
	 * Note that we're inline expanded and flags is constant,
	 * so unnecessary tests just drop out entirely.
	 */
	if ((flags & F_REQUIRE_OPEN) && !l9p_fid_isopen(file))
		return (EINVAL);
	if ((flags & F_FORBID_OPEN) && l9p_fid_isopen(file))
		return (EINVAL);
	if ((flags & F_REQUIRE_DIR) && !l9p_fid_isdir(file))
		return (ENOTDIR);
	if ((flags & F_FORBID_DIR) && l9p_fid_isdir(file))
		return (EISDIR);
	if ((flags & F_REQUIRE_XATTR) && !l9p_fid_isxattr(file))
		return (EINVAL);
	if ((flags & F_FORBID_XATTR) && l9p_fid_isxattr(file))
		return (EINVAL);
	if (l9p_fid_isauth(file)) {
		if ((flags & (F_REQUIRE_AUTH | F_ALLOW_AUTH)) == 0)
			return (EINVAL);
	} else if (flags & F_REQUIRE_AUTH)
		return (EINVAL);
	*afile = file;
	return (0);
}

/*
 * Append variable-size stat object and adjust io count.
 * Returns 0 if the entire stat object was packed, -1 if not.
 * A fully packed object updates the request's io count.
 *
 * Caller must use their own private l9p_message object since
 * a partially packed object will leave the message object in
 * a useless state.
 *
 * Frees the stat object.
 */
int
l9p_pack_stat(struct l9p_message *msg, struct l9p_request *req,
    struct l9p_stat *st)
{
	struct l9p_connection *conn = req->lr_conn;
	uint16_t size = l9p_sizeof_stat(st, conn->lc_version);
	int ret = 0;

	assert(msg->lm_mode == L9P_PACK);

	if (req->lr_resp.io.count + size > req->lr_req.io.count ||
	    l9p_pustat(msg, st, conn->lc_version) < 0)
		ret = -1;
	else
		req->lr_resp.io.count += size;
	l9p_freestat(st);
	return (ret);
}

static int
l9p_dispatch_tversion(struct l9p_request *req)
{
	struct l9p_connection *conn = req->lr_conn;
	struct l9p_server *server = conn->lc_server;
	enum l9p_version remote_version = L9P_INVALID_VERSION;
	size_t i;
	const char *remote_version_name;

	for (i = 0; i < N(l9p_versions); i++) {
		if (strcmp(req->lr_req.version.version,
		    l9p_versions[i].name) == 0) {
			remote_version = (enum l9p_version)i;
			break;
		}
	}

	if (remote_version == L9P_INVALID_VERSION) {
		L9P_LOG(L9P_ERROR, "unsupported remote version: %s",
		    req->lr_req.version.version);
		return (ENOSYS);
	}

	remote_version_name = l9p_versions[remote_version].name;
	L9P_LOG(L9P_INFO, "remote version: %s", remote_version_name);
	L9P_LOG(L9P_INFO, "local version: %s",
	    l9p_versions[server->ls_max_version].name);

	conn->lc_version = MIN(remote_version, server->ls_max_version);
	conn->lc_msize = MIN(req->lr_req.version.msize, conn->lc_msize);
	conn->lc_max_io_size = conn->lc_msize - 24;
	req->lr_resp.version.version = strdup(remote_version_name);
	req->lr_resp.version.msize = conn->lc_msize;
	return (0);
}

static int
l9p_dispatch_tattach(struct l9p_request *req)
{
	struct l9p_connection *conn = req->lr_conn;
	struct l9p_backend *be;
	struct l9p_fid *fid;
	int error;

	/*
	 * We still don't have Tauth yet, but let's code this part
	 * anyway.
	 *
	 * Look up the auth fid first since if it fails we can just
	 * return immediately.
	 */
	if (req->lr_req.tattach.afid != L9P_NOFID) {
		error = fid_lookup(conn, req->lr_req.tattach.afid, EINVAL,
		    F_REQUIRE_AUTH, &req->lr_fid2);
		if (error)
			return (error);
	} else
		req->lr_fid2 = NULL;

	fid = l9p_connection_alloc_fid(conn, req->lr_req.hdr.fid);
	if (fid == NULL)
		return (EINVAL);

	be = conn->lc_server->ls_backend;

	req->lr_fid = fid;

	/* For backend convenience, set NONUNAME on 9P2000. */
	if (conn->lc_version == L9P_2000)
		req->lr_req.tattach.n_uname = L9P_NONUNAME;
	error = be->attach(be->softc, req);

	/*
	 * On success, fid becomes valid; on failure, disconnect.
	 * It certainly *should* be a directory here...
	 */
	if (error == 0) {
		l9p_fid_setvalid(fid);
		if (req->lr_resp.rattach.qid.type & L9P_QTDIR)
			l9p_fid_setdir(fid);
	} else
		l9p_connection_remove_fid(conn, fid);
	return (error);
}

static int
l9p_dispatch_tclunk(struct l9p_request *req)
{
	struct l9p_connection *conn = req->lr_conn;
	struct l9p_backend *be;
	struct l9p_fid *fid;
	int error;

	/* Note that clunk is the only way to dispose of an auth fid. */
	error = fid_lookup(conn, req->lr_req.hdr.fid, ENOENT,
	    F_ALLOW_AUTH, &fid);
	if (error)
		return (error);

	be = conn->lc_server->ls_backend;
	l9p_fid_unsetvalid(fid);

	/*
	 * If it's an xattr fid there must, by definition, be an
	 * xattrclunk.  The xattrclunk function can only be NULL if
	 * xattrwalk and xattrcreate are NULL or always return error.
	 *
	 * Q: do we want to allow async xattrclunk in case of very
	 * large xattr create?  This will make things difficult,
	 * so probably not.
	 */
	if (l9p_fid_isxattr(fid))
		error = be->xattrclunk(be->softc, fid);
	else
		error = be->clunk(be->softc, fid);

	/* fid is now gone regardless of any error return */
	l9p_connection_remove_fid(conn, fid);
	return (error);
}

static int
l9p_dispatch_tcreate(struct l9p_request *req)
{
	struct l9p_connection *conn = req->lr_conn;
	struct l9p_backend *be;
	uint32_t dmperm;
	int error;

	/* Incoming fid must represent a directory that has not been opened. */
	error = fid_lookup(conn, req->lr_req.hdr.fid, EINVAL,
	    F_REQUIRE_DIR | F_FORBID_OPEN, &req->lr_fid);
	if (error)
		return (error);

	be = conn->lc_server->ls_backend;
	dmperm = req->lr_req.tcreate.perm;
#define MKDIR_OR_SIMILAR \
    (L9P_DMDIR | L9P_DMSYMLINK | L9P_DMNAMEDPIPE | L9P_DMSOCKET | L9P_DMDEVICE)

	/*
	 * TODO:
	 *  - check new file name
	 *  - break out different kinds of create (file vs mkdir etc)
	 *  - add async file-create (leaves req->lr_fid in limbo)
	 *
	 * A successful file-create changes the fid into an open file.
	 */
	error = be->create(be->softc, req);
	if (error == 0 && (dmperm & MKDIR_OR_SIMILAR) == 0) {
		l9p_fid_unsetdir(req->lr_fid);
		l9p_fid_setopen(req->lr_fid);
	}

	return (error);
}

static int
l9p_dispatch_topen(struct l9p_request *req)
{
	struct l9p_connection *conn = req->lr_conn;
	struct l9p_backend *be;
	int error;

	error = fid_lookup(conn, req->lr_req.hdr.fid, ENOENT,
	    F_FORBID_OPEN | F_FORBID_XATTR, &req->lr_fid);
	if (error)
		return (error);

	be = conn->lc_server->ls_backend;

	/*
	 * TODO:
	 *  - add async open (leaves req->lr_fid in limbo)
	 */
	error = be->open(be->softc, req);
	if (error == 0)
		l9p_fid_setopen(req->lr_fid);
	return (error);
}

static int
l9p_dispatch_tread(struct l9p_request *req)
{
	struct l9p_connection *conn = req->lr_conn;
	struct l9p_backend *be;
	struct l9p_fid *fid;
	int error;

	/* Xattr fids are not open, so we need our own tests. */
	error = fid_lookup(conn, req->lr_req.hdr.fid, EINVAL, 0, &req->lr_fid);
	if (error)
		return (error);

	/*
	 * Adjust so that writing messages (packing data) starts
	 * right after the count field in the response.
	 *
	 * size[4] + Rread[1] + tag[2] + count[4] = 11
	 */
	l9p_seek_iov(req->lr_resp_msg.lm_iov, req->lr_resp_msg.lm_niov,
	    req->lr_data_iov, &req->lr_data_niov, 11);

	/*
	 * If it's an xattr fid there must, by definition, be an
	 * xattrread.  The xattrread function can only be NULL if
	 * xattrwalk and xattrcreate are NULL or always return error.
	 *
	 * TODO:
	 *   separate out directory-read
	 *   allow async read
	 */
	be = conn->lc_server->ls_backend;
	fid = req->lr_fid;
	if (l9p_fid_isxattr(fid)) {
		error = be->xattrread(be->softc, req);
	} else if (l9p_fid_isopen(fid)) {
		error = be->read(be->softc, req);
	} else {
		error = EINVAL;
	}

	return (error);
}

static int
l9p_dispatch_tremove(struct l9p_request *req)
{
	struct l9p_connection *conn = req->lr_conn;
	struct l9p_backend *be;
	struct l9p_fid *fid;
	int error;

	/*
	 * ?? Should we allow Tremove on auth fids? If so, do
	 * we pretend it is just a Tclunk?
	 */
	error = fid_lookup(conn, req->lr_req.hdr.fid, EINVAL, 0, &fid);
	if (error)
		return (error);

	be = conn->lc_server->ls_backend;
	l9p_fid_unsetvalid(fid);

	error = be->remove(be->softc, fid);
	/* fid is now gone regardless of any error return */
	l9p_connection_remove_fid(conn, fid);
	return (error);
}

static int
l9p_dispatch_tstat(struct l9p_request *req)
{
	struct l9p_connection *conn = req->lr_conn;
	struct l9p_backend *be;
	struct l9p_fid *fid;
	int error;

	/* Allow Tstat on auth fid?  Seems harmless enough... */
	error = fid_lookup(conn, req->lr_req.hdr.fid, ENOENT,
	    F_ALLOW_AUTH, &fid);
	if (error)
		return (error);

	be = conn->lc_server->ls_backend;
	req->lr_fid = fid;
	error = be->stat(be->softc, req);

	if (error == 0) {
		if (l9p_fid_isauth(fid))
			req->lr_resp.rstat.stat.qid.type |= L9P_QTAUTH;

		/* should we check req->lr_resp.rstat.qid.type L9P_QTDIR bit? */
		if (req->lr_resp.rstat.stat.qid.type &= L9P_QTDIR)
			l9p_fid_setdir(fid);
		else
			l9p_fid_unsetdir(fid);
	}

	return (error);
}

static int
l9p_dispatch_twalk(struct l9p_request *req)
{
	struct l9p_connection *conn = req->lr_conn;
	struct l9p_backend *be;
	struct l9p_fid *fid, *newfid;
	uint16_t n;
	int error;

	/* Can forbid XATTR, but cannot require DIR. */
	error = fid_lookup(conn, req->lr_req.hdr.fid, ENOENT,
	    F_FORBID_XATTR, &fid);
	if (error)
		return (error);

	if (req->lr_req.twalk.hdr.fid != req->lr_req.twalk.newfid) {
		newfid = l9p_connection_alloc_fid(conn,
		    req->lr_req.twalk.newfid);
		if (newfid == NULL)
			return (EINVAL);
	} else
		newfid = fid;

	be = conn->lc_server->ls_backend;
	req->lr_fid = fid;
	req->lr_newfid = newfid;
	error = be->walk(be->softc, req);

	/*
	 * If newfid == fid, then fid itself has (potentially) changed,
	 * but is still valid.  Otherwise set newfid valid on
	 * success, and destroy it on error.
	 */
	if (newfid != fid) {
		if (error == 0)
			l9p_fid_setvalid(newfid);
		else
			l9p_connection_remove_fid(conn, newfid);
	}

	/*
	 * If we walked any name elements, the last (n-1'th) qid
	 * has the type (dir vs file) for the new fid.  Otherwise
	 * the type of newfid is the same as fid.  Of course, if
	 * n==0 and fid==newfid, fid is already set up correctly
	 * as the whole thing was a big no-op, but it's safe to
	 * copy its dir bit to itself.
	 */
	if (error == 0) {
		n = req->lr_resp.rwalk.nwqid;
		if (n > 0) {
			if (req->lr_resp.rwalk.wqid[n - 1].type & L9P_QTDIR)
				l9p_fid_setdir(newfid);
		} else {
			if (l9p_fid_isdir(fid))
				l9p_fid_setdir(newfid);
		}
	}
	return (error);
}

static int
l9p_dispatch_twrite(struct l9p_request *req)
{
	struct l9p_connection *conn = req->lr_conn;
	struct l9p_backend *be;
	struct l9p_fid *fid;
	int error;

	/* Cannot require open due to xattr write, but can forbid dir. */
	error = fid_lookup(conn, req->lr_req.hdr.fid, EINVAL,
	    F_FORBID_DIR, &req->lr_fid);
	if (error)
		return (error);

	/*
	 * Adjust to point to the data to be written (a la
	 * l9p_dispatch_tread, but we're pointing into the request
	 * buffer rather than the response):
	 *
	 * size[4] + Twrite[1] + tag[2] + fid[4] + offset[8] + count[4] = 23
	 */
	l9p_seek_iov(req->lr_req_msg.lm_iov, req->lr_req_msg.lm_niov,
	    req->lr_data_iov, &req->lr_data_niov, 23);

	/*
	 * Unlike read, write and xattrwrite are optional (for R/O fs).
	 *
	 * TODO:
	 *   allow async write
	 */
	be = conn->lc_server->ls_backend;
	fid = req->lr_fid;
	if (l9p_fid_isxattr(fid)) {
		error = be->xattrwrite != NULL ?
		    be->xattrwrite(be->softc, req) : ENOSYS;
	} else if (l9p_fid_isopen(fid)) {
		error = be->write != NULL ?
		    be->write(be->softc, req) : ENOSYS;
	} else {
		error = EINVAL;
	}

	return (error);
}

static int
l9p_dispatch_twstat(struct l9p_request *req)
{
	struct l9p_connection *conn = req->lr_conn;
	struct l9p_backend *be;
	int error;

	error = fid_lookup(conn, req->lr_req.hdr.fid, EINVAL,
	    F_FORBID_XATTR, &req->lr_fid);
	if (error)
		return (error);

	be = conn->lc_server->ls_backend;
	error = be->wstat != NULL ? be->wstat(be->softc, req) : ENOSYS;
	return (error);
}

static int
l9p_dispatch_tstatfs(struct l9p_request *req)
{
	struct l9p_connection *conn = req->lr_conn;
	struct l9p_backend *be;
	int error;

	/* Should we allow statfs on auth fids? */
	error = fid_lookup(conn, req->lr_req.hdr.fid, EINVAL, 0, &req->lr_fid);
	if (error)
		return (error);

	be = conn->lc_server->ls_backend;
	error = be->statfs(be->softc, req);
	return (error);
}

static int
l9p_dispatch_tlopen(struct l9p_request *req)
{
	struct l9p_connection *conn = req->lr_conn;
	struct l9p_backend *be;
	int error;

	error = fid_lookup(conn, req->lr_req.hdr.fid, ENOENT,
	    F_FORBID_OPEN | F_FORBID_XATTR, &req->lr_fid);
	if (error)
		return (error);

	be = conn->lc_server->ls_backend;

	/*
	 * TODO:
	 *  - add async open (leaves req->lr_fid in limbo)
	 */
	error = be->lopen != NULL ? be->lopen(be->softc, req) : ENOSYS;
	if (error == 0)
		l9p_fid_setopen(req->lr_fid);
	return (error);
}

static int
l9p_dispatch_tlcreate(struct l9p_request *req)
{
	struct l9p_connection *conn = req->lr_conn;
	struct l9p_backend *be;
	int error;

	error = fid_lookup(conn, req->lr_req.hdr.fid, ENOENT,
	    F_REQUIRE_DIR | F_FORBID_OPEN, &req->lr_fid);
	if (error)
		return (error);

	be = conn->lc_server->ls_backend;

	/*
	 * TODO:
	 *  - check new file name
	 *  - add async create (leaves req->lr_fid in limbo)
	 */
	error = be->lcreate != NULL ? be->lcreate(be->softc, req) : ENOSYS;
	if (error == 0) {
		l9p_fid_unsetdir(req->lr_fid);
		l9p_fid_setopen(req->lr_fid);
	}
	return (error);
}

static int
l9p_dispatch_tsymlink(struct l9p_request *req)
{
	struct l9p_connection *conn = req->lr_conn;
	struct l9p_backend *be;
	int error;

	/* This doesn't affect the containing dir; maybe allow OPEN? */
	error = fid_lookup(conn, req->lr_req.hdr.fid, ENOENT,
	    F_REQUIRE_DIR | F_FORBID_OPEN, &req->lr_fid);
	if (error)
		return (error);

	be = conn->lc_server->ls_backend;

	/*
	 * TODO:
	 *  - check new file name
	 */
	error = be->symlink != NULL ? be->symlink(be->softc, req) : ENOSYS;
	return (error);
}

static int
l9p_dispatch_tmknod(struct l9p_request *req)
{
	struct l9p_connection *conn = req->lr_conn;
	struct l9p_backend *be;
	int error;

	/* This doesn't affect the containing dir; maybe allow OPEN? */
	error = fid_lookup(conn, req->lr_req.hdr.fid, ENOENT,
	    F_REQUIRE_DIR | F_FORBID_OPEN, &req->lr_fid);
	if (error)
		return (error);

	be = conn->lc_server->ls_backend;

	/*
	 * TODO:
	 *  - check new file name
	 */
	error = be->mknod != NULL ? be->mknod(be->softc, req) : ENOSYS;
	return (error);
}

static int
l9p_dispatch_trename(struct l9p_request *req)
{
	struct l9p_connection *conn = req->lr_conn;
	struct l9p_backend *be;
	int error;

	/* Rename directory or file (including symlink etc). */
	error = fid_lookup(conn, req->lr_req.hdr.fid, ENOENT,
	    F_FORBID_XATTR, &req->lr_fid);
	if (error)
		return (error);

	/* Doesn't affect new dir fid; maybe allow OPEN? */
	error = fid_lookup(conn, req->lr_req.trename.dfid, ENOENT,
	    F_REQUIRE_DIR | F_FORBID_OPEN, &req->lr_fid2);
	if (error)
		return (error);

	be = conn->lc_server->ls_backend;

	/*
	 * TODO:
	 *  - check new file name (trename.name)
	 */
	error = be->rename != NULL ? be->rename(be->softc, req) : ENOSYS;
	return (error);
}

static int
l9p_dispatch_treadlink(struct l9p_request *req)
{
	struct l9p_connection *conn = req->lr_conn;
	struct l9p_backend *be;
	int error;

	/*
	 * The underlying readlink will fail unless it's a symlink,
	 * and the back end has to check, but we might as well forbid
	 * directories and open files here since it's cheap.
	 */
	error = fid_lookup(conn, req->lr_req.hdr.fid, ENOENT,
	    F_FORBID_DIR | F_FORBID_OPEN, &req->lr_fid);
	if (error)
		return (error);

	be = conn->lc_server->ls_backend;

	error = be->readlink != NULL ? be->readlink(be->softc, req) : ENOSYS;
	return (error);
}

static int
l9p_dispatch_tgetattr(struct l9p_request *req)
{
	struct l9p_connection *conn = req->lr_conn;
	struct l9p_backend *be;
	int error;

	error = fid_lookup(conn, req->lr_req.hdr.fid, ENOENT,
	    F_FORBID_XATTR, &req->lr_fid);
	if (error)
		return (error);

	be = conn->lc_server->ls_backend;

	error = be->getattr != NULL ? be->getattr(be->softc, req) : ENOSYS;
	return (error);
}

static int
l9p_dispatch_tsetattr(struct l9p_request *req)
{
	struct l9p_connection *conn = req->lr_conn;
	struct l9p_backend *be;
	int error;

	error = fid_lookup(conn, req->lr_req.hdr.fid, ENOENT,
	    F_FORBID_XATTR, &req->lr_fid);
	if (error)
		return (error);

	be = conn->lc_server->ls_backend;

	error = be->setattr != NULL ? be->setattr(be->softc, req) : ENOSYS;
	return (error);
}

static int
l9p_dispatch_txattrwalk(struct l9p_request *req)
{
	struct l9p_connection *conn = req->lr_conn;
	struct l9p_backend *be;
	struct l9p_fid *fid, *newfid;
	int error;

	/*
	 * Not sure if we care if file-or-dir is open or not.
	 * However, the fid argument should always be a file or
	 * dir and the newfid argument must be supplied, must
	 * be different, and always becomes a new xattr,
	 * so this is not very much like Twalk.
	 */
	error = fid_lookup(conn, req->lr_req.hdr.fid, ENOENT,
	    F_FORBID_XATTR, &fid);
	if (error)
		return (error);

	newfid = l9p_connection_alloc_fid(conn, req->lr_req.txattrwalk.newfid);
	if (newfid == NULL)
		return (EINVAL);

	be = conn->lc_server->ls_backend;

	req->lr_fid = fid;
	req->lr_newfid = newfid;
	error = be->xattrwalk != NULL ? be->xattrwalk(be->softc, req) : ENOSYS;

	/*
	 * Success/fail is similar to Twalk, except that we need
	 * to set the xattr type bit in the new fid.  It's also
	 * much simpler since newfid is always a new fid.
	 */
	if (error == 0) {
		l9p_fid_setvalid(newfid);
		l9p_fid_setxattr(newfid);
	} else {
		l9p_connection_remove_fid(conn, newfid);
	}
	return (error);
}

static int
l9p_dispatch_txattrcreate(struct l9p_request *req)
{
	struct l9p_connection *conn = req->lr_conn;
	struct l9p_backend *be;
	struct l9p_fid *fid;
	int error;

	/*
	 * Forbid incoming open fid since it's going to become an
	 * xattr fid instead.  If it turns out we need to allow
	 * it, fs code will need to handle this.
	 *
	 * Curiously, qemu 9pfs uses ENOENT for a bad txattrwalk
	 * fid, but EINVAL for txattrcreate (so we do too).
	 */
	error = fid_lookup(conn, req->lr_req.hdr.fid, EINVAL,
	    F_FORBID_XATTR | F_FORBID_OPEN, &fid);
	if (error)
		return (error);

	be = conn->lc_server->ls_backend;

	req->lr_fid = fid;
	error = be->xattrcreate != NULL ? be->xattrcreate(be->softc, req) :
	    ENOSYS;

	/*
	 * On success, fid has changed from a regular (file or dir)
	 * fid to an xattr fid.
	 */
	if (error == 0) {
		l9p_fid_unsetdir(fid);
		l9p_fid_setxattr(fid);
	}
	return (error);
}

static int
l9p_dispatch_treaddir(struct l9p_request *req)
{
	struct l9p_connection *conn = req->lr_conn;
	struct l9p_backend *be;
	int error;

	error = fid_lookup(conn, req->lr_req.hdr.fid, ENOENT,
	    F_REQUIRE_DIR | F_REQUIRE_OPEN, &req->lr_fid);
	if (error)
		return (error);

	/*
	 * Adjust so that writing messages (packing data) starts
	 * right after the count field in the response.
	 *
	 * size[4] + Rreaddir[1] + tag[2] + count[4] = 11
	 */
	l9p_seek_iov(req->lr_resp_msg.lm_iov, req->lr_resp_msg.lm_niov,
	    req->lr_data_iov, &req->lr_data_niov, 11);

	be = conn->lc_server->ls_backend;

	error = be->readdir != NULL ? be->readdir(be->softc, req) : ENOSYS;
	return (error);
}

static int
l9p_dispatch_tfsync(struct l9p_request *req)
{
	struct l9p_connection *conn = req->lr_conn;
	struct l9p_backend *be;
	int error;

	error = fid_lookup(conn, req->lr_req.hdr.fid, ENOENT,
	    F_REQUIRE_OPEN, &req->lr_fid);
	if (error)
		return (error);

	be = conn->lc_server->ls_backend;

	error = be->fsync != NULL ? be->fsync(be->softc, req) : ENOSYS;
	return (error);
}

static int
l9p_dispatch_tlock(struct l9p_request *req)
{
	struct l9p_connection *conn = req->lr_conn;
	struct l9p_backend *be;
	int error;

	/* Forbid directories? */
	error = fid_lookup(conn, req->lr_req.hdr.fid, ENOENT,
	    F_REQUIRE_OPEN, &req->lr_fid);
	if (error)
		return (error);

	be = conn->lc_server->ls_backend;

	/*
	 * TODO: multiple client handling; perhaps async locking.
	 */
	error = be->lock != NULL ? be->lock(be->softc, req) : ENOSYS;
	return (error);
}

static int
l9p_dispatch_tgetlock(struct l9p_request *req)
{
	struct l9p_connection *conn = req->lr_conn;
	struct l9p_backend *be;
	int error;

	error = fid_lookup(conn, req->lr_req.hdr.fid, ENOENT,
	    F_REQUIRE_OPEN, &req->lr_fid);
	if (error)
		return (error);

	be = conn->lc_server->ls_backend;

	/*
	 * TODO: multiple client handling; perhaps async locking.
	 */
	error = be->getlock != NULL ? be->getlock(be->softc, req) : ENOSYS;
	return (error);
}

static int
l9p_dispatch_tlink(struct l9p_request *req)
{
	struct l9p_connection *conn = req->lr_conn;
	struct l9p_backend *be;
	int error;

	/*
	 * Note, dfid goes into fid2 in current scheme.
	 *
	 * Allow open dir?  Target dir fid is not modified...
	 */
	error = fid_lookup(conn, req->lr_req.tlink.dfid, ENOENT,
	    F_REQUIRE_DIR | F_FORBID_OPEN, &req->lr_fid2);
	if (error)
		return (error);

	error = fid_lookup(conn, req->lr_req.hdr.fid, ENOENT,
	    F_FORBID_DIR | F_FORBID_XATTR, &req->lr_fid);
	if (error)
		return (error);

	be = conn->lc_server->ls_backend;

	error = be->link != NULL ? be->link(be->softc, req) : ENOSYS;
	return (error);
}

static int
l9p_dispatch_tmkdir(struct l9p_request *req)
{
	struct l9p_connection *conn = req->lr_conn;
	struct l9p_backend *be;
	int error;

	error = fid_lookup(conn, req->lr_req.hdr.fid, ENOENT,
	    F_REQUIRE_DIR | F_FORBID_OPEN, &req->lr_fid);
	if (error)
		return (error);

	/* Slashes embedded in the name are not allowed */
	if (strchr(req->lr_req.tlcreate.name, '/') != NULL)
		return (EINVAL);

	be = conn->lc_server->ls_backend;
	error = be->mkdir != NULL ? be->mkdir(be->softc, req) : ENOSYS;
	return (error);
}

static int
l9p_dispatch_trenameat(struct l9p_request *req)
{
	struct l9p_connection *conn = req->lr_conn;
	struct l9p_backend *be;
	int error;

	error = fid_lookup(conn, req->lr_req.hdr.fid, ENOENT,
	    F_REQUIRE_DIR | F_FORBID_OPEN, &req->lr_fid);
	if (error)
		return (error);

	error = fid_lookup(conn, req->lr_req.trenameat.newdirfid, ENOENT,
	    F_REQUIRE_DIR | F_FORBID_OPEN, &req->lr_fid2);
	if (error)
		return (error);

	be = conn->lc_server->ls_backend;

	/* TODO: check old and new names */
	error = be->renameat != NULL ? be->renameat(be->softc, req) : ENOSYS;
	return (error);
}

static int
l9p_dispatch_tunlinkat(struct l9p_request *req)
{
	struct l9p_connection *conn = req->lr_conn;
	struct l9p_backend *be;
	int error;

	error = fid_lookup(conn, req->lr_req.hdr.fid, ENOENT,
	    F_REQUIRE_DIR | F_FORBID_OPEN, &req->lr_fid);
	if (error)
		return (error);

	be = conn->lc_server->ls_backend;

	/* TODO: check dir-or-file name */
	error = be->unlinkat != NULL ? be->unlinkat(be->softc, req) : ENOSYS;
	return (error);
}