/*
 * 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>
#ifdef __illumos__
#include <sys/sysmacros.h>
#endif
#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,
#ifndef __illumos__
                [EPROCLIM] = LINUX_EAGAIN,
#endif
                [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:
        default:
                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, &req->lr_fid);
        if (error)
                return (error);

        error = fid_lookup(conn, req->lr_req.trenameat.newdirfid, ENOENT,
            F_REQUIRE_DIR, &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, &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);
}