/*
 * fs/nfs/idmap.c
 *
 *  UID and GID to name mapping for clients.
 *
 *  Copyright (c) 2002 The Regents of the University of Michigan.
 *  All rights reserved.
 *
 *  Marius Aamodt Eriksen <marius@umich.edu>
 *
 *  Redistribution and use in source and binary forms, with or without
 *  modification, are permitted provided that the following conditions
 *  are met:
 *
 *  1. Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *  2. Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *  3. Neither the name of the University nor the names of its
 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 *  THIS SOFTWARE IS PROVIDED ``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 REGENTS 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 <linux/types.h>
#include <linux/parser.h>
#include <linux/fs.h>
#include <linux/nfs_idmap.h>
#include <net/net_namespace.h>
#include <linux/sunrpc/rpc_pipe_fs.h>
#include <linux/nfs_fs.h>
#include <linux/nfs_fs_sb.h>
#include <linux/key.h>
#include <linux/keyctl.h>
#include <linux/key-type.h>
#include <keys/user-type.h>
#include <linux/module.h>

#include "internal.h"
#include "netns.h"

#define NFS_UINT_MAXLEN 11

/* Default cache timeout is 10 minutes */
unsigned int nfs_idmap_cache_timeout = 600;
static const struct cred *id_resolver_cache;
static struct key_type key_type_id_resolver_legacy;


/**
 * nfs_fattr_init_names - initialise the nfs_fattr owner_name/group_name fields
 * @fattr: fully initialised struct nfs_fattr
 * @owner_name: owner name string cache
 * @group_name: group name string cache
 */
void nfs_fattr_init_names(struct nfs_fattr *fattr,
                struct nfs4_string *owner_name,
                struct nfs4_string *group_name)
{
        fattr->owner_name = owner_name;
        fattr->group_name = group_name;
}

static void nfs_fattr_free_owner_name(struct nfs_fattr *fattr)
{
        fattr->valid &= ~NFS_ATTR_FATTR_OWNER_NAME;
        kfree(fattr->owner_name->data);
}

static void nfs_fattr_free_group_name(struct nfs_fattr *fattr)
{
        fattr->valid &= ~NFS_ATTR_FATTR_GROUP_NAME;
        kfree(fattr->group_name->data);
}

static bool nfs_fattr_map_owner_name(struct nfs_server *server, struct nfs_fattr *fattr)
{
        struct nfs4_string *owner = fattr->owner_name;
        __u32 uid;

        if (!(fattr->valid & NFS_ATTR_FATTR_OWNER_NAME))
                return false;
        if (nfs_map_name_to_uid(server, owner->data, owner->len, &uid) == 0) {
                fattr->uid = uid;
                fattr->valid |= NFS_ATTR_FATTR_OWNER;
        }
        return true;
}

static bool nfs_fattr_map_group_name(struct nfs_server *server, struct nfs_fattr *fattr)
{
        struct nfs4_string *group = fattr->group_name;
        __u32 gid;

        if (!(fattr->valid & NFS_ATTR_FATTR_GROUP_NAME))
                return false;
        if (nfs_map_group_to_gid(server, group->data, group->len, &gid) == 0) {
                fattr->gid = gid;
                fattr->valid |= NFS_ATTR_FATTR_GROUP;
        }
        return true;
}

/**
 * nfs_fattr_free_names - free up the NFSv4 owner and group strings
 * @fattr: a fully initialised nfs_fattr structure
 */
void nfs_fattr_free_names(struct nfs_fattr *fattr)
{
        if (fattr->valid & NFS_ATTR_FATTR_OWNER_NAME)
                nfs_fattr_free_owner_name(fattr);
        if (fattr->valid & NFS_ATTR_FATTR_GROUP_NAME)
                nfs_fattr_free_group_name(fattr);
}

/**
 * nfs_fattr_map_and_free_names - map owner/group strings into uid/gid and free
 * @server: pointer to the filesystem nfs_server structure
 * @fattr: a fully initialised nfs_fattr structure
 *
 * This helper maps the cached NFSv4 owner/group strings in fattr into
 * their numeric uid/gid equivalents, and then frees the cached strings.
 */
void nfs_fattr_map_and_free_names(struct nfs_server *server, struct nfs_fattr *fattr)
{
        if (nfs_fattr_map_owner_name(server, fattr))
                nfs_fattr_free_owner_name(fattr);
        if (nfs_fattr_map_group_name(server, fattr))
                nfs_fattr_free_group_name(fattr);
}

static int nfs_map_string_to_numeric(const char *name, size_t namelen, __u32 *res)
{
        unsigned long val;
        char buf[16];

        if (memchr(name, '@', namelen) != NULL || namelen >= sizeof(buf))
                return 0;
        memcpy(buf, name, namelen);
        buf[namelen] = '\0';
        if (strict_strtoul(buf, 0, &val) != 0)
                return 0;
        *res = val;
        return 1;
}

static int nfs_map_numeric_to_string(__u32 id, char *buf, size_t buflen)
{
        return snprintf(buf, buflen, "%u", id);
}

static struct key_type key_type_id_resolver = {
        .name           = "id_resolver",
        .instantiate    = user_instantiate,
        .match          = user_match,
        .revoke         = user_revoke,
        .destroy        = user_destroy,
        .describe       = user_describe,
        .read           = user_read,
};

static int nfs_idmap_init_keyring(void)
{
        struct cred *cred;
        struct key *keyring;
        int ret = 0;

        printk(KERN_NOTICE "NFS: Registering the %s key type\n",
                key_type_id_resolver.name);

        cred = prepare_kernel_cred(NULL);
        if (!cred)
                return -ENOMEM;

        keyring = key_alloc(&key_type_keyring, ".id_resolver", 0, 0, cred,
                             (KEY_POS_ALL & ~KEY_POS_SETATTR) |
                             KEY_USR_VIEW | KEY_USR_READ,
                             KEY_ALLOC_NOT_IN_QUOTA);
        if (IS_ERR(keyring)) {
                ret = PTR_ERR(keyring);
                goto failed_put_cred;
        }

        ret = key_instantiate_and_link(keyring, NULL, 0, NULL, NULL);
        if (ret < 0)
                goto failed_put_key;

        ret = register_key_type(&key_type_id_resolver);
        if (ret < 0)
                goto failed_put_key;

        set_bit(KEY_FLAG_ROOT_CAN_CLEAR, &keyring->flags);
        cred->thread_keyring = keyring;
        cred->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
        id_resolver_cache = cred;
        return 0;

failed_put_key:
        key_put(keyring);
failed_put_cred:
        put_cred(cred);
        return ret;
}

static void nfs_idmap_quit_keyring(void)
{
        key_revoke(id_resolver_cache->thread_keyring);
        unregister_key_type(&key_type_id_resolver);
        put_cred(id_resolver_cache);
}

/*
 * Assemble the description to pass to request_key()
 * This function will allocate a new string and update dest to point
 * at it.  The caller is responsible for freeing dest.
 *
 * On error 0 is returned.  Otherwise, the length of dest is returned.
 */
static ssize_t nfs_idmap_get_desc(const char *name, size_t namelen,
                                const char *type, size_t typelen, char **desc)
{
        char *cp;
        size_t desclen = typelen + namelen + 2;

        *desc = kmalloc(desclen, GFP_KERNEL);
        if (!*desc)
                return -ENOMEM;

        cp = *desc;
        memcpy(cp, type, typelen);
        cp += typelen;
        *cp++ = ':';

        memcpy(cp, name, namelen);
        cp += namelen;
        *cp = '\0';
        return desclen;
}

static ssize_t nfs_idmap_request_key(struct key_type *key_type,
                                     const char *name, size_t namelen,
                                     const char *type, void *data,
                                     size_t data_size, struct idmap *idmap)
{
        const struct cred *saved_cred;
        struct key *rkey;
        char *desc;
        struct user_key_payload *payload;
        ssize_t ret;

        ret = nfs_idmap_get_desc(name, namelen, type, strlen(type), &desc);
        if (ret <= 0)
                goto out;

        saved_cred = override_creds(id_resolver_cache);
        if (idmap)
                rkey = request_key_with_auxdata(key_type, desc, "", 0, idmap);
        else
                rkey = request_key(&key_type_id_resolver, desc, "");
        revert_creds(saved_cred);

        kfree(desc);
        if (IS_ERR(rkey)) {
                ret = PTR_ERR(rkey);
                goto out;
        }

        rcu_read_lock();
        rkey->perm |= KEY_USR_VIEW;

        ret = key_validate(rkey);
        if (ret < 0)
                goto out_up;

        payload = rcu_dereference(rkey->payload.data);
        if (IS_ERR_OR_NULL(payload)) {
                ret = PTR_ERR(payload);
                goto out_up;
        }

        ret = payload->datalen;
        if (ret > 0 && ret <= data_size)
                memcpy(data, payload->data, ret);
        else
                ret = -EINVAL;

out_up:
        rcu_read_unlock();
        key_put(rkey);
out:
        return ret;
}

static ssize_t nfs_idmap_get_key(const char *name, size_t namelen,
                                 const char *type, void *data,
                                 size_t data_size, struct idmap *idmap)
{
        ssize_t ret = nfs_idmap_request_key(&key_type_id_resolver,
                                            name, namelen, type, data,
                                            data_size, NULL);
        if (ret < 0) {
                ret = nfs_idmap_request_key(&key_type_id_resolver_legacy,
                                            name, namelen, type, data,
                                            data_size, idmap);
        }
        return ret;
}

/* ID -> Name */
static ssize_t nfs_idmap_lookup_name(__u32 id, const char *type, char *buf,
                                     size_t buflen, struct idmap *idmap)
{
        char id_str[NFS_UINT_MAXLEN];
        int id_len;
        ssize_t ret;

        id_len = snprintf(id_str, sizeof(id_str), "%u", id);
        ret = nfs_idmap_get_key(id_str, id_len, type, buf, buflen, idmap);
        if (ret < 0)
                return -EINVAL;
        return ret;
}

/* Name -> ID */
static int nfs_idmap_lookup_id(const char *name, size_t namelen, const char *type,
                               __u32 *id, struct idmap *idmap)
{
        char id_str[NFS_UINT_MAXLEN];
        long id_long;
        ssize_t data_size;
        int ret = 0;

        data_size = nfs_idmap_get_key(name, namelen, type, id_str, NFS_UINT_MAXLEN, idmap);
        if (data_size <= 0) {
                ret = -EINVAL;
        } else {
                ret = strict_strtol(id_str, 10, &id_long);
                *id = (__u32)id_long;
        }
        return ret;
}

/* idmap classic begins here */
module_param(nfs_idmap_cache_timeout, int, 0644);

struct idmap {
        struct rpc_pipe         *idmap_pipe;
        struct key_construction *idmap_key_cons;
};

enum {
        Opt_find_uid, Opt_find_gid, Opt_find_user, Opt_find_group, Opt_find_err
};

static const match_table_t nfs_idmap_tokens = {
        { Opt_find_uid, "uid:%s" },
        { Opt_find_gid, "gid:%s" },
        { Opt_find_user, "user:%s" },
        { Opt_find_group, "group:%s" },
        { Opt_find_err, NULL }
};

static int nfs_idmap_legacy_upcall(struct key_construction *, const char *, void *);
static ssize_t idmap_pipe_downcall(struct file *, const char __user *,
                                   size_t);
static void idmap_pipe_destroy_msg(struct rpc_pipe_msg *);

static const struct rpc_pipe_ops idmap_upcall_ops = {
        .upcall         = rpc_pipe_generic_upcall,
        .downcall       = idmap_pipe_downcall,
        .destroy_msg    = idmap_pipe_destroy_msg,
};

static struct key_type key_type_id_resolver_legacy = {
        .name           = "id_resolver",
        .instantiate    = user_instantiate,
        .match          = user_match,
        .revoke         = user_revoke,
        .destroy        = user_destroy,
        .describe       = user_describe,
        .read           = user_read,
        .request_key    = nfs_idmap_legacy_upcall,
};

static void __nfs_idmap_unregister(struct rpc_pipe *pipe)
{
        if (pipe->dentry)
                rpc_unlink(pipe->dentry);
}

static int __nfs_idmap_register(struct dentry *dir,
                                     struct idmap *idmap,
                                     struct rpc_pipe *pipe)
{
        struct dentry *dentry;

        dentry = rpc_mkpipe_dentry(dir, "idmap", idmap, pipe);
        if (IS_ERR(dentry))
                return PTR_ERR(dentry);
        pipe->dentry = dentry;
        return 0;
}

static void nfs_idmap_unregister(struct nfs_client *clp,
                                      struct rpc_pipe *pipe)
{
        struct net *net = clp->net;
        struct super_block *pipefs_sb;

        pipefs_sb = rpc_get_sb_net(net);
        if (pipefs_sb) {
                __nfs_idmap_unregister(pipe);
                rpc_put_sb_net(net);
        }
}

static int nfs_idmap_register(struct nfs_client *clp,
                                   struct idmap *idmap,
                                   struct rpc_pipe *pipe)
{
        struct net *net = clp->net;
        struct super_block *pipefs_sb;
        int err = 0;

        pipefs_sb = rpc_get_sb_net(net);
        if (pipefs_sb) {
                if (clp->cl_rpcclient->cl_dentry)
                        err = __nfs_idmap_register(clp->cl_rpcclient->cl_dentry,
                                                   idmap, pipe);
                rpc_put_sb_net(net);
        }
        return err;
}

int
nfs_idmap_new(struct nfs_client *clp)
{
        struct idmap *idmap;
        struct rpc_pipe *pipe;
        int error;

        BUG_ON(clp->cl_idmap != NULL);

        idmap = kzalloc(sizeof(*idmap), GFP_KERNEL);
        if (idmap == NULL)
                return -ENOMEM;

        pipe = rpc_mkpipe_data(&idmap_upcall_ops, 0);
        if (IS_ERR(pipe)) {
                error = PTR_ERR(pipe);
                kfree(idmap);
                return error;
        }
        error = nfs_idmap_register(clp, idmap, pipe);
        if (error) {
                rpc_destroy_pipe_data(pipe);
                kfree(idmap);
                return error;
        }
        idmap->idmap_pipe = pipe;

        clp->cl_idmap = idmap;
        return 0;
}

void
nfs_idmap_delete(struct nfs_client *clp)
{
        struct idmap *idmap = clp->cl_idmap;

        if (!idmap)
                return;
        nfs_idmap_unregister(clp, idmap->idmap_pipe);
        rpc_destroy_pipe_data(idmap->idmap_pipe);
        clp->cl_idmap = NULL;
        kfree(idmap);
}

static int __rpc_pipefs_event(struct nfs_client *clp, unsigned long event,
                              struct super_block *sb)
{
        int err = 0;

        switch (event) {
        case RPC_PIPEFS_MOUNT:
                BUG_ON(clp->cl_rpcclient->cl_dentry == NULL);
                err = __nfs_idmap_register(clp->cl_rpcclient->cl_dentry,
                                                clp->cl_idmap,
                                                clp->cl_idmap->idmap_pipe);
                break;
        case RPC_PIPEFS_UMOUNT:
                if (clp->cl_idmap->idmap_pipe) {
                        struct dentry *parent;

                        parent = clp->cl_idmap->idmap_pipe->dentry->d_parent;
                        __nfs_idmap_unregister(clp->cl_idmap->idmap_pipe);
                        /*
                         * Note: This is a dirty hack. SUNRPC hook has been
                         * called already but simple_rmdir() call for the
                         * directory returned with error because of idmap pipe
                         * inside. Thus now we have to remove this directory
                         * here.
                         */
                        if (rpc_rmdir(parent))
                                printk(KERN_ERR "NFS: %s: failed to remove "
                                        "clnt dir!\n", __func__);
                }
                break;
        default:
                printk(KERN_ERR "NFS: %s: unknown event: %ld\n", __func__,
                        event);
                return -ENOTSUPP;
        }
        return err;
}

static struct nfs_client *nfs_get_client_for_event(struct net *net, int event)
{
        struct nfs_net *nn = net_generic(net, nfs_net_id);
        struct dentry *cl_dentry;
        struct nfs_client *clp;

        spin_lock(&nn->nfs_client_lock);
        list_for_each_entry(clp, &nn->nfs_client_list, cl_share_link) {
                if (clp->rpc_ops != &nfs_v4_clientops)
                        continue;
                cl_dentry = clp->cl_idmap->idmap_pipe->dentry;
                if (((event == RPC_PIPEFS_MOUNT) && cl_dentry) ||
                    ((event == RPC_PIPEFS_UMOUNT) && !cl_dentry))
                        continue;
                atomic_inc(&clp->cl_count);
                spin_unlock(&nn->nfs_client_lock);
                return clp;
        }
        spin_unlock(&nn->nfs_client_lock);
        return NULL;
}

static int rpc_pipefs_event(struct notifier_block *nb, unsigned long event,
                            void *ptr)
{
        struct super_block *sb = ptr;
        struct nfs_client *clp;
        int error = 0;

        if (!try_module_get(THIS_MODULE))
                return 0;

        while ((clp = nfs_get_client_for_event(sb->s_fs_info, event))) {
                error = __rpc_pipefs_event(clp, event, sb);
                nfs_put_client(clp);
                if (error)
                        break;
        }
        module_put(THIS_MODULE);
        return error;
}

#define PIPEFS_NFS_PRIO         1

static struct notifier_block nfs_idmap_block = {
        .notifier_call  = rpc_pipefs_event,
        .priority       = SUNRPC_PIPEFS_NFS_PRIO,
};

int nfs_idmap_init(void)
{
        int ret;
        ret = nfs_idmap_init_keyring();
        if (ret != 0)
                goto out;
        ret = rpc_pipefs_notifier_register(&nfs_idmap_block);
        if (ret != 0)
                nfs_idmap_quit_keyring();
out:
        return ret;
}

void nfs_idmap_quit(void)
{
        rpc_pipefs_notifier_unregister(&nfs_idmap_block);
        nfs_idmap_quit_keyring();
}

static int nfs_idmap_prepare_message(char *desc, struct idmap_msg *im,
                                     struct rpc_pipe_msg *msg)
{
        substring_t substr;
        int token, ret;

        memset(im,  0, sizeof(*im));
        memset(msg, 0, sizeof(*msg));

        im->im_type = IDMAP_TYPE_GROUP;
        token = match_token(desc, nfs_idmap_tokens, &substr);

        switch (token) {
        case Opt_find_uid:
                im->im_type = IDMAP_TYPE_USER;
        case Opt_find_gid:
                im->im_conv = IDMAP_CONV_NAMETOID;
                ret = match_strlcpy(im->im_name, &substr, IDMAP_NAMESZ);
                break;

        case Opt_find_user:
                im->im_type = IDMAP_TYPE_USER;
        case Opt_find_group:
                im->im_conv = IDMAP_CONV_IDTONAME;
                ret = match_int(&substr, &im->im_id);
                break;

        default:
                ret = -EINVAL;
                goto out;
        }

        msg->data = im;
        msg->len  = sizeof(struct idmap_msg);

out:
        return ret;
}

static int nfs_idmap_legacy_upcall(struct key_construction *cons,
                                   const char *op,
                                   void *aux)
{
        struct rpc_pipe_msg *msg;
        struct idmap_msg *im;
        struct idmap *idmap = (struct idmap *)aux;
        struct key *key = cons->key;
        int ret;

        /* msg and im are freed in idmap_pipe_destroy_msg */
        msg = kmalloc(sizeof(*msg), GFP_KERNEL);
        if (IS_ERR(msg)) {
                ret = PTR_ERR(msg);
                goto out0;
        }

        im = kmalloc(sizeof(*im), GFP_KERNEL);
        if (IS_ERR(im)) {
                ret = PTR_ERR(im);
                goto out1;
        }

        ret = nfs_idmap_prepare_message(key->description, im, msg);
        if (ret < 0)
                goto out2;

        idmap->idmap_key_cons = cons;

        ret = rpc_queue_upcall(idmap->idmap_pipe, msg);
        if (ret < 0)
                goto out2;

        return ret;

out2:
        kfree(im);
out1:
        kfree(msg);
out0:
        key_revoke(cons->key);
        key_revoke(cons->authkey);
        return ret;
}

static int nfs_idmap_instantiate(struct key *key, struct key *authkey, char *data)
{
        return key_instantiate_and_link(key, data, strlen(data) + 1,
                                        id_resolver_cache->thread_keyring,
                                        authkey);
}

static int nfs_idmap_read_message(struct idmap_msg *im, struct key *key, struct key *authkey)
{
        char id_str[NFS_UINT_MAXLEN];
        int ret = -EINVAL;

        switch (im->im_conv) {
        case IDMAP_CONV_NAMETOID:
                sprintf(id_str, "%d", im->im_id);
                ret = nfs_idmap_instantiate(key, authkey, id_str);
                break;
        case IDMAP_CONV_IDTONAME:
                ret = nfs_idmap_instantiate(key, authkey, im->im_name);
                break;
        }

        return ret;
}

static ssize_t
idmap_pipe_downcall(struct file *filp, const char __user *src, size_t mlen)
{
        struct rpc_inode *rpci = RPC_I(filp->f_path.dentry->d_inode);
        struct idmap *idmap = (struct idmap *)rpci->private;
        struct key_construction *cons = idmap->idmap_key_cons;
        struct idmap_msg im;
        size_t namelen_in;
        int ret;

        if (mlen != sizeof(im)) {
                ret = -ENOSPC;
                goto out;
        }

        if (copy_from_user(&im, src, mlen) != 0) {
                ret = -EFAULT;
                goto out;
        }

        if (!(im.im_status & IDMAP_STATUS_SUCCESS)) {
                ret = mlen;
                complete_request_key(idmap->idmap_key_cons, -ENOKEY);
                goto out_incomplete;
        }

        namelen_in = strnlen(im.im_name, IDMAP_NAMESZ);
        if (namelen_in == 0 || namelen_in == IDMAP_NAMESZ) {
                ret = -EINVAL;
                goto out;
        }

        ret = nfs_idmap_read_message(&im, cons->key, cons->authkey);
        if (ret >= 0) {
                key_set_timeout(cons->key, nfs_idmap_cache_timeout);
                ret = mlen;
        }

out:
        complete_request_key(idmap->idmap_key_cons, ret);
out_incomplete:
        return ret;
}

static void
idmap_pipe_destroy_msg(struct rpc_pipe_msg *msg)
{
        /* Free memory allocated in nfs_idmap_legacy_upcall() */
        kfree(msg->data);
        kfree(msg);
}

int nfs_map_name_to_uid(const struct nfs_server *server, const char *name, size_t namelen, __u32 *uid)
{
        struct idmap *idmap = server->nfs_client->cl_idmap;

        if (nfs_map_string_to_numeric(name, namelen, uid))
                return 0;
        return nfs_idmap_lookup_id(name, namelen, "uid", uid, idmap);
}

int nfs_map_group_to_gid(const struct nfs_server *server, const char *name, size_t namelen, __u32 *gid)
{
        struct idmap *idmap = server->nfs_client->cl_idmap;

        if (nfs_map_string_to_numeric(name, namelen, gid))
                return 0;
        return nfs_idmap_lookup_id(name, namelen, "gid", gid, idmap);
}

int nfs_map_uid_to_name(const struct nfs_server *server, __u32 uid, char *buf, size_t buflen)
{
        struct idmap *idmap = server->nfs_client->cl_idmap;
        int ret = -EINVAL;

        if (!(server->caps & NFS_CAP_UIDGID_NOMAP))
                ret = nfs_idmap_lookup_name(uid, "user", buf, buflen, idmap);
        if (ret < 0)
                ret = nfs_map_numeric_to_string(uid, buf, buflen);
        return ret;
}
int nfs_map_gid_to_group(const struct nfs_server *server, __u32 gid, char *buf, size_t buflen)
{
        struct idmap *idmap = server->nfs_client->cl_idmap;
        int ret = -EINVAL;

        if (!(server->caps & NFS_CAP_UIDGID_NOMAP))
                ret = nfs_idmap_lookup_name(gid, "group", buf, buflen, idmap);
        if (ret < 0)
                ret = nfs_map_numeric_to_string(gid, buf, buflen);
        return ret;
}