// SPDX-License-Identifier: GPL-2.0-only
/*
 *  linux/fs/9p/vfs_inode.c
 *
 * This file contains vfs inode ops for the 9P2000 protocol.
 *
 *  Copyright (C) 2004 by Eric Van Hensbergen <ericvh@gmail.com>
 *  Copyright (C) 2002 by Ron Minnich <rminnich@lanl.gov>
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/errno.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/pagemap.h>
#include <linux/stat.h>
#include <linux/string.h>
#include <linux/inet.h>
#include <linux/namei.h>
#include <linux/idr.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/xattr.h>
#include <linux/posix_acl.h>
#include <net/9p/9p.h>
#include <net/9p/client.h>

#include "v9fs.h"
#include "v9fs_vfs.h"
#include "fid.h"
#include "cache.h"
#include "xattr.h"
#include "acl.h"

static const struct inode_operations v9fs_dir_inode_operations;
static const struct inode_operations v9fs_dir_inode_operations_dotu;
static const struct inode_operations v9fs_file_inode_operations;
static const struct inode_operations v9fs_symlink_inode_operations;

/**
 * unixmode2p9mode - convert unix mode bits to plan 9
 * @v9ses: v9fs session information
 * @mode: mode to convert
 *
 */

static u32 unixmode2p9mode(struct v9fs_session_info *v9ses, umode_t mode)
{
        int res;
        res = mode & 0777;
        if (S_ISDIR(mode))
                res |= P9_DMDIR;
        if (v9fs_proto_dotu(v9ses)) {
                if (v9ses->nodev == 0) {
                        if (S_ISSOCK(mode))
                                res |= P9_DMSOCKET;
                        if (S_ISFIFO(mode))
                                res |= P9_DMNAMEDPIPE;
                        if (S_ISBLK(mode))
                                res |= P9_DMDEVICE;
                        if (S_ISCHR(mode))
                                res |= P9_DMDEVICE;
                }

                if ((mode & S_ISUID) == S_ISUID)
                        res |= P9_DMSETUID;
                if ((mode & S_ISGID) == S_ISGID)
                        res |= P9_DMSETGID;
                if ((mode & S_ISVTX) == S_ISVTX)
                        res |= P9_DMSETVTX;
        }
        return res;
}

/**
 * p9mode2perm- convert plan9 mode bits to unix permission bits
 * @v9ses: v9fs session information
 * @stat: p9_wstat from which mode need to be derived
 *
 */
static int p9mode2perm(struct v9fs_session_info *v9ses,
                       struct p9_wstat *stat)
{
        int res;
        int mode = stat->mode;

        res = mode & S_IALLUGO;
        if (v9fs_proto_dotu(v9ses)) {
                if ((mode & P9_DMSETUID) == P9_DMSETUID)
                        res |= S_ISUID;

                if ((mode & P9_DMSETGID) == P9_DMSETGID)
                        res |= S_ISGID;

                if ((mode & P9_DMSETVTX) == P9_DMSETVTX)
                        res |= S_ISVTX;
        }
        return res;
}

/**
 * p9mode2unixmode- convert plan9 mode bits to unix mode bits
 * @v9ses: v9fs session information
 * @stat: p9_wstat from which mode need to be derived
 * @rdev: major number, minor number in case of device files.
 *
 */
static umode_t p9mode2unixmode(struct v9fs_session_info *v9ses,
                               struct p9_wstat *stat, dev_t *rdev)
{
        int res;
        u32 mode = stat->mode;

        *rdev = 0;
        res = p9mode2perm(v9ses, stat);

        if ((mode & P9_DMDIR) == P9_DMDIR)
                res |= S_IFDIR;
        else if ((mode & P9_DMSYMLINK) && (v9fs_proto_dotu(v9ses)))
                res |= S_IFLNK;
        else if ((mode & P9_DMSOCKET) && (v9fs_proto_dotu(v9ses))
                 && (v9ses->nodev == 0))
                res |= S_IFSOCK;
        else if ((mode & P9_DMNAMEDPIPE) && (v9fs_proto_dotu(v9ses))
                 && (v9ses->nodev == 0))
                res |= S_IFIFO;
        else if ((mode & P9_DMDEVICE) && (v9fs_proto_dotu(v9ses))
                 && (v9ses->nodev == 0)) {
                char type = 0, ext[32];
                int major = -1, minor = -1;

                strlcpy(ext, stat->extension, sizeof(ext));
                sscanf(ext, "%c %i %i", &type, &major, &minor);
                switch (type) {
                case 'c':
                        res |= S_IFCHR;
                        break;
                case 'b':
                        res |= S_IFBLK;
                        break;
                default:
                        p9_debug(P9_DEBUG_ERROR, "Unknown special type %c %s\n",
                                 type, stat->extension);
                };
                *rdev = MKDEV(major, minor);
        } else
                res |= S_IFREG;

        return res;
}

/**
 * v9fs_uflags2omode- convert posix open flags to plan 9 mode bits
 * @uflags: flags to convert
 * @extended: if .u extensions are active
 */

int v9fs_uflags2omode(int uflags, int extended)
{
        int ret;

        ret = 0;
        switch (uflags&3) {
        default:
        case O_RDONLY:
                ret = P9_OREAD;
                break;

        case O_WRONLY:
                ret = P9_OWRITE;
                break;

        case O_RDWR:
                ret = P9_ORDWR;
                break;
        }

        if (extended) {
                if (uflags & O_EXCL)
                        ret |= P9_OEXCL;

                if (uflags & O_APPEND)
                        ret |= P9_OAPPEND;
        }

        return ret;
}

/**
 * v9fs_blank_wstat - helper function to setup a 9P stat structure
 * @wstat: structure to initialize
 *
 */

void
v9fs_blank_wstat(struct p9_wstat *wstat)
{
        wstat->type = ~0;
        wstat->dev = ~0;
        wstat->qid.type = ~0;
        wstat->qid.version = ~0;
        *((long long *)&wstat->qid.path) = ~0;
        wstat->mode = ~0;
        wstat->atime = ~0;
        wstat->mtime = ~0;
        wstat->length = ~0;
        wstat->name = NULL;
        wstat->uid = NULL;
        wstat->gid = NULL;
        wstat->muid = NULL;
        wstat->n_uid = INVALID_UID;
        wstat->n_gid = INVALID_GID;
        wstat->n_muid = INVALID_UID;
        wstat->extension = NULL;
}

/**
 * v9fs_alloc_inode - helper function to allocate an inode
 *
 */
struct inode *v9fs_alloc_inode(struct super_block *sb)
{
        struct v9fs_inode *v9inode;
        v9inode = (struct v9fs_inode *)kmem_cache_alloc(v9fs_inode_cache,
                                                        GFP_KERNEL);
        if (!v9inode)
                return NULL;
#ifdef CONFIG_9P_FSCACHE
        v9inode->fscache = NULL;
        mutex_init(&v9inode->fscache_lock);
#endif
        v9inode->writeback_fid = NULL;
        v9inode->cache_validity = 0;
        mutex_init(&v9inode->v_mutex);
        return &v9inode->vfs_inode;
}

/**
 * v9fs_free_inode - destroy an inode
 *
 */

void v9fs_free_inode(struct inode *inode)
{
        kmem_cache_free(v9fs_inode_cache, V9FS_I(inode));
}

int v9fs_init_inode(struct v9fs_session_info *v9ses,
                    struct inode *inode, umode_t mode, dev_t rdev)
{
        int err = 0;

        inode_init_owner(inode, NULL, mode);
        inode->i_blocks = 0;
        inode->i_rdev = rdev;
        inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
        inode->i_mapping->a_ops = &v9fs_addr_operations;

        switch (mode & S_IFMT) {
        case S_IFIFO:
        case S_IFBLK:
        case S_IFCHR:
        case S_IFSOCK:
                if (v9fs_proto_dotl(v9ses)) {
                        inode->i_op = &v9fs_file_inode_operations_dotl;
                } else if (v9fs_proto_dotu(v9ses)) {
                        inode->i_op = &v9fs_file_inode_operations;
                } else {
                        p9_debug(P9_DEBUG_ERROR,
                                 "special files without extended mode\n");
                        err = -EINVAL;
                        goto error;
                }
                init_special_inode(inode, inode->i_mode, inode->i_rdev);
                break;
        case S_IFREG:
                if (v9fs_proto_dotl(v9ses)) {
                        inode->i_op = &v9fs_file_inode_operations_dotl;
                        if (v9ses->cache == CACHE_LOOSE ||
                            v9ses->cache == CACHE_FSCACHE)
                                inode->i_fop =
                                        &v9fs_cached_file_operations_dotl;
                        else if (v9ses->cache == CACHE_MMAP)
                                inode->i_fop = &v9fs_mmap_file_operations_dotl;
                        else
                                inode->i_fop = &v9fs_file_operations_dotl;
                } else {
                        inode->i_op = &v9fs_file_inode_operations;
                        if (v9ses->cache == CACHE_LOOSE ||
                            v9ses->cache == CACHE_FSCACHE)
                                inode->i_fop =
                                        &v9fs_cached_file_operations;
                        else if (v9ses->cache == CACHE_MMAP)
                                inode->i_fop = &v9fs_mmap_file_operations;
                        else
                                inode->i_fop = &v9fs_file_operations;
                }

                break;
        case S_IFLNK:
                if (!v9fs_proto_dotu(v9ses) && !v9fs_proto_dotl(v9ses)) {
                        p9_debug(P9_DEBUG_ERROR,
                                 "extended modes used with legacy protocol\n");
                        err = -EINVAL;
                        goto error;
                }

                if (v9fs_proto_dotl(v9ses))
                        inode->i_op = &v9fs_symlink_inode_operations_dotl;
                else
                        inode->i_op = &v9fs_symlink_inode_operations;

                break;
        case S_IFDIR:
                inc_nlink(inode);
                if (v9fs_proto_dotl(v9ses))
                        inode->i_op = &v9fs_dir_inode_operations_dotl;
                else if (v9fs_proto_dotu(v9ses))
                        inode->i_op = &v9fs_dir_inode_operations_dotu;
                else
                        inode->i_op = &v9fs_dir_inode_operations;

                if (v9fs_proto_dotl(v9ses))
                        inode->i_fop = &v9fs_dir_operations_dotl;
                else
                        inode->i_fop = &v9fs_dir_operations;

                break;
        default:
                p9_debug(P9_DEBUG_ERROR, "BAD mode 0x%hx S_IFMT 0x%x\n",
                         mode, mode & S_IFMT);
                err = -EINVAL;
                goto error;
        }
error:
        return err;

}

/**
 * v9fs_get_inode - helper function to setup an inode
 * @sb: superblock
 * @mode: mode to setup inode with
 *
 */

struct inode *v9fs_get_inode(struct super_block *sb, umode_t mode, dev_t rdev)
{
        int err;
        struct inode *inode;
        struct v9fs_session_info *v9ses = sb->s_fs_info;

        p9_debug(P9_DEBUG_VFS, "super block: %p mode: %ho\n", sb, mode);

        inode = new_inode(sb);
        if (!inode) {
                pr_warn("%s (%d): Problem allocating inode\n",
                        __func__, task_pid_nr(current));
                return ERR_PTR(-ENOMEM);
        }
        err = v9fs_init_inode(v9ses, inode, mode, rdev);
        if (err) {
                iput(inode);
                return ERR_PTR(err);
        }
        return inode;
}

/*
static struct v9fs_fid*
v9fs_clone_walk(struct v9fs_session_info *v9ses, u32 fid, struct dentry *dentry)
{
        int err;
        int nfid;
        struct v9fs_fid *ret;
        struct v9fs_fcall *fcall;

        nfid = v9fs_get_idpool(&v9ses->fidpool);
        if (nfid < 0) {
                eprintk(KERN_WARNING, "no free fids available\n");
                return ERR_PTR(-ENOSPC);
        }

        err = v9fs_t_walk(v9ses, fid, nfid, (char *) dentry->d_name.name,
                &fcall);

        if (err < 0) {
                if (fcall && fcall->id == RWALK)
                        goto clunk_fid;

                PRINT_FCALL_ERROR("walk error", fcall);
                v9fs_put_idpool(nfid, &v9ses->fidpool);
                goto error;
        }

        kfree(fcall);
        fcall = NULL;
        ret = v9fs_fid_create(v9ses, nfid);
        if (!ret) {
                err = -ENOMEM;
                goto clunk_fid;
        }

        err = v9fs_fid_insert(ret, dentry);
        if (err < 0) {
                v9fs_fid_destroy(ret);
                goto clunk_fid;
        }

        return ret;

clunk_fid:
        v9fs_t_clunk(v9ses, nfid);

error:
        kfree(fcall);
        return ERR_PTR(err);
}
*/


/**
 * v9fs_clear_inode - release an inode
 * @inode: inode to release
 *
 */
void v9fs_evict_inode(struct inode *inode)
{
        struct v9fs_inode *v9inode = V9FS_I(inode);

        truncate_inode_pages_final(&inode->i_data);
        clear_inode(inode);
        filemap_fdatawrite(&inode->i_data);

        v9fs_cache_inode_put_cookie(inode);
        /* clunk the fid stashed in writeback_fid */
        if (v9inode->writeback_fid) {
                p9_client_clunk(v9inode->writeback_fid);
                v9inode->writeback_fid = NULL;
        }
}

static int v9fs_test_inode(struct inode *inode, void *data)
{
        int umode;
        dev_t rdev;
        struct v9fs_inode *v9inode = V9FS_I(inode);
        struct p9_wstat *st = (struct p9_wstat *)data;
        struct v9fs_session_info *v9ses = v9fs_inode2v9ses(inode);

        umode = p9mode2unixmode(v9ses, st, &rdev);
        /* don't match inode of different type */
        if ((inode->i_mode & S_IFMT) != (umode & S_IFMT))
                return 0;

        /* compare qid details */
        if (memcmp(&v9inode->qid.version,
                   &st->qid.version, sizeof(v9inode->qid.version)))
                return 0;

        if (v9inode->qid.type != st->qid.type)
                return 0;

        if (v9inode->qid.path != st->qid.path)
                return 0;
        return 1;
}

static int v9fs_test_new_inode(struct inode *inode, void *data)
{
        return 0;
}

static int v9fs_set_inode(struct inode *inode,  void *data)
{
        struct v9fs_inode *v9inode = V9FS_I(inode);
        struct p9_wstat *st = (struct p9_wstat *)data;

        memcpy(&v9inode->qid, &st->qid, sizeof(st->qid));
        return 0;
}

static struct inode *v9fs_qid_iget(struct super_block *sb,
                                   struct p9_qid *qid,
                                   struct p9_wstat *st,
                                   int new)
{
        dev_t rdev;
        int retval;
        umode_t umode;
        unsigned long i_ino;
        struct inode *inode;
        struct v9fs_session_info *v9ses = sb->s_fs_info;
        int (*test)(struct inode *, void *);

        if (new)
                test = v9fs_test_new_inode;
        else
                test = v9fs_test_inode;

        i_ino = v9fs_qid2ino(qid);
        inode = iget5_locked(sb, i_ino, test, v9fs_set_inode, st);
        if (!inode)
                return ERR_PTR(-ENOMEM);
        if (!(inode->i_state & I_NEW))
                return inode;
        /*
         * initialize the inode with the stat info
         * FIXME!! we may need support for stale inodes
         * later.
         */
        inode->i_ino = i_ino;
        umode = p9mode2unixmode(v9ses, st, &rdev);
        retval = v9fs_init_inode(v9ses, inode, umode, rdev);
        if (retval)
                goto error;

        v9fs_stat2inode(st, inode, sb, 0);
        v9fs_cache_inode_get_cookie(inode);
        unlock_new_inode(inode);
        return inode;
error:
        iget_failed(inode);
        return ERR_PTR(retval);

}

struct inode *
v9fs_inode_from_fid(struct v9fs_session_info *v9ses, struct p9_fid *fid,
                    struct super_block *sb, int new)
{
        struct p9_wstat *st;
        struct inode *inode = NULL;

        st = p9_client_stat(fid);
        if (IS_ERR(st))
                return ERR_CAST(st);

        inode = v9fs_qid_iget(sb, &st->qid, st, new);
        p9stat_free(st);
        kfree(st);
        return inode;
}

/**
 * v9fs_at_to_dotl_flags- convert Linux specific AT flags to
 * plan 9 AT flag.
 * @flags: flags to convert
 */
static int v9fs_at_to_dotl_flags(int flags)
{
        int rflags = 0;
        if (flags & AT_REMOVEDIR)
                rflags |= P9_DOTL_AT_REMOVEDIR;
        return rflags;
}

/**
 * v9fs_dec_count - helper functon to drop i_nlink.
 *
 * If a directory had nlink <= 2 (including . and ..), then we should not drop
 * the link count, which indicates the underlying exported fs doesn't maintain
 * nlink accurately. e.g.
 * - overlayfs sets nlink to 1 for merged dir
 * - ext4 (with dir_nlink feature enabled) sets nlink to 1 if a dir has more
 *   than EXT4_LINK_MAX (65000) links.
 *
 * @inode: inode whose nlink is being dropped
 */
static void v9fs_dec_count(struct inode *inode)
{
        if (!S_ISDIR(inode->i_mode) || inode->i_nlink > 2)
                drop_nlink(inode);
}

/**
 * v9fs_remove - helper function to remove files and directories
 * @dir: directory inode that is being deleted
 * @dentry:  dentry that is being deleted
 * @flags: removing a directory
 *
 */

static int v9fs_remove(struct inode *dir, struct dentry *dentry, int flags)
{
        struct inode *inode;
        int retval = -EOPNOTSUPP;
        struct p9_fid *v9fid, *dfid;
        struct v9fs_session_info *v9ses;

        p9_debug(P9_DEBUG_VFS, "inode: %p dentry: %p rmdir: %x\n",
                 dir, dentry, flags);

        v9ses = v9fs_inode2v9ses(dir);
        inode = d_inode(dentry);
        dfid = v9fs_parent_fid(dentry);
        if (IS_ERR(dfid)) {
                retval = PTR_ERR(dfid);
                p9_debug(P9_DEBUG_VFS, "fid lookup failed %d\n", retval);
                return retval;
        }
        if (v9fs_proto_dotl(v9ses))
                retval = p9_client_unlinkat(dfid, dentry->d_name.name,
                                            v9fs_at_to_dotl_flags(flags));
        if (retval == -EOPNOTSUPP) {
                /* Try the one based on path */
                v9fid = v9fs_fid_clone(dentry);
                if (IS_ERR(v9fid))
                        return PTR_ERR(v9fid);
                retval = p9_client_remove(v9fid);
        }
        if (!retval) {
                /*
                 * directories on unlink should have zero
                 * link count
                 */
                if (flags & AT_REMOVEDIR) {
                        clear_nlink(inode);
                        v9fs_dec_count(dir);
                } else
                        v9fs_dec_count(inode);

                v9fs_invalidate_inode_attr(inode);
                v9fs_invalidate_inode_attr(dir);
        }
        return retval;
}

/**
 * v9fs_create - Create a file
 * @v9ses: session information
 * @dir: directory that dentry is being created in
 * @dentry:  dentry that is being created
 * @extension: 9p2000.u extension string to support devices, etc.
 * @perm: create permissions
 * @mode: open mode
 *
 */
static struct p9_fid *
v9fs_create(struct v9fs_session_info *v9ses, struct inode *dir,
                struct dentry *dentry, char *extension, u32 perm, u8 mode)
{
        int err;
        const unsigned char *name;
        struct p9_fid *dfid, *ofid, *fid;
        struct inode *inode;

        p9_debug(P9_DEBUG_VFS, "name %pd\n", dentry);

        err = 0;
        ofid = NULL;
        fid = NULL;
        name = dentry->d_name.name;
        dfid = v9fs_parent_fid(dentry);
        if (IS_ERR(dfid)) {
                err = PTR_ERR(dfid);
                p9_debug(P9_DEBUG_VFS, "fid lookup failed %d\n", err);
                return ERR_PTR(err);
        }

        /* clone a fid to use for creation */
        ofid = clone_fid(dfid);
        if (IS_ERR(ofid)) {
                err = PTR_ERR(ofid);
                p9_debug(P9_DEBUG_VFS, "p9_client_walk failed %d\n", err);
                return ERR_PTR(err);
        }

        err = p9_client_fcreate(ofid, name, perm, mode, extension);
        if (err < 0) {
                p9_debug(P9_DEBUG_VFS, "p9_client_fcreate failed %d\n", err);
                goto error;
        }

        if (!(perm & P9_DMLINK)) {
                /* now walk from the parent so we can get unopened fid */
                fid = p9_client_walk(dfid, 1, &name, 1);
                if (IS_ERR(fid)) {
                        err = PTR_ERR(fid);
                        p9_debug(P9_DEBUG_VFS,
                                   "p9_client_walk failed %d\n", err);
                        fid = NULL;
                        goto error;
                }
                /*
                 * instantiate inode and assign the unopened fid to the dentry
                 */
                inode = v9fs_get_new_inode_from_fid(v9ses, fid, dir->i_sb);
                if (IS_ERR(inode)) {
                        err = PTR_ERR(inode);
                        p9_debug(P9_DEBUG_VFS,
                                   "inode creation failed %d\n", err);
                        goto error;
                }
                v9fs_fid_add(dentry, fid);
                d_instantiate(dentry, inode);
        }
        return ofid;
error:
        if (ofid)
                p9_client_clunk(ofid);

        if (fid)
                p9_client_clunk(fid);

        return ERR_PTR(err);
}

/**
 * v9fs_vfs_create - VFS hook to create a regular file
 *
 * open(.., O_CREAT) is handled in v9fs_vfs_atomic_open().  This is only called
 * for mknod(2).
 *
 * @dir: directory inode that is being created
 * @dentry:  dentry that is being deleted
 * @mode: create permissions
 *
 */

static int
v9fs_vfs_create(struct inode *dir, struct dentry *dentry, umode_t mode,
                bool excl)
{
        struct v9fs_session_info *v9ses = v9fs_inode2v9ses(dir);
        u32 perm = unixmode2p9mode(v9ses, mode);
        struct p9_fid *fid;

        /* P9_OEXCL? */
        fid = v9fs_create(v9ses, dir, dentry, NULL, perm, P9_ORDWR);
        if (IS_ERR(fid))
                return PTR_ERR(fid);

        v9fs_invalidate_inode_attr(dir);
        p9_client_clunk(fid);

        return 0;
}

/**
 * v9fs_vfs_mkdir - VFS mkdir hook to create a directory
 * @dir:  inode that is being unlinked
 * @dentry: dentry that is being unlinked
 * @mode: mode for new directory
 *
 */

static int v9fs_vfs_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
{
        int err;
        u32 perm;
        struct p9_fid *fid;
        struct v9fs_session_info *v9ses;

        p9_debug(P9_DEBUG_VFS, "name %pd\n", dentry);
        err = 0;
        v9ses = v9fs_inode2v9ses(dir);
        perm = unixmode2p9mode(v9ses, mode | S_IFDIR);
        fid = v9fs_create(v9ses, dir, dentry, NULL, perm, P9_OREAD);
        if (IS_ERR(fid)) {
                err = PTR_ERR(fid);
                fid = NULL;
        } else {
                inc_nlink(dir);
                v9fs_invalidate_inode_attr(dir);
        }

        if (fid)
                p9_client_clunk(fid);

        return err;
}

/**
 * v9fs_vfs_lookup - VFS lookup hook to "walk" to a new inode
 * @dir:  inode that is being walked from
 * @dentry: dentry that is being walked to?
 * @flags: lookup flags (unused)
 *
 */

struct dentry *v9fs_vfs_lookup(struct inode *dir, struct dentry *dentry,
                                      unsigned int flags)
{
        struct dentry *res;
        struct v9fs_session_info *v9ses;
        struct p9_fid *dfid, *fid;
        struct inode *inode;
        const unsigned char *name;

        p9_debug(P9_DEBUG_VFS, "dir: %p dentry: (%pd) %p flags: %x\n",
                 dir, dentry, dentry, flags);

        if (dentry->d_name.len > NAME_MAX)
                return ERR_PTR(-ENAMETOOLONG);

        v9ses = v9fs_inode2v9ses(dir);
        /* We can walk d_parent because we hold the dir->i_mutex */
        dfid = v9fs_parent_fid(dentry);
        if (IS_ERR(dfid))
                return ERR_CAST(dfid);

        /*
         * Make sure we don't use a wrong inode due to parallel
         * unlink. For cached mode create calls request for new
         * inode. But with cache disabled, lookup should do this.
         */
        name = dentry->d_name.name;
        fid = p9_client_walk(dfid, 1, &name, 1);
        if (fid == ERR_PTR(-ENOENT))
                inode = NULL;
        else if (IS_ERR(fid))
                inode = ERR_CAST(fid);
        else if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE)
                inode = v9fs_get_inode_from_fid(v9ses, fid, dir->i_sb);
        else
                inode = v9fs_get_new_inode_from_fid(v9ses, fid, dir->i_sb);
        /*
         * If we had a rename on the server and a parallel lookup
         * for the new name, then make sure we instantiate with
         * the new name. ie look up for a/b, while on server somebody
         * moved b under k and client parallely did a lookup for
         * k/b.
         */
        res = d_splice_alias(inode, dentry);
        if (!IS_ERR(fid)) {
                if (!res)
                        v9fs_fid_add(dentry, fid);
                else if (!IS_ERR(res))
                        v9fs_fid_add(res, fid);
                else
                        p9_client_clunk(fid);
        }
        return res;
}

static int
v9fs_vfs_atomic_open(struct inode *dir, struct dentry *dentry,
                     struct file *file, unsigned flags, umode_t mode)
{
        int err;
        u32 perm;
        struct v9fs_inode *v9inode;
        struct v9fs_session_info *v9ses;
        struct p9_fid *fid, *inode_fid;
        struct dentry *res = NULL;

        if (d_in_lookup(dentry)) {
                res = v9fs_vfs_lookup(dir, dentry, 0);
                if (IS_ERR(res))
                        return PTR_ERR(res);

                if (res)
                        dentry = res;
        }

        /* Only creates */
        if (!(flags & O_CREAT) || d_really_is_positive(dentry))
                return finish_no_open(file, res);

        err = 0;

        v9ses = v9fs_inode2v9ses(dir);
        perm = unixmode2p9mode(v9ses, mode);
        fid = v9fs_create(v9ses, dir, dentry, NULL, perm,
                                v9fs_uflags2omode(flags,
                                                v9fs_proto_dotu(v9ses)));
        if (IS_ERR(fid)) {
                err = PTR_ERR(fid);
                fid = NULL;
                goto error;
        }

        v9fs_invalidate_inode_attr(dir);
        v9inode = V9FS_I(d_inode(dentry));
        mutex_lock(&v9inode->v_mutex);
        if ((v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE) &&
            !v9inode->writeback_fid &&
            ((flags & O_ACCMODE) != O_RDONLY)) {
                /*
                 * clone a fid and add it to writeback_fid
                 * we do it during open time instead of
                 * page dirty time via write_begin/page_mkwrite
                 * because we want write after unlink usecase
                 * to work.
                 */
                inode_fid = v9fs_writeback_fid(dentry);
                if (IS_ERR(inode_fid)) {
                        err = PTR_ERR(inode_fid);
                        mutex_unlock(&v9inode->v_mutex);
                        goto error;
                }
                v9inode->writeback_fid = (void *) inode_fid;
        }
        mutex_unlock(&v9inode->v_mutex);
        err = finish_open(file, dentry, generic_file_open);
        if (err)
                goto error;

        file->private_data = fid;
        if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE)
                v9fs_cache_inode_set_cookie(d_inode(dentry), file);

        file->f_mode |= FMODE_CREATED;
out:
        dput(res);
        return err;

error:
        if (fid)
                p9_client_clunk(fid);
        goto out;
}

/**
 * v9fs_vfs_unlink - VFS unlink hook to delete an inode
 * @i:  inode that is being unlinked
 * @d: dentry that is being unlinked
 *
 */

int v9fs_vfs_unlink(struct inode *i, struct dentry *d)
{
        return v9fs_remove(i, d, 0);
}

/**
 * v9fs_vfs_rmdir - VFS unlink hook to delete a directory
 * @i:  inode that is being unlinked
 * @d: dentry that is being unlinked
 *
 */

int v9fs_vfs_rmdir(struct inode *i, struct dentry *d)
{
        return v9fs_remove(i, d, AT_REMOVEDIR);
}

/**
 * v9fs_vfs_rename - VFS hook to rename an inode
 * @old_dir:  old dir inode
 * @old_dentry: old dentry
 * @new_dir: new dir inode
 * @new_dentry: new dentry
 *
 */

int
v9fs_vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
                struct inode *new_dir, struct dentry *new_dentry,
                unsigned int flags)
{
        int retval;
        struct inode *old_inode;
        struct inode *new_inode;
        struct v9fs_session_info *v9ses;
        struct p9_fid *oldfid;
        struct p9_fid *olddirfid;
        struct p9_fid *newdirfid;
        struct p9_wstat wstat;

        if (flags)
                return -EINVAL;

        p9_debug(P9_DEBUG_VFS, "\n");
        retval = 0;
        old_inode = d_inode(old_dentry);
        new_inode = d_inode(new_dentry);
        v9ses = v9fs_inode2v9ses(old_inode);
        oldfid = v9fs_fid_lookup(old_dentry);
        if (IS_ERR(oldfid))
                return PTR_ERR(oldfid);

        olddirfid = clone_fid(v9fs_parent_fid(old_dentry));
        if (IS_ERR(olddirfid)) {
                retval = PTR_ERR(olddirfid);
                goto done;
        }

        newdirfid = clone_fid(v9fs_parent_fid(new_dentry));
        if (IS_ERR(newdirfid)) {
                retval = PTR_ERR(newdirfid);
                goto clunk_olddir;
        }

        down_write(&v9ses->rename_sem);
        if (v9fs_proto_dotl(v9ses)) {
                retval = p9_client_renameat(olddirfid, old_dentry->d_name.name,
                                            newdirfid, new_dentry->d_name.name);
                if (retval == -EOPNOTSUPP)
                        retval = p9_client_rename(oldfid, newdirfid,
                                                  new_dentry->d_name.name);
                if (retval != -EOPNOTSUPP)
                        goto clunk_newdir;
        }
        if (old_dentry->d_parent != new_dentry->d_parent) {
                /*
                 * 9P .u can only handle file rename in the same directory

                 */

                p9_debug(P9_DEBUG_ERROR, "old dir and new dir are different\n");
                retval = -EXDEV;
                goto clunk_newdir;
        }
        v9fs_blank_wstat(&wstat);
        wstat.muid = v9ses->uname;
        wstat.name = new_dentry->d_name.name;
        retval = p9_client_wstat(oldfid, &wstat);

clunk_newdir:
        if (!retval) {
                if (new_inode) {
                        if (S_ISDIR(new_inode->i_mode))
                                clear_nlink(new_inode);
                        else
                                v9fs_dec_count(new_inode);
                }
                if (S_ISDIR(old_inode->i_mode)) {
                        if (!new_inode)
                                inc_nlink(new_dir);
                        v9fs_dec_count(old_dir);
                }
                v9fs_invalidate_inode_attr(old_inode);
                v9fs_invalidate_inode_attr(old_dir);
                v9fs_invalidate_inode_attr(new_dir);

                /* successful rename */
                d_move(old_dentry, new_dentry);
        }
        up_write(&v9ses->rename_sem);
        p9_client_clunk(newdirfid);

clunk_olddir:
        p9_client_clunk(olddirfid);

done:
        return retval;
}

/**
 * v9fs_vfs_getattr - retrieve file metadata
 * @path: Object to query
 * @stat: metadata structure to populate
 * @request_mask: Mask of STATX_xxx flags indicating the caller's interests
 * @flags: AT_STATX_xxx setting
 *
 */

static int
v9fs_vfs_getattr(const struct path *path, struct kstat *stat,
                 u32 request_mask, unsigned int flags)
{
        struct dentry *dentry = path->dentry;
        struct v9fs_session_info *v9ses;
        struct p9_fid *fid;
        struct p9_wstat *st;

        p9_debug(P9_DEBUG_VFS, "dentry: %p\n", dentry);
        v9ses = v9fs_dentry2v9ses(dentry);
        if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE) {
                generic_fillattr(d_inode(dentry), stat);
                return 0;
        }
        fid = v9fs_fid_lookup(dentry);
        if (IS_ERR(fid))
                return PTR_ERR(fid);

        st = p9_client_stat(fid);
        if (IS_ERR(st))
                return PTR_ERR(st);

        v9fs_stat2inode(st, d_inode(dentry), dentry->d_sb, 0);
        generic_fillattr(d_inode(dentry), stat);

        p9stat_free(st);
        kfree(st);
        return 0;
}

/**
 * v9fs_vfs_setattr - set file metadata
 * @dentry: file whose metadata to set
 * @iattr: metadata assignment structure
 *
 */

static int v9fs_vfs_setattr(struct dentry *dentry, struct iattr *iattr)
{
        int retval;
        struct v9fs_session_info *v9ses;
        struct p9_fid *fid;
        struct p9_wstat wstat;

        p9_debug(P9_DEBUG_VFS, "\n");
        retval = setattr_prepare(dentry, iattr);
        if (retval)
                return retval;

        retval = -EPERM;
        v9ses = v9fs_dentry2v9ses(dentry);
        fid = v9fs_fid_lookup(dentry);
        if(IS_ERR(fid))
                return PTR_ERR(fid);

        v9fs_blank_wstat(&wstat);
        if (iattr->ia_valid & ATTR_MODE)
                wstat.mode = unixmode2p9mode(v9ses, iattr->ia_mode);

        if (iattr->ia_valid & ATTR_MTIME)
                wstat.mtime = iattr->ia_mtime.tv_sec;

        if (iattr->ia_valid & ATTR_ATIME)
                wstat.atime = iattr->ia_atime.tv_sec;

        if (iattr->ia_valid & ATTR_SIZE)
                wstat.length = iattr->ia_size;

        if (v9fs_proto_dotu(v9ses)) {
                if (iattr->ia_valid & ATTR_UID)
                        wstat.n_uid = iattr->ia_uid;

                if (iattr->ia_valid & ATTR_GID)
                        wstat.n_gid = iattr->ia_gid;
        }

        /* Write all dirty data */
        if (d_is_reg(dentry))
                filemap_write_and_wait(d_inode(dentry)->i_mapping);

        retval = p9_client_wstat(fid, &wstat);
        if (retval < 0)
                return retval;

        if ((iattr->ia_valid & ATTR_SIZE) &&
            iattr->ia_size != i_size_read(d_inode(dentry)))
                truncate_setsize(d_inode(dentry), iattr->ia_size);

        v9fs_invalidate_inode_attr(d_inode(dentry));

        setattr_copy(d_inode(dentry), iattr);
        mark_inode_dirty(d_inode(dentry));
        return 0;
}

/**
 * v9fs_stat2inode - populate an inode structure with mistat info
 * @stat: Plan 9 metadata (mistat) structure
 * @inode: inode to populate
 * @sb: superblock of filesystem
 * @flags: control flags (e.g. V9FS_STAT2INODE_KEEP_ISIZE)
 *
 */

void
v9fs_stat2inode(struct p9_wstat *stat, struct inode *inode,
                 struct super_block *sb, unsigned int flags)
{
        umode_t mode;
        char ext[32];
        char tag_name[14];
        unsigned int i_nlink;
        struct v9fs_session_info *v9ses = sb->s_fs_info;
        struct v9fs_inode *v9inode = V9FS_I(inode);

        set_nlink(inode, 1);

        inode->i_atime.tv_sec = stat->atime;
        inode->i_mtime.tv_sec = stat->mtime;
        inode->i_ctime.tv_sec = stat->mtime;

        inode->i_uid = v9ses->dfltuid;
        inode->i_gid = v9ses->dfltgid;

        if (v9fs_proto_dotu(v9ses)) {
                inode->i_uid = stat->n_uid;
                inode->i_gid = stat->n_gid;
        }
        if ((S_ISREG(inode->i_mode)) || (S_ISDIR(inode->i_mode))) {
                if (v9fs_proto_dotu(v9ses) && (stat->extension[0] != '\0')) {
                        /*
                         * Hadlink support got added later to
                         * to the .u extension. So there can be
                         * server out there that doesn't support
                         * this even with .u extension. So check
                         * for non NULL stat->extension
                         */
                        strlcpy(ext, stat->extension, sizeof(ext));
                        /* HARDLINKCOUNT %u */
                        sscanf(ext, "%13s %u", tag_name, &i_nlink);
                        if (!strncmp(tag_name, "HARDLINKCOUNT", 13))
                                set_nlink(inode, i_nlink);
                }
        }
        mode = p9mode2perm(v9ses, stat);
        mode |= inode->i_mode & ~S_IALLUGO;
        inode->i_mode = mode;

        if (!(flags & V9FS_STAT2INODE_KEEP_ISIZE))
                v9fs_i_size_write(inode, stat->length);
        /* not real number of blocks, but 512 byte ones ... */
        inode->i_blocks = (stat->length + 512 - 1) >> 9;
        v9inode->cache_validity &= ~V9FS_INO_INVALID_ATTR;
}

/**
 * v9fs_qid2ino - convert qid into inode number
 * @qid: qid to hash
 *
 * BUG: potential for inode number collisions?
 */

ino_t v9fs_qid2ino(struct p9_qid *qid)
{
        u64 path = qid->path + 2;
        ino_t i = 0;

        if (sizeof(ino_t) == sizeof(path))
                memcpy(&i, &path, sizeof(ino_t));
        else
                i = (ino_t) (path ^ (path >> 32));

        return i;
}

/**
 * v9fs_vfs_get_link - follow a symlink path
 * @dentry: dentry for symlink
 * @inode: inode for symlink
 * @done: delayed call for when we are done with the return value
 */

static const char *v9fs_vfs_get_link(struct dentry *dentry,
                                     struct inode *inode,
                                     struct delayed_call *done)
{
        struct v9fs_session_info *v9ses;
        struct p9_fid *fid;
        struct p9_wstat *st;
        char *res;

        if (!dentry)
                return ERR_PTR(-ECHILD);

        v9ses = v9fs_dentry2v9ses(dentry);
        fid = v9fs_fid_lookup(dentry);
        p9_debug(P9_DEBUG_VFS, "%pd\n", dentry);

        if (IS_ERR(fid))
                return ERR_CAST(fid);

        if (!v9fs_proto_dotu(v9ses))
                return ERR_PTR(-EBADF);

        st = p9_client_stat(fid);
        if (IS_ERR(st))
                return ERR_CAST(st);

        if (!(st->mode & P9_DMSYMLINK)) {
                p9stat_free(st);
                kfree(st);
                return ERR_PTR(-EINVAL);
        }
        res = st->extension;
        st->extension = NULL;
        if (strlen(res) >= PATH_MAX)
                res[PATH_MAX - 1] = '\0';

        p9stat_free(st);
        kfree(st);
        set_delayed_call(done, kfree_link, res);
        return res;
}

/**
 * v9fs_vfs_mkspecial - create a special file
 * @dir: inode to create special file in
 * @dentry: dentry to create
 * @perm: mode to create special file
 * @extension: 9p2000.u format extension string representing special file
 *
 */

static int v9fs_vfs_mkspecial(struct inode *dir, struct dentry *dentry,
        u32 perm, const char *extension)
{
        struct p9_fid *fid;
        struct v9fs_session_info *v9ses;

        v9ses = v9fs_inode2v9ses(dir);
        if (!v9fs_proto_dotu(v9ses)) {
                p9_debug(P9_DEBUG_ERROR, "not extended\n");
                return -EPERM;
        }

        fid = v9fs_create(v9ses, dir, dentry, (char *) extension, perm,
                                                                P9_OREAD);
        if (IS_ERR(fid))
                return PTR_ERR(fid);

        v9fs_invalidate_inode_attr(dir);
        p9_client_clunk(fid);
        return 0;
}

/**
 * v9fs_vfs_symlink - helper function to create symlinks
 * @dir: directory inode containing symlink
 * @dentry: dentry for symlink
 * @symname: symlink data
 *
 * See Also: 9P2000.u RFC for more information
 *
 */

static int
v9fs_vfs_symlink(struct inode *dir, struct dentry *dentry, const char *symname)
{
        p9_debug(P9_DEBUG_VFS, " %lu,%pd,%s\n",
                 dir->i_ino, dentry, symname);

        return v9fs_vfs_mkspecial(dir, dentry, P9_DMSYMLINK, symname);
}

#define U32_MAX_DIGITS 10

/**
 * v9fs_vfs_link - create a hardlink
 * @old_dentry: dentry for file to link to
 * @dir: inode destination for new link
 * @dentry: dentry for link
 *
 */

static int
v9fs_vfs_link(struct dentry *old_dentry, struct inode *dir,
              struct dentry *dentry)
{
        int retval;
        char name[1 + U32_MAX_DIGITS + 2]; /* sign + number + \n + \0 */
        struct p9_fid *oldfid;

        p9_debug(P9_DEBUG_VFS, " %lu,%pd,%pd\n",
                 dir->i_ino, dentry, old_dentry);

        oldfid = v9fs_fid_clone(old_dentry);
        if (IS_ERR(oldfid))
                return PTR_ERR(oldfid);

        sprintf(name, "%d\n", oldfid->fid);
        retval = v9fs_vfs_mkspecial(dir, dentry, P9_DMLINK, name);
        if (!retval) {
                v9fs_refresh_inode(oldfid, d_inode(old_dentry));
                v9fs_invalidate_inode_attr(dir);
        }
        p9_client_clunk(oldfid);
        return retval;
}

/**
 * v9fs_vfs_mknod - create a special file
 * @dir: inode destination for new link
 * @dentry: dentry for file
 * @mode: mode for creation
 * @rdev: device associated with special file
 *
 */

static int
v9fs_vfs_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t rdev)
{
        struct v9fs_session_info *v9ses = v9fs_inode2v9ses(dir);
        int retval;
        char name[2 + U32_MAX_DIGITS + 1 + U32_MAX_DIGITS + 1];
        u32 perm;

        p9_debug(P9_DEBUG_VFS, " %lu,%pd mode: %hx MAJOR: %u MINOR: %u\n",
                 dir->i_ino, dentry, mode,
                 MAJOR(rdev), MINOR(rdev));

        /* build extension */
        if (S_ISBLK(mode))
                sprintf(name, "b %u %u", MAJOR(rdev), MINOR(rdev));
        else if (S_ISCHR(mode))
                sprintf(name, "c %u %u", MAJOR(rdev), MINOR(rdev));
        else
                *name = 0;

        perm = unixmode2p9mode(v9ses, mode);
        retval = v9fs_vfs_mkspecial(dir, dentry, perm, name);

        return retval;
}

int v9fs_refresh_inode(struct p9_fid *fid, struct inode *inode)
{
        int umode;
        dev_t rdev;
        struct p9_wstat *st;
        struct v9fs_session_info *v9ses;
        unsigned int flags;

        v9ses = v9fs_inode2v9ses(inode);
        st = p9_client_stat(fid);
        if (IS_ERR(st))
                return PTR_ERR(st);
        /*
         * Don't update inode if the file type is different
         */
        umode = p9mode2unixmode(v9ses, st, &rdev);
        if ((inode->i_mode & S_IFMT) != (umode & S_IFMT))
                goto out;

        /*
         * We don't want to refresh inode->i_size,
         * because we may have cached data
         */
        flags = (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE) ?
                V9FS_STAT2INODE_KEEP_ISIZE : 0;
        v9fs_stat2inode(st, inode, inode->i_sb, flags);
out:
        p9stat_free(st);
        kfree(st);
        return 0;
}

static const struct inode_operations v9fs_dir_inode_operations_dotu = {
        .create = v9fs_vfs_create,
        .lookup = v9fs_vfs_lookup,
        .atomic_open = v9fs_vfs_atomic_open,
        .symlink = v9fs_vfs_symlink,
        .link = v9fs_vfs_link,
        .unlink = v9fs_vfs_unlink,
        .mkdir = v9fs_vfs_mkdir,
        .rmdir = v9fs_vfs_rmdir,
        .mknod = v9fs_vfs_mknod,
        .rename = v9fs_vfs_rename,
        .getattr = v9fs_vfs_getattr,
        .setattr = v9fs_vfs_setattr,
};

static const struct inode_operations v9fs_dir_inode_operations = {
        .create = v9fs_vfs_create,
        .lookup = v9fs_vfs_lookup,
        .atomic_open = v9fs_vfs_atomic_open,
        .unlink = v9fs_vfs_unlink,
        .mkdir = v9fs_vfs_mkdir,
        .rmdir = v9fs_vfs_rmdir,
        .mknod = v9fs_vfs_mknod,
        .rename = v9fs_vfs_rename,
        .getattr = v9fs_vfs_getattr,
        .setattr = v9fs_vfs_setattr,
};

static const struct inode_operations v9fs_file_inode_operations = {
        .getattr = v9fs_vfs_getattr,
        .setattr = v9fs_vfs_setattr,
};

static const struct inode_operations v9fs_symlink_inode_operations = {
        .get_link = v9fs_vfs_get_link,
        .getattr = v9fs_vfs_getattr,
        .setattr = v9fs_vfs_setattr,
};