/*
 * fs/logfs/dir.c       - directory-related code
 *
 * As should be obvious for Linux kernel code, license is GPLv2
 *
 * Copyright (c) 2005-2008 Joern Engel <joern@logfs.org>
 */
#include "logfs.h"
#include <linux/slab.h>

/*
 * Atomic dir operations
 *
 * Directory operations are by default not atomic.  Dentries and Inodes are
 * created/removed/altered in separate operations.  Therefore we need to do
 * a small amount of journaling.
 *
 * Create, link, mkdir, mknod and symlink all share the same function to do
 * the work: __logfs_create.  This function works in two atomic steps:
 * 1. allocate inode (remember in journal)
 * 2. allocate dentry (clear journal)
 *
 * As we can only get interrupted between the two, when the inode we just
 * created is simply stored in the anchor.  On next mount, if we were
 * interrupted, we delete the inode.  From a users point of view the
 * operation never happened.
 *
 * Unlink and rmdir also share the same function: unlink.  Again, this
 * function works in two atomic steps
 * 1. remove dentry (remember inode in journal)
 * 2. unlink inode (clear journal)
 *
 * And again, on the next mount, if we were interrupted, we delete the inode.
 * From a users point of view the operation succeeded.
 *
 * Rename is the real pain to deal with, harder than all the other methods
 * combined.  Depending on the circumstances we can run into three cases.
 * A "target rename" where the target dentry already existed, a "local
 * rename" where both parent directories are identical or a "cross-directory
 * rename" in the remaining case.
 *
 * Local rename is atomic, as the old dentry is simply rewritten with a new
 * name.
 *
 * Cross-directory rename works in two steps, similar to __logfs_create and
 * logfs_unlink:
 * 1. Write new dentry (remember old dentry in journal)
 * 2. Remove old dentry (clear journal)
 *
 * Here we remember a dentry instead of an inode.  On next mount, if we were
 * interrupted, we delete the dentry.  From a users point of view, the
 * operation succeeded.
 *
 * Target rename works in three atomic steps:
 * 1. Attach old inode to new dentry (remember old dentry and new inode)
 * 2. Remove old dentry (still remember the new inode)
 * 3. Remove victim inode
 *
 * Here we remember both an inode an a dentry.  If we get interrupted
 * between steps 1 and 2, we delete both the dentry and the inode.  If
 * we get interrupted between steps 2 and 3, we delete just the inode.
 * In either case, the remaining objects are deleted on next mount.  From
 * a users point of view, the operation succeeded.
 */

static int write_dir(struct inode *dir, struct logfs_disk_dentry *dd,
                loff_t pos)
{
        return logfs_inode_write(dir, dd, sizeof(*dd), pos, WF_LOCK, NULL);
}

static int write_inode(struct inode *inode)
{
        return __logfs_write_inode(inode, NULL, WF_LOCK);
}

static s64 dir_seek_data(struct inode *inode, s64 pos)
{
        s64 new_pos = logfs_seek_data(inode, pos);

        return max(pos, new_pos - 1);
}

static int beyond_eof(struct inode *inode, loff_t bix)
{
        loff_t pos = bix << inode->i_sb->s_blocksize_bits;
        return pos >= i_size_read(inode);
}

/*
 * Prime value was chosen to be roughly 256 + 26.  r5 hash uses 11,
 * so short names (len <= 9) don't even occupy the complete 32bit name
 * space.  A prime >256 ensures short names quickly spread the 32bit
 * name space.  Add about 26 for the estimated amount of information
 * of each character and pick a prime nearby, preferably a bit-sparse
 * one.
 */
static u32 hash_32(const char *s, int len, u32 seed)
{
        u32 hash = seed;
        int i;

        for (i = 0; i < len; i++)
                hash = hash * 293 + s[i];
        return hash;
}

/*
 * We have to satisfy several conflicting requirements here.  Small
 * directories should stay fairly compact and not require too many
 * indirect blocks.  The number of possible locations for a given hash
 * should be small to make lookup() fast.  And we should try hard not
 * to overflow the 32bit name space or nfs and 32bit host systems will
 * be unhappy.
 *
 * So we use the following scheme.  First we reduce the hash to 0..15
 * and try a direct block.  If that is occupied we reduce the hash to
 * 16..255 and try an indirect block.  Same for 2x and 3x indirect
 * blocks.  Lastly we reduce the hash to 0x800_0000 .. 0xffff_ffff,
 * but use buckets containing eight entries instead of a single one.
 *
 * Using 16 entries should allow for a reasonable amount of hash
 * collisions, so the 32bit name space can be packed fairly tight
 * before overflowing.  Oh and currently we don't overflow but return
 * and error.
 *
 * How likely are collisions?  Doing the appropriate math is beyond me
 * and the Bronstein textbook.  But running a test program to brute
 * force collisions for a couple of days showed that on average the
 * first collision occurs after 598M entries, with 290M being the
 * smallest result.  Obviously 21 entries could already cause a
 * collision if all entries are carefully chosen.
 */
static pgoff_t hash_index(u32 hash, int round)
{
        u32 i0_blocks = I0_BLOCKS;
        u32 i1_blocks = I1_BLOCKS;
        u32 i2_blocks = I2_BLOCKS;
        u32 i3_blocks = I3_BLOCKS;

        switch (round) {
        case 0:
                return hash % i0_blocks;
        case 1:
                return i0_blocks + hash % (i1_blocks - i0_blocks);
        case 2:
                return i1_blocks + hash % (i2_blocks - i1_blocks);
        case 3:
                return i2_blocks + hash % (i3_blocks - i2_blocks);
        case 4 ... 19:
                return i3_blocks + 16 * (hash % (((1<<31) - i3_blocks) / 16))
                        + round - 4;
        }
        BUG();
}

static struct page *logfs_get_dd_page(struct inode *dir, struct dentry *dentry)
{
        struct qstr *name = &dentry->d_name;
        struct page *page;
        struct logfs_disk_dentry *dd;
        u32 hash = hash_32(name->name, name->len, 0);
        pgoff_t index;
        int round;

        if (name->len > LOGFS_MAX_NAMELEN)
                return ERR_PTR(-ENAMETOOLONG);

        for (round = 0; round < 20; round++) {
                index = hash_index(hash, round);

                if (beyond_eof(dir, index))
                        return NULL;
                if (!logfs_exist_block(dir, index))
                        continue;
                page = read_cache_page(dir->i_mapping, index,
                                (filler_t *)logfs_readpage, NULL);
                if (IS_ERR(page))
                        return page;
                dd = kmap_atomic(page);
                BUG_ON(dd->namelen == 0);

                if (name->len != be16_to_cpu(dd->namelen) ||
                                memcmp(name->name, dd->name, name->len)) {
                        kunmap_atomic(dd);
                        page_cache_release(page);
                        continue;
                }

                kunmap_atomic(dd);
                return page;
        }
        return NULL;
}

static int logfs_remove_inode(struct inode *inode)
{
        int ret;

        drop_nlink(inode);
        ret = write_inode(inode);
        LOGFS_BUG_ON(ret, inode->i_sb);
        return ret;
}

static void abort_transaction(struct inode *inode, struct logfs_transaction *ta)
{
        if (logfs_inode(inode)->li_block)
                logfs_inode(inode)->li_block->ta = NULL;
        kfree(ta);
}

static int logfs_unlink(struct inode *dir, struct dentry *dentry)
{
        struct logfs_super *super = logfs_super(dir->i_sb);
        struct inode *inode = dentry->d_inode;
        struct logfs_transaction *ta;
        struct page *page;
        pgoff_t index;
        int ret;

        ta = kzalloc(sizeof(*ta), GFP_KERNEL);
        if (!ta)
                return -ENOMEM;

        ta->state = UNLINK_1;
        ta->ino = inode->i_ino;

        inode->i_ctime = dir->i_ctime = dir->i_mtime = CURRENT_TIME;

        page = logfs_get_dd_page(dir, dentry);
        if (!page) {
                kfree(ta);
                return -ENOENT;
        }
        if (IS_ERR(page)) {
                kfree(ta);
                return PTR_ERR(page);
        }
        index = page->index;
        page_cache_release(page);

        mutex_lock(&super->s_dirop_mutex);
        logfs_add_transaction(dir, ta);

        ret = logfs_delete(dir, index, NULL);
        if (!ret)
                ret = write_inode(dir);

        if (ret) {
                abort_transaction(dir, ta);
                printk(KERN_ERR"LOGFS: unable to delete inode\n");
                goto out;
        }

        ta->state = UNLINK_2;
        logfs_add_transaction(inode, ta);
        ret = logfs_remove_inode(inode);
out:
        mutex_unlock(&super->s_dirop_mutex);
        return ret;
}

static inline int logfs_empty_dir(struct inode *dir)
{
        u64 data;

        data = logfs_seek_data(dir, 0) << dir->i_sb->s_blocksize_bits;
        return data >= i_size_read(dir);
}

static int logfs_rmdir(struct inode *dir, struct dentry *dentry)
{
        struct inode *inode = dentry->d_inode;

        if (!logfs_empty_dir(inode))
                return -ENOTEMPTY;

        return logfs_unlink(dir, dentry);
}

/* FIXME: readdir currently has it's own dir_walk code.  I don't see a good
 * way to combine the two copies */
static int logfs_readdir(struct file *file, struct dir_context *ctx)
{
        struct inode *dir = file_inode(file);
        loff_t pos;
        struct page *page;
        struct logfs_disk_dentry *dd;

        if (ctx->pos < 0)
                return -EINVAL;

        if (!dir_emit_dots(file, ctx))
                return 0;

        pos = ctx->pos - 2;
        BUG_ON(pos < 0);
        for (;; pos++, ctx->pos++) {
                bool full;
                if (beyond_eof(dir, pos))
                        break;
                if (!logfs_exist_block(dir, pos)) {
                        /* deleted dentry */
                        pos = dir_seek_data(dir, pos);
                        continue;
                }
                page = read_cache_page(dir->i_mapping, pos,
                                (filler_t *)logfs_readpage, NULL);
                if (IS_ERR(page))
                        return PTR_ERR(page);
                dd = kmap(page);
                BUG_ON(dd->namelen == 0);

                full = !dir_emit(ctx, (char *)dd->name,
                                be16_to_cpu(dd->namelen),
                                be64_to_cpu(dd->ino), dd->type);
                kunmap(page);
                page_cache_release(page);
                if (full)
                        break;
        }
        return 0;
}

static void logfs_set_name(struct logfs_disk_dentry *dd, struct qstr *name)
{
        dd->namelen = cpu_to_be16(name->len);
        memcpy(dd->name, name->name, name->len);
}

static struct dentry *logfs_lookup(struct inode *dir, struct dentry *dentry,
                unsigned int flags)
{
        struct page *page;
        struct logfs_disk_dentry *dd;
        pgoff_t index;
        u64 ino = 0;
        struct inode *inode;

        page = logfs_get_dd_page(dir, dentry);
        if (IS_ERR(page))
                return ERR_CAST(page);
        if (!page) {
                d_add(dentry, NULL);
                return NULL;
        }
        index = page->index;
        dd = kmap_atomic(page);
        ino = be64_to_cpu(dd->ino);
        kunmap_atomic(dd);
        page_cache_release(page);

        inode = logfs_iget(dir->i_sb, ino);
        if (IS_ERR(inode))
                printk(KERN_ERR"LogFS: Cannot read inode #%llx for dentry (%lx, %lx)n",
                                ino, dir->i_ino, index);
        return d_splice_alias(inode, dentry);
}

static void grow_dir(struct inode *dir, loff_t index)
{
        index = (index + 1) << dir->i_sb->s_blocksize_bits;
        if (i_size_read(dir) < index)
                i_size_write(dir, index);
}

static int logfs_write_dir(struct inode *dir, struct dentry *dentry,
                struct inode *inode)
{
        struct page *page;
        struct logfs_disk_dentry *dd;
        u32 hash = hash_32(dentry->d_name.name, dentry->d_name.len, 0);
        pgoff_t index;
        int round, err;

        for (round = 0; round < 20; round++) {
                index = hash_index(hash, round);

                if (logfs_exist_block(dir, index))
                        continue;
                page = find_or_create_page(dir->i_mapping, index, GFP_KERNEL);
                if (!page)
                        return -ENOMEM;

                dd = kmap_atomic(page);
                memset(dd, 0, sizeof(*dd));
                dd->ino = cpu_to_be64(inode->i_ino);
                dd->type = logfs_type(inode);
                logfs_set_name(dd, &dentry->d_name);
                kunmap_atomic(dd);

                err = logfs_write_buf(dir, page, WF_LOCK);
                unlock_page(page);
                page_cache_release(page);
                if (!err)
                        grow_dir(dir, index);
                return err;
        }
        /* FIXME: Is there a better return value?  In most cases neither
         * the filesystem nor the directory are full.  But we have had
         * too many collisions for this particular hash and no fallback.
         */
        return -ENOSPC;
}

static int __logfs_create(struct inode *dir, struct dentry *dentry,
                struct inode *inode, const char *dest, long destlen)
{
        struct logfs_super *super = logfs_super(dir->i_sb);
        struct logfs_inode *li = logfs_inode(inode);
        struct logfs_transaction *ta;
        int ret;

        ta = kzalloc(sizeof(*ta), GFP_KERNEL);
        if (!ta) {
                drop_nlink(inode);
                iput(inode);
                return -ENOMEM;
        }

        ta->state = CREATE_1;
        ta->ino = inode->i_ino;
        mutex_lock(&super->s_dirop_mutex);
        logfs_add_transaction(inode, ta);

        if (dest) {
                /* symlink */
                ret = logfs_inode_write(inode, dest, destlen, 0, WF_LOCK, NULL);
                if (!ret)
                        ret = write_inode(inode);
        } else {
                /* creat/mkdir/mknod */
                ret = write_inode(inode);
        }
        if (ret) {
                abort_transaction(inode, ta);
                li->li_flags |= LOGFS_IF_STILLBORN;
                /* FIXME: truncate symlink */
                drop_nlink(inode);
                iput(inode);
                goto out;
        }

        ta->state = CREATE_2;
        logfs_add_transaction(dir, ta);
        ret = logfs_write_dir(dir, dentry, inode);
        /* sync directory */
        if (!ret)
                ret = write_inode(dir);

        if (ret) {
                logfs_del_transaction(dir, ta);
                ta->state = CREATE_2;
                logfs_add_transaction(inode, ta);
                logfs_remove_inode(inode);
                iput(inode);
                goto out;
        }
        d_instantiate(dentry, inode);
out:
        mutex_unlock(&super->s_dirop_mutex);
        return ret;
}

static int logfs_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
{
        struct inode *inode;

        /*
         * FIXME: why do we have to fill in S_IFDIR, while the mode is
         * correct for mknod, creat, etc.?  Smells like the vfs *should*
         * do it for us but for some reason fails to do so.
         */
        inode = logfs_new_inode(dir, S_IFDIR | mode);
        if (IS_ERR(inode))
                return PTR_ERR(inode);

        inode->i_op = &logfs_dir_iops;
        inode->i_fop = &logfs_dir_fops;

        return __logfs_create(dir, dentry, inode, NULL, 0);
}

static int logfs_create(struct inode *dir, struct dentry *dentry, umode_t mode,
                bool excl)
{
        struct inode *inode;

        inode = logfs_new_inode(dir, mode);
        if (IS_ERR(inode))
                return PTR_ERR(inode);

        inode->i_op = &logfs_reg_iops;
        inode->i_fop = &logfs_reg_fops;
        inode->i_mapping->a_ops = &logfs_reg_aops;

        return __logfs_create(dir, dentry, inode, NULL, 0);
}

static int logfs_mknod(struct inode *dir, struct dentry *dentry, umode_t mode,
                dev_t rdev)
{
        struct inode *inode;

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

        inode = logfs_new_inode(dir, mode);
        if (IS_ERR(inode))
                return PTR_ERR(inode);

        init_special_inode(inode, mode, rdev);

        return __logfs_create(dir, dentry, inode, NULL, 0);
}

static int logfs_symlink(struct inode *dir, struct dentry *dentry,
                const char *target)
{
        struct inode *inode;
        size_t destlen = strlen(target) + 1;

        if (destlen > dir->i_sb->s_blocksize)
                return -ENAMETOOLONG;

        inode = logfs_new_inode(dir, S_IFLNK | 0777);
        if (IS_ERR(inode))
                return PTR_ERR(inode);

        inode->i_op = &logfs_symlink_iops;
        inode->i_mapping->a_ops = &logfs_reg_aops;

        return __logfs_create(dir, dentry, inode, target, destlen);
}

static int logfs_link(struct dentry *old_dentry, struct inode *dir,
                struct dentry *dentry)
{
        struct inode *inode = old_dentry->d_inode;

        inode->i_ctime = dir->i_ctime = dir->i_mtime = CURRENT_TIME;
        ihold(inode);
        inc_nlink(inode);
        mark_inode_dirty_sync(inode);

        return __logfs_create(dir, dentry, inode, NULL, 0);
}

static int logfs_get_dd(struct inode *dir, struct dentry *dentry,
                struct logfs_disk_dentry *dd, loff_t *pos)
{
        struct page *page;
        void *map;

        page = logfs_get_dd_page(dir, dentry);
        if (IS_ERR(page))
                return PTR_ERR(page);
        *pos = page->index;
        map = kmap_atomic(page);
        memcpy(dd, map, sizeof(*dd));
        kunmap_atomic(map);
        page_cache_release(page);
        return 0;
}

static int logfs_delete_dd(struct inode *dir, loff_t pos)
{
        /*
         * Getting called with pos somewhere beyond eof is either a goofup
         * within this file or means someone maliciously edited the
         * (crc-protected) journal.
         */
        BUG_ON(beyond_eof(dir, pos));
        dir->i_ctime = dir->i_mtime = CURRENT_TIME;
        log_dir(" Delete dentry (%lx, %llx)\n", dir->i_ino, pos);
        return logfs_delete(dir, pos, NULL);
}

/*
 * Cross-directory rename, target does not exist.  Just a little nasty.
 * Create a new dentry in the target dir, then remove the old dentry,
 * all the while taking care to remember our operation in the journal.
 */
static int logfs_rename_cross(struct inode *old_dir, struct dentry *old_dentry,
                              struct inode *new_dir, struct dentry *new_dentry)
{
        struct logfs_super *super = logfs_super(old_dir->i_sb);
        struct logfs_disk_dentry dd;
        struct logfs_transaction *ta;
        loff_t pos;
        int err;

        /* 1. locate source dd */
        err = logfs_get_dd(old_dir, old_dentry, &dd, &pos);
        if (err)
                return err;

        ta = kzalloc(sizeof(*ta), GFP_KERNEL);
        if (!ta)
                return -ENOMEM;

        ta->state = CROSS_RENAME_1;
        ta->dir = old_dir->i_ino;
        ta->pos = pos;

        /* 2. write target dd */
        mutex_lock(&super->s_dirop_mutex);
        logfs_add_transaction(new_dir, ta);
        err = logfs_write_dir(new_dir, new_dentry, old_dentry->d_inode);
        if (!err)
                err = write_inode(new_dir);

        if (err) {
                super->s_rename_dir = 0;
                super->s_rename_pos = 0;
                abort_transaction(new_dir, ta);
                goto out;
        }

        /* 3. remove source dd */
        ta->state = CROSS_RENAME_2;
        logfs_add_transaction(old_dir, ta);
        err = logfs_delete_dd(old_dir, pos);
        if (!err)
                err = write_inode(old_dir);
        LOGFS_BUG_ON(err, old_dir->i_sb);
out:
        mutex_unlock(&super->s_dirop_mutex);
        return err;
}

static int logfs_replace_inode(struct inode *dir, struct dentry *dentry,
                struct logfs_disk_dentry *dd, struct inode *inode)
{
        loff_t pos;
        int err;

        err = logfs_get_dd(dir, dentry, dd, &pos);
        if (err)
                return err;
        dd->ino = cpu_to_be64(inode->i_ino);
        dd->type = logfs_type(inode);

        err = write_dir(dir, dd, pos);
        if (err)
                return err;
        log_dir("Replace dentry (%lx, %llx) %s -> %llx\n", dir->i_ino, pos,
                        dd->name, be64_to_cpu(dd->ino));
        return write_inode(dir);
}

/* Target dentry exists - the worst case.  We need to attach the source
 * inode to the target dentry, then remove the orphaned target inode and
 * source dentry.
 */
static int logfs_rename_target(struct inode *old_dir, struct dentry *old_dentry,
                               struct inode *new_dir, struct dentry *new_dentry)
{
        struct logfs_super *super = logfs_super(old_dir->i_sb);
        struct inode *old_inode = old_dentry->d_inode;
        struct inode *new_inode = new_dentry->d_inode;
        int isdir = S_ISDIR(old_inode->i_mode);
        struct logfs_disk_dentry dd;
        struct logfs_transaction *ta;
        loff_t pos;
        int err;

        BUG_ON(isdir != S_ISDIR(new_inode->i_mode));
        if (isdir) {
                if (!logfs_empty_dir(new_inode))
                        return -ENOTEMPTY;
        }

        /* 1. locate source dd */
        err = logfs_get_dd(old_dir, old_dentry, &dd, &pos);
        if (err)
                return err;

        ta = kzalloc(sizeof(*ta), GFP_KERNEL);
        if (!ta)
                return -ENOMEM;

        ta->state = TARGET_RENAME_1;
        ta->dir = old_dir->i_ino;
        ta->pos = pos;
        ta->ino = new_inode->i_ino;

        /* 2. attach source inode to target dd */
        mutex_lock(&super->s_dirop_mutex);
        logfs_add_transaction(new_dir, ta);
        err = logfs_replace_inode(new_dir, new_dentry, &dd, old_inode);
        if (err) {
                super->s_rename_dir = 0;
                super->s_rename_pos = 0;
                super->s_victim_ino = 0;
                abort_transaction(new_dir, ta);
                goto out;
        }

        /* 3. remove source dd */
        ta->state = TARGET_RENAME_2;
        logfs_add_transaction(old_dir, ta);
        err = logfs_delete_dd(old_dir, pos);
        if (!err)
                err = write_inode(old_dir);
        LOGFS_BUG_ON(err, old_dir->i_sb);

        /* 4. remove target inode */
        ta->state = TARGET_RENAME_3;
        logfs_add_transaction(new_inode, ta);
        err = logfs_remove_inode(new_inode);

out:
        mutex_unlock(&super->s_dirop_mutex);
        return err;
}

static int logfs_rename(struct inode *old_dir, struct dentry *old_dentry,
                        struct inode *new_dir, struct dentry *new_dentry)
{
        if (new_dentry->d_inode)
                return logfs_rename_target(old_dir, old_dentry,
                                           new_dir, new_dentry);
        return logfs_rename_cross(old_dir, old_dentry, new_dir, new_dentry);
}

/* No locking done here, as this is called before .get_sb() returns. */
int logfs_replay_journal(struct super_block *sb)
{
        struct logfs_super *super = logfs_super(sb);
        struct inode *inode;
        u64 ino, pos;
        int err;

        if (super->s_victim_ino) {
                /* delete victim inode */
                ino = super->s_victim_ino;
                printk(KERN_INFO"LogFS: delete unmapped inode #%llx\n", ino);
                inode = logfs_iget(sb, ino);
                if (IS_ERR(inode))
                        goto fail;

                LOGFS_BUG_ON(i_size_read(inode) > 0, sb);
                super->s_victim_ino = 0;
                err = logfs_remove_inode(inode);
                iput(inode);
                if (err) {
                        super->s_victim_ino = ino;
                        goto fail;
                }
        }
        if (super->s_rename_dir) {
                /* delete old dd from rename */
                ino = super->s_rename_dir;
                pos = super->s_rename_pos;
                printk(KERN_INFO"LogFS: delete unbacked dentry (%llx, %llx)\n",
                                ino, pos);
                inode = logfs_iget(sb, ino);
                if (IS_ERR(inode))
                        goto fail;

                super->s_rename_dir = 0;
                super->s_rename_pos = 0;
                err = logfs_delete_dd(inode, pos);
                iput(inode);
                if (err) {
                        super->s_rename_dir = ino;
                        super->s_rename_pos = pos;
                        goto fail;
                }
        }
        return 0;
fail:
        LOGFS_BUG(sb);
        return -EIO;
}

const struct inode_operations logfs_symlink_iops = {
        .readlink       = generic_readlink,
        .follow_link    = page_follow_link_light,
};

const struct inode_operations logfs_dir_iops = {
        .create         = logfs_create,
        .link           = logfs_link,
        .lookup         = logfs_lookup,
        .mkdir          = logfs_mkdir,
        .mknod          = logfs_mknod,
        .rename         = logfs_rename,
        .rmdir          = logfs_rmdir,
        .symlink        = logfs_symlink,
        .unlink         = logfs_unlink,
};
const struct file_operations logfs_dir_fops = {
        .fsync          = logfs_fsync,
        .unlocked_ioctl = logfs_ioctl,
        .iterate        = logfs_readdir,
        .read           = generic_read_dir,
        .llseek         = default_llseek,
};