source: mainline/uspace/srv/fs/ext4fs/ext4fs_ops.c@ 36d2c6f

/*
 * Copyright (c) 2011 Frantisek Princ
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - 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.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/** @addtogroup fs
 * @{
 */ 

/**
 * @file        ext4fs_ops.c
 * @brief       VFS operations for EXT4 filesystem.
 */

#include <errno.h>
#include <fibril_synch.h>
#include <libext4.h>
#include <libfs.h>
#include <macros.h>
#include <malloc.h>
#include <adt/hash_table.h>
#include <ipc/loc.h>
#include "ext4fs.h"
#include "../../vfs/vfs.h"

#define EXT4FS_NODE(node)       ((node) ? (ext4fs_node_t *) (node)->data : NULL)

#define OPEN_NODES_KEYS 2
#define OPEN_NODES_DEV_HANDLE_KEY 0
#define OPEN_NODES_INODE_KEY 1
#define OPEN_NODES_BUCKETS 256

typedef struct ext4fs_instance {
        link_t link;
        service_id_t service_id;
        ext4_filesystem_t *filesystem;
        unsigned int open_nodes_count;
} ext4fs_instance_t;

typedef struct ext4fs_node {
        ext4fs_instance_t *instance;
        ext4_inode_ref_t *inode_ref;
        fs_node_t *fs_node;
        link_t link;
        unsigned int references;
} ext4fs_node_t;

/*
 * Forward declarations of auxiliary functions
 */

static int ext4fs_read_directory(ipc_callid_t, aoff64_t, size_t,
    ext4fs_instance_t *, ext4_inode_ref_t *, size_t *);
static int ext4fs_read_file(ipc_callid_t, aoff64_t, size_t, ext4fs_instance_t *,
    ext4_inode_ref_t *, size_t *);
static bool ext4fs_is_dots(const uint8_t *, size_t);
static int ext4fs_instance_get(service_id_t, ext4fs_instance_t **);
static int ext4fs_node_get_core(fs_node_t **, ext4fs_instance_t *, fs_index_t);
static int ext4fs_node_put_core(ext4fs_node_t *);

/*
 * Forward declarations of EXT4 libfs operations.
 */
static int ext4fs_root_get(fs_node_t **, service_id_t);
static int ext4fs_match(fs_node_t **, fs_node_t *, const char *);
static int ext4fs_node_get(fs_node_t **, service_id_t, fs_index_t);
static int ext4fs_node_open(fs_node_t *);
static int ext4fs_node_put(fs_node_t *);
static int ext4fs_create_node(fs_node_t **, service_id_t, int);
static int ext4fs_destroy_node(fs_node_t *);
static int ext4fs_link(fs_node_t *, fs_node_t *, const char *);
static int ext4fs_unlink(fs_node_t *, fs_node_t *, const char *);
static int ext4fs_has_children(bool *, fs_node_t *);
static fs_index_t ext4fs_index_get(fs_node_t *);
static aoff64_t ext4fs_size_get(fs_node_t *);
static unsigned ext4fs_lnkcnt_get(fs_node_t *);
static bool ext4fs_is_directory(fs_node_t *);
static bool ext4fs_is_file(fs_node_t *node);
static service_id_t ext4fs_service_get(fs_node_t *node);

/*
 * Static variables
 */
static LIST_INITIALIZE(instance_list);
static FIBRIL_MUTEX_INITIALIZE(instance_list_mutex);
static hash_table_t open_nodes;
static FIBRIL_MUTEX_INITIALIZE(open_nodes_lock);

/* Hash table interface for open nodes hash table */
static hash_index_t open_nodes_hash(unsigned long key[])
{
        /* TODO: This is very simple and probably can be improved */
        return key[OPEN_NODES_INODE_KEY] % OPEN_NODES_BUCKETS;
}

static int open_nodes_compare(unsigned long key[], hash_count_t keys,
    link_t *item)
{
        ext4fs_node_t *enode = hash_table_get_instance(item, ext4fs_node_t, link);
        assert(keys > 0);
        if (enode->instance->service_id !=
            ((service_id_t) key[OPEN_NODES_DEV_HANDLE_KEY])) {
                return false;
        }
        if (keys == 1) {
                return true;
        }
        assert(keys == 2);
        return (enode->inode_ref->index == key[OPEN_NODES_INODE_KEY]);
}

static void open_nodes_remove_cb(link_t *link)
{
        /* We don't use remove callback for this hash table */
}

static hash_table_operations_t open_nodes_ops = {
        .hash = open_nodes_hash,
        .compare = open_nodes_compare,
        .remove_callback = open_nodes_remove_cb,
};


int ext4fs_global_init(void)
{
        if (!hash_table_create(&open_nodes, OPEN_NODES_BUCKETS,
            OPEN_NODES_KEYS, &open_nodes_ops)) {
                return ENOMEM;
        }
        return EOK;
}


int ext4fs_global_fini(void)
{
        hash_table_destroy(&open_nodes);
        return EOK;
}


/*
 * EXT4 libfs operations.
 */

int ext4fs_instance_get(service_id_t service_id, ext4fs_instance_t **inst)
{
        ext4fs_instance_t *tmp;

        fibril_mutex_lock(&instance_list_mutex);

        if (list_empty(&instance_list)) {
                fibril_mutex_unlock(&instance_list_mutex);
                return EINVAL;
        }

        list_foreach(instance_list, link) {
                tmp = list_get_instance(link, ext4fs_instance_t, link);

                if (tmp->service_id == service_id) {
                        *inst = tmp;
                        fibril_mutex_unlock(&instance_list_mutex);
                        return EOK;
                }
        }

        fibril_mutex_unlock(&instance_list_mutex);
        return EINVAL;
}


int ext4fs_root_get(fs_node_t **rfn, service_id_t service_id)
{
        return ext4fs_node_get(rfn, service_id, EXT4_INODE_ROOT_INDEX);
}


int ext4fs_match(fs_node_t **rfn, fs_node_t *pfn, const char *component)
{
        ext4fs_node_t *eparent = EXT4FS_NODE(pfn);
        ext4_filesystem_t *fs;
        ext4_directory_iterator_t it;
        int rc;
        size_t name_size;
        size_t component_size;
        bool found = false;
        uint32_t inode;

        fs = eparent->instance->filesystem;

        if (!ext4_inode_is_type(fs->superblock, eparent->inode_ref->inode,
            EXT4_INODE_MODE_DIRECTORY)) {
                return ENOTDIR;
        }

        /* Find length of component in bytes
         * TODO: check for library function call that does this
         */
        component_size = 0;
        while (*(component+component_size) != 0) {
                component_size++;
        }

        // TODO check super block COMPAT FEATURES
        if (ext4_inode_has_flag(eparent->inode_ref->inode, EXT4_INODE_FLAG_INDEX)) {

                rc = ext4_directory_dx_find_entry(&it, fs, eparent->inode_ref, component_size, component);

                // Index isn't corrupted
                if (rc != EXT4_ERR_BAD_DX_DIR) {

                        // TODO check return value
                        if (rc != EOK) {
                                return rc;
                        }

                        inode = ext4_directory_entry_ll_get_inode(it.current);

                        rc = ext4fs_node_get_core(rfn, eparent->instance, inode);
                        ext4_directory_iterator_fini(&it);
                        return rc;
                }

        }

        rc = ext4_directory_iterator_init(&it, fs, eparent->inode_ref, 0);
        if (rc != EOK) {
                return rc;
        }

        while (it.current != NULL) {
                inode = ext4_directory_entry_ll_get_inode(it.current);

                /* ignore empty directory entries */
                if (inode != 0) {
                        name_size = ext4_directory_entry_ll_get_name_length(fs->superblock,
                                it.current);

                        if (name_size == component_size && bcmp(component, &it.current->name,
                                    name_size) == 0) {
                                rc = ext4fs_node_get_core(rfn, eparent->instance,
                                        inode);
                                if (rc != EOK) {
                                        ext4_directory_iterator_fini(&it);
                                        return rc;
                                }
                                found = true;
                                break;
                        }
                }

                rc = ext4_directory_iterator_next(&it);
                if (rc != EOK) {
                        ext4_directory_iterator_fini(&it);
                        return rc;
                }
        }

        ext4_directory_iterator_fini(&it);

        if (!found) {
                return ENOENT;
        }

        return EOK;
}


int ext4fs_node_get(fs_node_t **rfn, service_id_t service_id, fs_index_t index)
{
        ext4fs_instance_t *inst = NULL;
        int rc;

        rc = ext4fs_instance_get(service_id, &inst);
        if (rc != EOK) {
                return rc;
        }

        return ext4fs_node_get_core(rfn, inst, index);
}


int ext4fs_node_get_core(fs_node_t **rfn, ext4fs_instance_t *inst,
                fs_index_t index)
{
        int rc;
        fs_node_t *node = NULL;
        ext4fs_node_t *enode = NULL;

        ext4_inode_ref_t *inode_ref = NULL;

        fibril_mutex_lock(&open_nodes_lock);

        /* Check if the node is not already open */
        unsigned long key[] = {
                [OPEN_NODES_DEV_HANDLE_KEY] = inst->service_id,
                [OPEN_NODES_INODE_KEY] = index,
        };
        link_t *already_open = hash_table_find(&open_nodes, key);

        if (already_open) {
                enode = hash_table_get_instance(already_open, ext4fs_node_t, link);
                *rfn = enode->fs_node;
                enode->references++;

                fibril_mutex_unlock(&open_nodes_lock);
                return EOK;
        }

        enode = malloc(sizeof(ext4fs_node_t));
        if (enode == NULL) {
                fibril_mutex_unlock(&open_nodes_lock);
                return ENOMEM;
        }

        node = malloc(sizeof(fs_node_t));
        if (node == NULL) {
                free(enode);
                fibril_mutex_unlock(&open_nodes_lock);
                return ENOMEM;
        }
        fs_node_initialize(node);

        rc = ext4_filesystem_get_inode_ref(inst->filesystem, index, &inode_ref);
        if (rc != EOK) {
                free(enode);
                free(node);
                fibril_mutex_unlock(&open_nodes_lock);
                return rc;
        }

        enode->inode_ref = inode_ref;
        enode->instance = inst;
        enode->references = 1;
        enode->fs_node = node;
        link_initialize(&enode->link);

        node->data = enode;
        *rfn = node;

        hash_table_insert(&open_nodes, key, &enode->link);
        inst->open_nodes_count++;

        fibril_mutex_unlock(&open_nodes_lock);

        return EOK;
}


int ext4fs_node_put_core(ext4fs_node_t *enode)
{
        int rc;
        unsigned long key[] = {
                [OPEN_NODES_DEV_HANDLE_KEY] = enode->instance->service_id,
                [OPEN_NODES_INODE_KEY] = enode->inode_ref->index,
        };

        hash_table_remove(&open_nodes, key, OPEN_NODES_KEYS);
        assert(enode->instance->open_nodes_count > 0);
        enode->instance->open_nodes_count--;

        rc = ext4_filesystem_put_inode_ref(enode->inode_ref);
        if (rc != EOK) {
                return rc;
        }

        free(enode->fs_node);
        free(enode);

        return EOK;
}


int ext4fs_node_open(fs_node_t *fn)
{
        // TODO stateless operation
        return EOK;
}

int ext4fs_node_put(fs_node_t *fn)
{
        int rc;
        ext4fs_node_t *enode = EXT4FS_NODE(fn);

        fibril_mutex_lock(&open_nodes_lock);

        assert(enode->references > 0);
        enode->references--;
        if (enode->references == 0) {
                rc = ext4fs_node_put_core(enode);
                if (rc != EOK) {
                        fibril_mutex_unlock(&open_nodes_lock);
                        return rc;
                }
        }

        fibril_mutex_unlock(&open_nodes_lock);

        return EOK;
}


int ext4fs_create_node(fs_node_t **rfn, service_id_t service_id, int flags)
{
        EXT4FS_DBG("not supported");

        // TODO
        return ENOTSUP;
}


int ext4fs_destroy_node(fs_node_t *fn)
{
        EXT4FS_DBG("not supported");

        // TODO
        return ENOTSUP;
}


int ext4fs_link(fs_node_t *pfn, fs_node_t *cfn, const char *name)
{
        EXT4FS_DBG("not supported");

        // TODO
        return ENOTSUP;
}


int ext4fs_unlink(fs_node_t *pfn, fs_node_t *cfn, const char *nm)
{
        EXT4FS_DBG("not supported");

        // TODO
        return ENOTSUP;
}


int ext4fs_has_children(bool *has_children, fs_node_t *fn)
{
        ext4fs_node_t *enode = EXT4FS_NODE(fn);
        ext4_directory_iterator_t it;
        ext4_filesystem_t *fs;
        int rc;
        bool found = false;
        size_t name_size;

        fs = enode->instance->filesystem;

        if (!ext4_inode_is_type(fs->superblock, enode->inode_ref->inode,
            EXT4_INODE_MODE_DIRECTORY)) {
                *has_children = false;
                return EOK;
        }

        rc = ext4_directory_iterator_init(&it, fs, enode->inode_ref, 0);
        if (rc != EOK) {
                return rc;
        }

        /* Find a non-empty directory entry */
        while (it.current != NULL) {
                if (it.current->inode != 0) {
                        name_size = ext4_directory_entry_ll_get_name_length(fs->superblock,
                                it.current);
                        if (!ext4fs_is_dots(it.current->name, name_size)) {
                                found = true;
                                break;
                        }
                }

                rc = ext4_directory_iterator_next(&it);
                if (rc != EOK) {
                        ext4_directory_iterator_fini(&it);
                        return rc;
                }
        }

        rc = ext4_directory_iterator_fini(&it);
        if (rc != EOK) {
                return rc;
        }

        *has_children = found;

        return EOK;
}


fs_index_t ext4fs_index_get(fs_node_t *fn)
{
        ext4fs_node_t *enode = EXT4FS_NODE(fn);
        return enode->inode_ref->index;
}


aoff64_t ext4fs_size_get(fs_node_t *fn)
{
        ext4fs_node_t *enode = EXT4FS_NODE(fn);
        aoff64_t size = ext4_inode_get_size(enode->instance->filesystem->superblock,
            enode->inode_ref->inode);
        return size;
}


unsigned ext4fs_lnkcnt_get(fs_node_t *fn)
{
        ext4fs_node_t *enode = EXT4FS_NODE(fn);
        unsigned count = ext4_inode_get_links_count(enode->inode_ref->inode);
        return count;
}


bool ext4fs_is_directory(fs_node_t *fn)
{
        ext4fs_node_t *enode = EXT4FS_NODE(fn);
        bool is_dir = ext4_inode_is_type(enode->instance->filesystem->superblock,
            enode->inode_ref->inode, EXT4_INODE_MODE_DIRECTORY);
        return is_dir;
}


bool ext4fs_is_file(fs_node_t *fn)
{
        ext4fs_node_t *enode = EXT4FS_NODE(fn);
        bool is_file = ext4_inode_is_type(enode->instance->filesystem->superblock,
            enode->inode_ref->inode, EXT4_INODE_MODE_FILE);
        return is_file;
}


service_id_t ext4fs_service_get(fs_node_t *fn)
{
        ext4fs_node_t *enode = EXT4FS_NODE(fn);
        return enode->instance->service_id;
}

/*
 * libfs operations.
 */
libfs_ops_t ext4fs_libfs_ops = {
        .root_get = ext4fs_root_get,
        .match = ext4fs_match,
        .node_get = ext4fs_node_get,
        .node_open = ext4fs_node_open,
        .node_put = ext4fs_node_put,
        .create = ext4fs_create_node,
        .destroy = ext4fs_destroy_node,
        .link = ext4fs_link,
        .unlink = ext4fs_unlink,
        .has_children = ext4fs_has_children,
        .index_get = ext4fs_index_get,
        .size_get = ext4fs_size_get,
        .lnkcnt_get = ext4fs_lnkcnt_get,
        .is_directory = ext4fs_is_directory,
        .is_file = ext4fs_is_file,
        .service_get = ext4fs_service_get
};


/*
 * VFS operations.
 */

static int ext4fs_mounted(service_id_t service_id, const char *opts,
   fs_index_t *index, aoff64_t *size, unsigned *lnkcnt)
{
        int rc;
        ext4_filesystem_t *fs;
        ext4fs_instance_t *inst;
        bool read_only;

        /* Allocate libext4 filesystem structure */
        fs = (ext4_filesystem_t *) malloc(sizeof(ext4_filesystem_t));
        if (fs == NULL) {
                return ENOMEM;
        }

        /* Allocate instance structure */
        inst = (ext4fs_instance_t *) malloc(sizeof(ext4fs_instance_t));
        if (inst == NULL) {
                free(fs);
                return ENOMEM;
        }

        /* Initialize the filesystem */
        rc = ext4_filesystem_init(fs, service_id);
        if (rc != EOK) {
                free(fs);
                free(inst);
                return rc;
        }

        /* Do some sanity checking */
        rc = ext4_filesystem_check_sanity(fs);
        if (rc != EOK) {
                ext4_filesystem_fini(fs);
                free(fs);
                free(inst);
                return rc;
        }

        /* Check flags */
        rc = ext4_filesystem_check_features(fs, &read_only);
        if (rc != EOK) {
                ext4_filesystem_fini(fs);
                free(fs);
                free(inst);
                return rc;
        }

        /* Initialize instance */
        link_initialize(&inst->link);
        inst->service_id = service_id;
        inst->filesystem = fs;
        inst->open_nodes_count = 0;

        /* Read root node */
        fs_node_t *root_node;
        rc = ext4fs_node_get_core(&root_node, inst, EXT4_INODE_ROOT_INDEX);
        if (rc != EOK) {
                ext4_filesystem_fini(fs);
                free(fs);
                free(inst);
                return rc;
        }
        ext4fs_node_t *enode = EXT4FS_NODE(root_node);

        /* Add instance to the list */
        fibril_mutex_lock(&instance_list_mutex);
        list_append(&inst->link, &instance_list);
        fibril_mutex_unlock(&instance_list_mutex);

        *index = EXT4_INODE_ROOT_INDEX;
        *size = 0;
        *lnkcnt = ext4_inode_get_links_count(enode->inode_ref->inode);

        ext4fs_node_put(root_node);

        return EOK;
}


static int ext4fs_unmounted(service_id_t service_id)
{
        int rc;
        ext4fs_instance_t *inst;

        rc = ext4fs_instance_get(service_id, &inst);

        if (rc != EOK) {
                return rc;
        }

        fibril_mutex_lock(&open_nodes_lock);

        if (inst->open_nodes_count != 0) {
                fibril_mutex_unlock(&open_nodes_lock);
                return EBUSY;
        }

        /* Remove the instance from the list */
        fibril_mutex_lock(&instance_list_mutex);
        list_remove(&inst->link);
        fibril_mutex_unlock(&instance_list_mutex);

        fibril_mutex_unlock(&open_nodes_lock);

        ext4_filesystem_fini(inst->filesystem);

        return EOK;
}


static int
ext4fs_read(service_id_t service_id, fs_index_t index, aoff64_t pos,
    size_t *rbytes)
{
        ext4fs_instance_t *inst;
        ext4_inode_ref_t *inode_ref;
        int rc;

        /*
         * Receive the read request.
         */
        ipc_callid_t callid;
        size_t size;
        if (!async_data_read_receive(&callid, &size)) {
                async_answer_0(callid, EINVAL);
                return EINVAL;
        }

        rc = ext4fs_instance_get(service_id, &inst);
        if (rc != EOK) {
                async_answer_0(callid, rc);
                return rc;
        }

        rc = ext4_filesystem_get_inode_ref(inst->filesystem, index, &inode_ref);
        if (rc != EOK) {
                async_answer_0(callid, rc);
                return rc;
        }

        if (ext4_inode_is_type(inst->filesystem->superblock, inode_ref->inode,
                        EXT4_INODE_MODE_FILE)) {
                rc = ext4fs_read_file(callid, pos, size, inst, inode_ref,
                                rbytes);
        } else if (ext4_inode_is_type(inst->filesystem->superblock,
                        inode_ref->inode, EXT4_INODE_MODE_DIRECTORY)) {
                rc = ext4fs_read_directory(callid, pos, size, inst, inode_ref,
                                rbytes);
        } else {
                /* Other inode types not supported */
                async_answer_0(callid, ENOTSUP);
                rc = ENOTSUP;
        }

        ext4_filesystem_put_inode_ref(inode_ref);

        return rc;
}

bool ext4fs_is_dots(const uint8_t *name, size_t name_size)
{
        if (name_size == 1 && name[0] == '.') {
                return true;
        }

        if (name_size == 2 && name[0] == '.' && name[1] == '.') {
                return true;
        }

        return false;
}

int ext4fs_read_directory(ipc_callid_t callid, aoff64_t pos, size_t size,
    ext4fs_instance_t *inst, ext4_inode_ref_t *inode_ref, size_t *rbytes)
{

        ext4_directory_iterator_t it;
        aoff64_t next;
        uint8_t *buf;
        size_t name_size;
        int rc;
        bool found = false;

        rc = ext4_directory_iterator_init(&it, inst->filesystem, inode_ref, pos);
        if (rc != EOK) {
                async_answer_0(callid, rc);
                return rc;
        }

        /* Find next interesting directory entry.
         * We want to skip . and .. entries
         * as these are not used in HelenOS
         */
        while (it.current != NULL) {

                if (it.current->inode == 0) {
                        goto skip;
                }

                name_size = ext4_directory_entry_ll_get_name_length(
                    inst->filesystem->superblock, it.current);

                /* skip . and .. */
                if (ext4fs_is_dots(it.current->name, name_size)) {
                        goto skip;
                }

                /* The on-disk entry does not contain \0 at the end
                 * end of entry name, so we copy it to new buffer
                 * and add the \0 at the end
                 */
                buf = malloc(name_size+1);
                if (buf == NULL) {
                        ext4_directory_iterator_fini(&it);
                        async_answer_0(callid, ENOMEM);
                        return ENOMEM;
                }
                memcpy(buf, &it.current->name, name_size);
                *(buf + name_size) = 0;
                found = true;
                (void) async_data_read_finalize(callid, buf, name_size + 1);
                free(buf);
                break;

skip:
                rc = ext4_directory_iterator_next(&it);
                if (rc != EOK) {
                        ext4_directory_iterator_fini(&it);
                        async_answer_0(callid, rc);
                        return rc;
                }
        }

        if (found) {
                rc = ext4_directory_iterator_next(&it);
                if (rc != EOK) {
                        return rc;
                }
                next = it.current_offset;
        }

        rc = ext4_directory_iterator_fini(&it);
        if (rc != EOK) {
                return rc;
        }

        if (found) {
                *rbytes = next - pos;
                return EOK;
        } else {
                async_answer_0(callid, ENOENT);
                return ENOENT;
        }
}

int ext4fs_read_file(ipc_callid_t callid, aoff64_t pos, size_t size,
    ext4fs_instance_t *inst, ext4_inode_ref_t *inode_ref, size_t *rbytes)
{
        int rc;
        uint32_t block_size;
        aoff64_t file_block;
        uint64_t file_size;
        uint32_t fs_block;
        size_t offset_in_block;
        size_t bytes;
        block_t *block;
        uint8_t *buffer;

        file_size = ext4_inode_get_size(inst->filesystem->superblock,
                inode_ref->inode);

        if (pos >= file_size) {
                /* Read 0 bytes successfully */
                async_data_read_finalize(callid, NULL, 0);
                *rbytes = 0;
                return EOK;
        }

        /* For now, we only read data from one block at a time */
        block_size = ext4_superblock_get_block_size(inst->filesystem->superblock);
        file_block = pos / block_size;
        offset_in_block = pos % block_size;
        bytes = min(block_size - offset_in_block, size);

        /* Handle end of file */
        if (pos + bytes > file_size) {
                bytes = file_size - pos;
        }

        /* Get the real block number */
        rc = ext4_filesystem_get_inode_data_block_index(inst->filesystem,
                inode_ref->inode, file_block, &fs_block);
        if (rc != EOK) {
                async_answer_0(callid, rc);
                return rc;
        }

        /* Check for sparse file
         * If ext2_filesystem_get_inode_data_block_index returned
         * fs_block == 0, it means that the given block is not allocated for the
         * file and we need to return a buffer of zeros
         */
        if (fs_block == 0) {
                buffer = malloc(bytes);
                if (buffer == NULL) {
                        async_answer_0(callid, ENOMEM);
                        return ENOMEM;
                }

                memset(buffer, 0, bytes);

                async_data_read_finalize(callid, buffer, bytes);
                *rbytes = bytes;

                free(buffer);

                return EOK;
        }

        /* Usual case - we need to read a block from device */
        rc = block_get(&block, inst->service_id, fs_block, BLOCK_FLAGS_NONE);
        if (rc != EOK) {
                async_answer_0(callid, rc);
                return rc;
        }

        assert(offset_in_block + bytes <= block_size);
        async_data_read_finalize(callid, block->data + offset_in_block, bytes);

        rc = block_put(block);
        if (rc != EOK) {
                return rc;
        }

        *rbytes = bytes;
        return EOK;
}

static int
ext4fs_write(service_id_t service_id, fs_index_t index, aoff64_t pos,
    size_t *wbytes, aoff64_t *nsize)
{
        EXT4FS_DBG("not supported");

        // TODO
        return ENOTSUP;
}


static int
ext4fs_truncate(service_id_t service_id, fs_index_t index, aoff64_t size)
{
        EXT4FS_DBG("not supported");

        // TODO
        return ENOTSUP;
}


static int ext4fs_close(service_id_t service_id, fs_index_t index)
{
        // TODO
        return EOK;
}


static int ext4fs_destroy(service_id_t service_id, fs_index_t index)
{
        EXT4FS_DBG("not supported");

        //TODO
        return ENOTSUP;
}


static int ext4fs_sync(service_id_t service_id, fs_index_t index)
{
        EXT4FS_DBG("not supported");

        // TODO
        return ENOTSUP;
}

vfs_out_ops_t ext4fs_ops = {
        .mounted = ext4fs_mounted,
        .unmounted = ext4fs_unmounted,
        .read = ext4fs_read,
        .write = ext4fs_write,
        .truncate = ext4fs_truncate,
        .close = ext4fs_close,
        .destroy = ext4fs_destroy,
        .sync = ext4fs_sync,
};

/**
 * @}
 */