can-utils/isobusfs/isobusfs_srv_dh.c

// SPDX-License-Identifier: GPL-2.0-only
// SPDX-FileCopyrightText: 2023 Oleksij Rempel <linux@rempel-privat.de>

#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>

#include "isobusfs_srv.h"
#include "isobusfs_cmn_dh.h"

void isobusfs_srv_set_default_current_dir(struct isobusfs_srv_priv *priv,
					  struct isobusfs_srv_client *client)
{
	snprintf(client->current_dir, ISOBUSFS_SRV_MAX_PATH_LEN, "\\\\%s",
		 priv->default_volume);
}

static const char *isobusfs_srv_get_volume_end(const char *path, size_t path_size)
{
	const char *vol_end = NULL;
	size_t i;

	if (!path || !path_size)
		return NULL;

	if (!(path[0] == '\\' && path[1] == '\\' && path[2] != '\0'))
		return NULL;

	for (i = 2; i < path_size; i++) {
		if (path[i] == '\\' || path[i] == '\0') {
			vol_end = &path[i];
			break;
		}
	}

	if (!vol_end)
		vol_end = &path[i];

	return vol_end;
}

int isobusfs_path_to_linux_path(struct isobusfs_srv_priv *priv,
		const char *isobusfs_path, size_t isobusfs_path_size,
		char *linux_path, size_t linux_path_size)
{
	struct isobusfs_srv_volume *volume = NULL;
	size_t isobusfs_path_pos = 0;
	const char *vol_end;
	char *ptr;
	int i;

	if (!priv || !isobusfs_path || !linux_path || !linux_path_size ||
	    !isobusfs_path_size) {
		pr_err("%s: invalid argument\n", __func__);
		return -EINVAL;
	}

	vol_end = isobusfs_srv_get_volume_end(isobusfs_path, isobusfs_path_size);
	if (!vol_end) {
		pr_err("%s: invalid path %s. Can't find end of volume string\n",
		       __func__, isobusfs_path);
		return -EINVAL;
	}

	/* Search for the volume in the priv->volumes array */
	for (i = 0; i < priv->volume_count; i++) {
		size_t volume_name_len = vol_end - (isobusfs_path + 2);

		if (volume_name_len == strlen(priv->volumes[i].name) &&
			memcmp(priv->volumes[i].name, isobusfs_path + 2,
			       volume_name_len) == 0) {
			volume = &priv->volumes[i];
			break;
		}
	}
	if (!volume) {
		pr_err("%s: invalid path %s. Can't find volume\n",
		       __func__, isobusfs_path);
		return -ENODEV;
	}

	/* Copy the volume's Linux path to the output buffer */
	strncpy(linux_path, volume->path, linux_path_size - 1);
	linux_path[linux_path_size - 1] = '\0';

	isobusfs_path_pos = vol_end - isobusfs_path;
	/* Add a forward slash if path ends after volume name */
	if (*vol_end == '\0' || isobusfs_path_pos == isobusfs_path_size - 1)
		strncat(linux_path, "/",
			linux_path_size - strlen(linux_path) - 1);


	if (isobusfs_path_pos + 3 < isobusfs_path_size && strncmp(vol_end, "\\~\\", 3) == 0) {
		strncat(linux_path, "/", linux_path_size - strlen(linux_path) - 1);
		/* convert tilde to manufacturer-specific directory */
		strncat(linux_path, priv->mfs_dir,
			linux_path_size - strlen(linux_path) - 1);
		vol_end += 2;
	}

	/* Replace backslashes with forward slashes for the rest of the path */
	ptr = linux_path + strlen(linux_path);
	while (vol_end < isobusfs_path + isobusfs_path_size && *vol_end) {
		if (*vol_end == '\\')
			*ptr = '/';
		else
			*ptr = *vol_end;

		ptr++;
		vol_end++;
		if (ptr - linux_path >= linux_path_size) {
			/* Ensure null termination */
			linux_path[linux_path_size - 1] = '\0';
			break;
		}
	}

	return 0;
}

int isobusfs_check_current_dir_access(struct isobusfs_srv_priv *priv,
				      const char *path, size_t path_size)
{
	char linux_path[ISOBUSFS_SRV_MAX_PATH_LEN];
	int ret;

	ret = isobusfs_path_to_linux_path(priv, path, path_size,
					  linux_path, sizeof(linux_path));
	if (ret < 0)
		return ret;

	pr_debug("convert ISOBUS FS path to linux path: %.*s -> %s",
		 path_size, path, linux_path);

	ret = isobusfs_cmn_dh_validate_dir_path(linux_path, false);
	if (ret < 0)
		return ret;

	return 0;
}

/* current directory response function */
static int isobusfs_srv_dh_current_dir_res(struct isobusfs_srv_priv *priv,
					   struct isobusfs_msg *msg)
{
	struct isobusfs_dh_get_cd_req *req =
		(struct isobusfs_dh_get_cd_req *)msg->buf;
	uint8_t error_code = ISOBUSFS_ERR_SUCCESS;
	struct isobusfs_dh_get_cd_res *res;
	struct isobusfs_srv_client *client;
	size_t str_len, buf_size;
	size_t fixed_res_size;
	size_t padding_size = 0;
	int ret;

	client = isobusfs_srv_get_client_by_msg(priv, msg);
	if (!client) {
		pr_warn("client not found");
		return -ENOENT;
	}

	if (client->current_dir[0] == '\0')
		isobusfs_srv_set_default_current_dir(priv, client);

	ret = isobusfs_check_current_dir_access(priv, client->current_dir,
					 sizeof(client->current_dir));
	if (ret < 0) {
		switch (ret) {
		case -ENOENT:
			error_code = ISOBUSFS_ERR_FILE_ORPATH_NOT_FOUND;
		case -ENOMEDIUM:
			error_code = ISOBUSFS_ERR_VOLUME_NOT_INITIALIZED;
		case -ENOMEM:
			error_code = ISOBUSFS_ERR_OUT_OF_MEM;
		default:
			error_code = ISOBUSFS_ERR_OTHER;
		}
	}

	fixed_res_size = sizeof(*res);
	str_len = strlen(client->current_dir) + 1;
	buf_size = fixed_res_size + str_len;

	if (buf_size > ISOBUSFS_MAX_TRANSFER_LENGH) {
		pr_warn("current directory response too long");

		/* Calculate the maximum allowed string length based on the
		 * buffer size
		 */
		str_len = ISOBUSFS_MAX_TRANSFER_LENGH - fixed_res_size;

		/* Update the buffer size accordingly */
		buf_size = fixed_res_size + str_len;

		error_code = ISOBUSFS_ERR_OUT_OF_MEM;

	} else if (buf_size < ISOBUSFS_MIN_TRANSFER_LENGH) {
		/* Update the buffer size accordingly */
		padding_size = ISOBUSFS_MIN_TRANSFER_LENGH - buf_size;
		buf_size = ISOBUSFS_MIN_TRANSFER_LENGH;
	}

	res = malloc(buf_size);
	if (!res) {
		pr_err("failed to allocate memory for current directory response");
		return -ENOMEM;
	}

	res->fs_function =
		isobusfs_cg_function_to_buf(ISOBUSFS_CG_DIRECTORY_HANDLING,
					    ISOBUSFS_DH_F_GET_CURRENT_DIR_RES);
	res->tan = req->tan;
	res->error_code = error_code;
	/* TODO: implement total_space and free_space */
	res->total_space = htole16(0);
	res->free_space = htole16(0);
	res->name_len = htole16(str_len);
	memcpy(res->name, client->current_dir, str_len);

	if (padding_size) {
		/* Fill the rest of the res structure with 0xff */
		memset(((uint8_t *)res) + buf_size - padding_size, 0xff,
		       padding_size);
	}

	/* send to socket */
	ret = isobusfs_srv_sendto(priv, msg, res, buf_size);
	if (ret < 0) {
		pr_warn("can't send current directory response");
		goto free_res;
	}

	pr_debug("> tx: current directory response: %s, total space: %i, free space: %i",
			 client->current_dir, le16toh(res->total_space),
			 le16toh(res->free_space));

free_res:
	free(res);

	return ret;
}

/**
 * isobusfs_is_forbidden_char() - check if the given character is forbidden
 * @ch: character to check
 *
 * Return: true if the character is forbidden, false otherwise
 *
 * The function checks if the given character is forbidden in the ISOBUS FS
 * as defined in ISO 11783-13:2021, section A.2.2.1 Names:
 * To avoid incompatibility between different operating systems, the client
 * shall not create folder/files with names, which only differs in case, and
 * names shall not end with a '.' or include ‘<’, ‘>’, ‘|’ (the latter three
 * may cause issues on FAT32).
 * ....
 * LongNameChar ::= any single character defined by Unicode/ISO/IEC 10646,
 * except 0x00 to 0x1f, 0x7f to 0x9f, ‘\’, ‘*’, ‘?’, ‘/’.
 */
static bool isobusfs_is_forbidden_char(wchar_t ch)
{
	if (ch >= 0x00 && ch <= 0x1f)
		return true;
	if (ch >= 0x7f && ch <= 0x9f)
		return true;
	if (ch == L'*' || ch == L'?' || ch == L'/' ||
		ch == L'<' || ch == L'>' || ch == L'|')
		return true;
	return false;
}

static int isobusfs_validate_path_chars(const char *path, size_t size)
{
	for (size_t i = 0; i < size; ++i) {
		wchar_t ch = path[i];

		if (isobusfs_is_forbidden_char(ch))
			return -EINVAL;
	}
	return 0;
}

static int isobusfs_handle_path_prefix(const char *current_dir,
				       size_t current_dir_len,
				       const char *rel_path,
				       size_t rel_path_size,
				       size_t *rel_path_pos, char *abs_path,
				       size_t abs_path_size,
				       size_t *abs_path_pos)
{
	if (strncmp(rel_path, "~\\", 2) == 0) {
		size_t vol_len;
		const char *vol_end;

		vol_end = isobusfs_srv_get_volume_end(current_dir,
						      current_dir_len);
		if (!vol_end)
			return -EINVAL;

		vol_len = vol_end - current_dir;
		strncpy(abs_path, current_dir, vol_len);
		abs_path[vol_len] = '\\';
		*abs_path_pos = vol_len + 1;
	} else if (strncmp(rel_path, "\\\\", 2) == 0) {
		/* Too many back slashes, drop it. */
		if (rel_path[2] == '\\')
			return -EINVAL;

		strncpy(abs_path, rel_path, 2);
		*abs_path_pos = 2;
		*rel_path_pos = 2;
	} else {
		strncpy(abs_path, current_dir, abs_path_size);
		*abs_path_pos = current_dir_len;
		if (abs_path[*abs_path_pos - 1] != '\\') {
			if (*abs_path_pos < abs_path_size - 1) {
				abs_path[*abs_path_pos] = '\\';
				*abs_path_pos += 1;
			} else {
				return -ENOMEM;
			}
		}
		if (rel_path[*rel_path_pos] == '\\')
			*rel_path_pos += 1;
	}

	return 0;
}

/**
 * is_valid_path_char - Check if the current character is valid in the path
 * @rel_path: The relative path being processed
 * @rel_path_size: The size of the relative path
 * @rel_path_pos: Pointer to the current position in the relative path
 *
 * Checks if the current character at the position in the relative path
 * is not the end of the string, not a null character, and not a backslash.
 *
 * Return: True if the current character is valid, False otherwise.
 */
static bool is_valid_path_char(const char *rel_path, size_t rel_path_size,
			       const size_t *rel_path_pos)
{
	return *rel_path_pos < rel_path_size &&
		   rel_path[*rel_path_pos] != '\0' &&
		   rel_path[*rel_path_pos] != '\\';
}

/**
 * Checks if the specified number of positions ahead in the relative path
 * are either the end of the buffer or a backslash.
 *
 * @param rel_path The relative path being processed.
 * @param rel_path_size The size of the relative path.
 * @param rel_path_pos The current position in the relative path.
 * @param look_ahead The number of positions ahead to check.
 * @return True if the specified positions ahead are the end or a backslash,
 * False otherwise.
 */
static bool is_end_or_backslash(const char *rel_path, size_t rel_path_size,
				const size_t *rel_path_pos, size_t look_ahead)
{
	if (*rel_path_pos + look_ahead >= rel_path_size)
		return true; /* End of buffer */

	return rel_path[*rel_path_pos + look_ahead] == '\\';
}

/**
 * is_path_separator - Check if the current character is a path separator
 * @rel_path: The relative path being processed
 * @rel_path_size: The size of the relative path
 * @rel_path_pos: Pointer to the current position in the relative path
 *
 * Checks if the current character at the position in the relative path
 * is a backslash and the position is within the string size.
 *
 * Return: True if the current character is a backslash, False otherwise.
 */
static bool is_path_separator(const char *rel_path, size_t rel_path_size,
			      const size_t *rel_path_pos)
{
	return *rel_path_pos < rel_path_size && rel_path[*rel_path_pos] == '\\';
}

static bool isobusfs_is_dot_directive(const char *rel_path,
				      size_t rel_path_size,
				      const size_t *rel_path_pos)
{
	if (rel_path[*rel_path_pos] == '.') {
		/* Check for '.' followed by a backslash or at the end of the
		 * string
		 */
		if (is_end_or_backslash(rel_path, rel_path_size,
					rel_path_pos, 1) ||
		    rel_path[*rel_path_pos + 1] == '\0') {
			return true;
		}

		/* Check for '..' followed by a backslash or at the end of the
		 * string
		 */
		if (rel_path[*rel_path_pos + 1] == '.') {
			if (is_end_or_backslash(rel_path, rel_path_size,
						rel_path_pos, 2) ||
				rel_path[*rel_path_pos + 2] == '\0') {
				return true;
			}
		}
	}

	return false;
}

/**
 * isobusfs_handle_single_dot - Processes a single dot directive in a relative
 *				path
 * @rel_path: The relative path being processed
 * @rel_path_size: The size of the relative path
 * @rel_path_pos: Pointer to the current position in the relative path
 *
 * This function checks if the current segment in the relative path is a single
 * dot ('.'). A single dot represents the current directory. If the next
 * character after the dot is either a backslash or the end of the string,
 * the function advances the path position appropriately. The function returns
 * true if it processes a single dot, indicating that the current directory
 * directive was found and handled.
 *
 * Return: True if a single dot directive is detected, False otherwise.
 */
static bool isobusfs_handle_single_dot(const char *rel_path,
				       size_t rel_path_size,
				       size_t *rel_path_pos)
{
	bool is_dot = false;

	if (is_end_or_backslash(rel_path, rel_path_size, rel_path_pos, 1)) {
		*rel_path_pos += 2;
		is_dot = true;
	} else if (rel_path[*rel_path_pos + 1] == '\0') {
		*rel_path_pos += 1;
		is_dot = true;
	}

	return is_dot;
}

/**
 * isobusfs_handle_double_dots - Processes a double dot directive in a relative
 *				 path
 *
 * @rel_path: The relative path being processed
 * @rel_path_size: The size of the relative path
 * @rel_path_pos: Pointer to the current position in the relative path
 * @abs_path: Buffer to store the absolute path being constructed
 * @abs_path_pos: Pointer to the current position in the absolute path buffer
 *
 * This function processes the double dot directive ('..') in a relative path.
 * The double dot represents the parent directory. If the double dot directive
 * is followed by a backslash or is at the end of the string, the function
 * advances the path position accordingly. Additionally, it adjusts the
 * absolute path position to move up one directory in the path hierarchy. The
 * function ensures that it does not go beyond the root of the absolute path
 * while moving up the directory hierarchy.
 */
static void isobusfs_handle_double_dots(const char *rel_path,
					size_t rel_path_size,
					size_t *rel_path_pos, char *abs_path,
					size_t *abs_path_pos)
{
	/* Move the relative path position forward after handling '..' */
	if (is_end_or_backslash(rel_path, rel_path_size, rel_path_pos, 2))
		*rel_path_pos += 3;
	else if (rel_path[*rel_path_pos + 2] == '\0')
		*rel_path_pos += 2;

	/* Move the absolute path position backward to simulate moving up a
	 * directory
	 */
	if (*abs_path_pos > 2 && abs_path[*abs_path_pos - 1] == '\\')
		*abs_path_pos -= 1;

	while (*abs_path_pos > 2 && abs_path[*abs_path_pos - 1] != '\\')
		*abs_path_pos -= 1;
}

/**
 * isobusfs_handle_dot_directive - Processes '.' and '..' directives in a path
 * @rel_path: The relative path being processed
 * @rel_path_size: The size of the relative path
 * @rel_path_pos: Pointer to the current position in the relative path
 * @abs_path: Buffer to store the absolute path being constructed
 * @abs_path_pos: Pointer to the current position in the absolute path buffer
 *
 * This function processes the dot directives found in a relative path. It
 * handles both single dot ('.') and double dot ('..') directives. A single dot
 * represents the current directory, while a double dot represents moving up to
 * the parent directory.
 */
static void isobusfs_handle_dot_directive(const char *rel_path,
					  size_t rel_path_size,
					  size_t *rel_path_pos, char *abs_path,
					  size_t *abs_path_pos)
{
	if (rel_path[*rel_path_pos] == '.') {
		bool is_dot = isobusfs_handle_single_dot(rel_path, rel_path_size,
						rel_path_pos);

		if (!is_dot && rel_path[*rel_path_pos + 1] == '.') {
			isobusfs_handle_double_dots(rel_path, rel_path_size,
					   rel_path_pos, abs_path,
					   abs_path_pos);
		}
	}

	/* Skip additional backslashes after '.' or '..' */
	while (is_path_separator(rel_path, rel_path_size, rel_path_pos))
		*rel_path_pos += 1;
}

/**
 * isobusfs_process_path_segment - Processes normal path segments
 * @rel_path: The relative path being processed
 * @rel_path_size: The size of the relative path
 * @rel_path_pos: Pointer to the current position in the relative path
 * @abs_path: The buffer to store the absolute path
 * @abs_path_size: The size of the absolute path buffer
 * @abs_path_pos: Pointer to the position in the absolute path buffer
 *
 * This function processes normal segments of a relative path, copying them
 * into the absolute path buffer. It handles each character until it encounters
 * a path separator or reaches the end of the relative path. If a path separator
 * is found, it adds a single backslash to the absolute path. The function
 * ensures that the buffer limits are respected to prevent buffer overflows.
 *
 * Return: 0 on successful processing of the segment, -ENOMEM if the absolute
 * path buffer runs out of space.
 */
static int isobusfs_process_path_segment(const char *rel_path,
					 size_t rel_path_size,
					 size_t *rel_path_pos, char *abs_path,
					 size_t abs_path_size,
					 size_t *abs_path_pos)
{
	/*  Process the current character from the relative path */
	abs_path[*abs_path_pos] = rel_path[*rel_path_pos];
	*abs_path_pos += 1;
	*rel_path_pos += 1;

	/* Continue processing until a path separator or end of the string is
	 * reached
	 */
	while (is_valid_path_char(rel_path, rel_path_size, rel_path_pos)) {
		if (*abs_path_pos >= abs_path_size - 1)
			return -ENOMEM;

		abs_path[*abs_path_pos] = rel_path[*rel_path_pos];
		*rel_path_pos += 1;
		*abs_path_pos += 1;
	}
	/* Add a single backslash if next character is a backslash */
	if (is_path_separator(rel_path, rel_path_size, rel_path_pos)) {
		*rel_path_pos += 1;
		if (*abs_path_pos < abs_path_size - 1) {
			abs_path[*abs_path_pos] = '\\';
			*abs_path_pos += 1;
		}
	}

	return 0;
}

static int isobusfs_handle_relative_path(const char *rel_path,
					 size_t rel_path_size,
					 size_t *rel_path_pos, char *abs_path,
					 size_t abs_path_size,
					 size_t *abs_path_pos)
{
	int ret;

	if (*abs_path_pos >= abs_path_size - 1)
		return -ENOMEM;

	/* Check for '.' or '..' followed by a backslash or at the end of the
	 * string
	 */
	if (isobusfs_is_dot_directive(rel_path, rel_path_size, rel_path_pos)) {
		isobusfs_handle_dot_directive(rel_path, rel_path_size,
					       rel_path_pos, abs_path,
					       abs_path_pos);
	} else {
		/* Process normally for filenames or directories */
		ret = isobusfs_process_path_segment(rel_path, rel_path_size,
						    rel_path_pos, abs_path,
						    abs_path_size,
						    abs_path_pos);
		if (ret)
			return ret;
	}

	return 0;
}

int isobusfs_convert_relative_to_absolute(struct isobusfs_srv_priv *priv,
					  const char *current_dir,
					  const char *rel_path,
					  size_t rel_path_size, char *abs_path,
					  size_t abs_path_size)
{
	size_t abs_path_pos = 0;
	size_t rel_path_pos = 0;
	size_t current_dir_len;
	int ret;

	if (!current_dir || !rel_path || !abs_path || !rel_path_size ||
	    !abs_path_size)
		return -EINVAL;

	ret = isobusfs_validate_path_chars(rel_path, rel_path_size);
	if (ret != 0)
		return ret;

	current_dir_len = strlen(current_dir);
	if (current_dir_len >= abs_path_size)
		return -ENOMEM;
	if (current_dir_len == 0)
		return -EINVAL;

	ret = isobusfs_handle_path_prefix(current_dir, current_dir_len,
					  rel_path, rel_path_size,
					  &rel_path_pos, abs_path,
					  abs_path_size, &abs_path_pos);
	if (ret)
		return ret;

	while (rel_path_pos < rel_path_size && rel_path[rel_path_pos] != '\0') {
		ret = isobusfs_handle_relative_path(rel_path, rel_path_size,
						    &rel_path_pos, abs_path,
						    abs_path_size,
						    &abs_path_pos);
		if (ret)
			return ret;
	}

	abs_path[abs_path_pos] = '\0';

	return 0;
}

/* change current directory response function */
static int isobusfs_srv_dh_ccd_res(struct isobusfs_srv_priv *priv,
				   struct isobusfs_msg *msg)
{
	struct isobusfs_dh_ccd_req *req =
		(struct isobusfs_dh_ccd_req *)msg->buf;
	uint8_t error_code = ISOBUSFS_ERR_SUCCESS;
	struct isobusfs_srv_client *client;
	struct isobusfs_dh_ccd_res res;
	size_t abs_path_len;
	char *abs_path;
	int ret;

	/*
	 * We assime, the relative path stored in res->name is not longer
	 * than absolue path
	 */
	if (req->name_len > ISOBUSFS_SRV_MAX_PATH_LEN) {
		pr_warn("path too long");
		return -EINVAL;
	}

	client = isobusfs_srv_get_client_by_msg(priv, msg);
	if (!client) {
		pr_warn("client not found");
		return -ENOENT;
	}

	abs_path_len = ISOBUSFS_SRV_MAX_PATH_LEN;
	abs_path = malloc(abs_path_len);
	if (!abs_path) {
		pr_warn("failed to allocate memory");
		return -ENOMEM;
	}

	pr_debug("< rx change current directory request from client 0x%2x: %.*s. Current directory: %s",
		 client->addr, req->name_len, req->name, client->current_dir);
	/* Normalize provided string and convert it to absolute ISOBUS FS path */
	ret = isobusfs_convert_relative_to_absolute(priv, client->current_dir,
						    (char *)req->name, req->name_len,
						    abs_path, abs_path_len);
	if (ret < 0)
		goto process_error;

	pr_debug("converted relative to absolute ISOBUS FS internal path: %s", abs_path);
	ret = isobusfs_check_current_dir_access(priv, abs_path, abs_path_len);
process_error:
	if (ret < 0) {
		/* linux_error_to_isobusfs_error() can't distinguish between
		 * -EINVAL vor SRC and DST, so we have to do it manually.
		 */
		if (ret == -EINVAL)
			error_code = ISOBUSFS_ERR_INVALID_DST_NAME;
		else
			error_code = linux_error_to_isobusfs_error(ret);
	} else {
		/* change current directory */
		strncpy(client->current_dir, abs_path, ISOBUSFS_SRV_MAX_PATH_LEN);
	}

	res.fs_function =
		isobusfs_cg_function_to_buf(ISOBUSFS_CG_DIRECTORY_HANDLING,
					    ISOBUSFS_DH_F_CHANGE_CURRENT_DIR_RES);
	res.tan = req->tan;
	res.error_code = error_code;
	memset(&res.reserved[0], 0xff, sizeof(res.reserved));

	/* send to socket */
	ret = isobusfs_srv_sendto(priv, msg, &res, sizeof(res));
	if (ret < 0) {
		pr_warn("can't send current directory response");
		goto free_abs_path;
	}

	pr_debug("> tx: ccd response. Error code: %d", error_code);
free_abs_path:
	free(abs_path);

	return ret;
}

/* current directory response function */
/* Command group: directory handling */
int isobusfs_srv_rx_cg_dh(struct isobusfs_srv_priv *priv,
			  struct isobusfs_msg *msg)
{
	int func = isobusfs_buf_to_function(msg->buf);
	int ret = 0;

	switch (func) {
	case ISOBUSFS_DH_F_GET_CURRENT_DIR_REQ:
		return isobusfs_srv_dh_current_dir_res(priv, msg);
	case ISOBUSFS_DH_F_CHANGE_CURRENT_DIR_REQ:
		return isobusfs_srv_dh_ccd_res(priv, msg);
	default:
		goto not_supported;
	}

	return ret;

not_supported:
	isobusfs_srv_send_error(priv, msg, ISOBUSFS_ERR_FUNC_NOT_SUPPORTED);

	pr_warn("%s: unsupported function: %i", __func__, func);

	/* Not a critical error */
	return 0;
}