Merge 61eb881dc9 into 95aae6bf83

isobusfs/isobusfs_cli.c

@@ -671,6 +671,10 @@ int main(int argc, char *argv[])
 
 	while (1) {
 		ret = isobusfs_cli_process_events_and_tasks(priv);
+		if (ret == ISOBUSFS_CLI_RET_EXIT) {
+			ret = 0;
+			break;
+		}
 		if (ret)
 			break;
 	}

isobusfs/isobusfs_cli.h

@@ -13,6 +13,9 @@
 #define ISOBUSFS_CLI_MAX_EPOLL_EVENTS		10
 #define ISOBUSFS_CLI_DEFAULT_WAIT_TIMEOUT_MS	1000 /* ms */
 
+/* internal return codes, not errno values */
+#define ISOBUSFS_CLI_RET_EXIT			1
+
 enum isobusfs_cli_state {
 	ISOBUSFS_CLI_STATE_CONNECTING,
 	ISOBUSFS_CLI_STATE_IDLE,

isobusfs/isobusfs_cli_int.c

@@ -16,6 +16,12 @@
 #define MAX_COMMAND_LENGTH 256
 
 #define MAX_DISPLAY_FILENAME_LENGTH 100
+/*
+ * ISO 11783-13:2021 B.21 minimal directory entry payload size in bytes:
+ * 1 (name length) + 1 (min name byte) + 1 (attributes) +
+ * 2 (date) + 2 (time) + 4 (size).
+ */
+#define ISOBUSFS_MIN_DIR_ENTRY_SIZE (1 + 1 + 1 + 2 + 2 + 4)
 
 struct command_mapping {
 	const char *command;
@@ -66,8 +72,8 @@ static int cmd_help(struct isobusfs_priv *priv, const char *options)
 static int cmd_exit(struct isobusfs_priv *priv, const char *options)
 {
 	pr_int("exit interactive mode\n");
-	/* Return -EINTR to indicate the program should exit */
+
-	return -EINTR;
+	return ISOBUSFS_CLI_RET_EXIT;
 }
 
 static int cmd_dmesg(struct isobusfs_priv *priv, const char *options)
@@ -510,8 +516,12 @@ isobusfs_cli_ls_handle_open_dir_sent(struct isobusfs_priv *priv,
 
 	ctx->handle = res->handle;
 
+	ctx->offset = 0;
+	ctx->entry_count = 0;
+
 	ret = isobusfs_cli_send_and_register_fa_sf_event(priv, ctx->handle,
-							 0, ctx->entry_count,
+							 ISOBUSFS_FA_SEEK_SET,
+							 ctx->offset,
 							 cb, ctx);
 	if (ret)
 		pr_int("Failed to send seek file request: %i\n", ret);
@@ -530,7 +540,7 @@ isobusfs_cli_ls_handle_seek_dir_sent(struct isobusfs_priv *priv,
 {
 	isobusfs_event_callback cb = isobusfs_cli_ls_event_callback;
 	struct isobusfs_fa_seekf_res *res =
-		(struct isobusfs_fa_seekf_res *)msg;
+		(struct isobusfs_fa_seekf_res *)msg->buf;
 	uint16_t count;
 	int ret;
 
@@ -543,8 +553,10 @@ isobusfs_cli_ls_handle_seek_dir_sent(struct isobusfs_priv *priv,
 		goto error;
 	}
 
-	/* set max possible number fitting in to 16bits */
+	/* ISO 11783-13:2021 C.3.5.2: count is number of directory entries. */
-	count = UINT16_MAX;
+	count = ISOBUSFS_MAX_DATA_LENGH / ISOBUSFS_MIN_DIR_ENTRY_SIZE;
+	if (!count)
+		count = 1;
 	ctx->request_count = count;
 
 	ret = isobusfs_cli_send_and_register_fa_rf_event(priv, ctx->handle,
@@ -616,8 +628,8 @@ static bool isobusfs_cli_extract_directory_entry(const uint8_t *buffer,
 						 uint16_t *file_time,
 						 uint32_t *file_size)
 {
+	size_t entry_total_len, copy_len;
 	uint8_t filename_length;
-	size_t entry_total_len;
 
 	if (*pos + 2 > buffer_length) {
 		pr_int("Error: Incomplete data in buffer\n");
@@ -633,8 +645,14 @@ static bool isobusfs_cli_extract_directory_entry(const uint8_t *buffer,
 	}
 
 	(*pos)++;
-	strncpy(filename, (const char *)buffer + *pos, filename_length);
+
-	filename[filename_length] = '\0';
+	if (filename_length > ISOBUSFS_MAX_DIR_ENTRY_NAME_LENGTH)
+		copy_len = ISOBUSFS_MAX_DIR_ENTRY_NAME_LENGTH;
+	else
+		copy_len = filename_length;
+
+	strncpy(filename, (const char *)buffer + *pos, copy_len);
+	filename[copy_len] = '\0';
 	*pos += filename_length;
 	if (filename_length > MAX_DISPLAY_FILENAME_LENGTH) {
 		/* Truncate the filename and replace the last character
@@ -688,15 +706,17 @@ isobusfs_cli_print_directory_entry(struct isobusfs_cli_ls_context *ctx,
 static void
 isobusfs_cli_print_directory_entries(struct isobusfs_cli_ls_context *ctx,
 				     const uint8_t *buffer,
-				     size_t buffer_length)
+				     size_t buffer_length,
+				     uint16_t max_entries)
 {
 	char filename[ISOBUSFS_MAX_DIR_ENTRY_NAME_LENGTH + 1];
 	uint16_t file_date, file_time;
 	uint32_t file_size;
 	uint8_t attributes;
 	size_t pos = 0;
+	uint16_t entries = 0;
 
-	while (pos < buffer_length) {
+	while (pos < buffer_length && entries < max_entries) {
 		if (!isobusfs_cli_extract_directory_entry(buffer, buffer_length,
 							  &pos, filename,
 							  &attributes,
@@ -709,6 +729,7 @@ isobusfs_cli_print_directory_entries(struct isobusfs_cli_ls_context *ctx,
 						   file_date, file_time,
 						   file_size);
 		ctx->entry_count++;
+		entries++;
 	}
 }
 
@@ -721,26 +742,42 @@ isobusfs_cli_ls_handle_read_dir_sent(struct isobusfs_priv *priv,
 		(struct isobusfs_read_file_response *)msg->buf;
 	size_t buffer_length = msg->len - sizeof(*res);
 	isobusfs_event_callback cb;
+	size_t entries_before;
+	size_t entries_in_message;
 	uint16_t count;
 	int ret;
 
 	pr_debug("< rx: Read File Response. Error code: %i", res->error_code);
+
 	if (isobusfs_cli_int_is_error(priv, 0, res->error_code, res->tan))
 		goto error;
 
 	count = le16toh(res->count);
-	if (count && count != buffer_length) {
+	if (count && buffer_length) {
-		pr_int("Buffer length mismatch: %u != %zu\n", count,
+		entries_before = ctx->entry_count;
-		       buffer_length);
+		isobusfs_cli_print_directory_entries(ctx, res->data,
-		goto error;
+						     buffer_length, count);
+		entries_in_message = ctx->entry_count - entries_before;
+	} else {
+		entries_in_message = 0;
 	}
 
-	if (count)
+	if (count != entries_in_message) {
-		isobusfs_cli_print_directory_entries(ctx, res->data,
+		pr_warn("Directory entry count mismatch: server sent %u, parsed %zu\n",
-						     buffer_length);
+			count, entries_in_message);
+		/* Continue processing if we parsed at least some entries.
+		 * Strict validation would reject valid responses if parsing
+		 * fails partway through due to corruption.
+		 */
+		if (entries_in_message == 0 && count > 0) {
+			pr_int("Error: Failed to parse any directory entries\n");
+			goto error;
+		}
+	}
 
 	cb = isobusfs_cli_ls_event_callback;
-	if (count) {
+
+	if (res->error_code == ISOBUSFS_ERR_END_OF_FILE) {
 		ret = isobusfs_cli_send_and_register_fa_cf_event(priv,
 								 ctx->handle,
 								 cb, ctx);
@@ -750,21 +787,31 @@ isobusfs_cli_ls_handle_read_dir_sent(struct isobusfs_priv *priv,
 		}
 
 		ctx->state = ISOBUSFS_CLI_LS_STATE_CLOSE_DIR_SENT;
-	} else {
+		return;
-		ctx->offset = ctx->entry_count;
-		ret = isobusfs_cli_send_and_register_fa_sf_event(priv,
-								 ctx->handle, 0,
-								 ctx->offset,
-								 cb, ctx);
-		if (ret)
-			pr_int("Failed to send seek file request: %i\n", ret);
-
-		ctx->state = ISOBUSFS_CLI_LS_STATE_SEEK_DIR_SENT;
 	}
 
+	if (!count) {
+		pr_int("Error: zero-length read without EOF\n");
+		goto error;
+	}
+
+	/*
+	 * Directory seek offset is entry index, not byte offset.
+	 * Server side seek rewinds and skips "offset" entries.
+	 */
+	ctx->offset = ctx->entry_count;
+
+	ret = isobusfs_cli_send_and_register_fa_sf_event(priv,
+							 ctx->handle, 0,
+							 ctx->offset,
+							 cb, ctx);
+	if (ret)
+		pr_int("Failed to send seek file request: %i\n", ret);
+
+	ctx->state = ISOBUSFS_CLI_LS_STATE_SEEK_DIR_SENT;
+
 	return;
 error:
-
 	ctx->state = ISOBUSFS_CLI_LS_STATE_ERROR;
 }
 

isobusfs/isobusfs_cli_selftests.c

@@ -603,23 +603,24 @@ struct isobusfs_cli_test_rf_path {
 	uint8_t flags;
 	uint32_t offset;
 	uint32_t read_size;
+	uint32_t expected_size;
 	bool expect_pass;
 };
 
 static struct isobusfs_cli_test_rf_path test_rf_patterns[] = {
 	/* expected result \\vol1\dir1\dir2\ */
-	{ "\\\\vol1\\dir1\\dir2\\file1k", 0, 0, 0, true },
+	{ "\\\\vol1\\dir1\\dir2\\file1k", 0, 0, 0, 0, true },
-	{ "\\\\vol1\\dir1\\dir2\\file1k", 0, 0, 1, true },
+	{ "\\\\vol1\\dir1\\dir2\\file1k", 0, 0, 1, 1, true },
-	{ "\\\\vol1\\dir1\\dir2\\file1k", 0, 1, 1, true },
+	{ "\\\\vol1\\dir1\\dir2\\file1k", 0, 1, 1, 1, true },
-	{ "\\\\vol1\\dir1\\dir2\\file1k", 0, 2, 1, true },
+	{ "\\\\vol1\\dir1\\dir2\\file1k", 0, 2, 1, 1, true },
-	{ "\\\\vol1\\dir1\\dir2\\file1k", 0, 3, 1, true },
+	{ "\\\\vol1\\dir1\\dir2\\file1k", 0, 3, 1, 1, true },
-	{ "\\\\vol1\\dir1\\dir2\\file1m", 0, 0, 8, true },
+	{ "\\\\vol1\\dir1\\dir2\\file1m", 0, 0, 8, 8, true },
-	{ "\\\\vol1\\dir1\\dir2\\file1m", 0, 0, 8 * 100, true },
+	{ "\\\\vol1\\dir1\\dir2\\file1m", 0, 0, 8 * 100, 8 * 100, true },
-	{ "\\\\vol1\\dir1\\dir2\\file1m", 0, 100, 8 * 100, true },
+	{ "\\\\vol1\\dir1\\dir2\\file1m", 0, 100, 8 * 100, 8 * 100, true },
-	{ "\\\\vol1\\dir1\\dir2\\file1m", 0, 0, ISOBUSFS_MAX_DATA_LENGH, true },
+	{ "\\\\vol1\\dir1\\dir2\\file1m", 0, 0, ISOBUSFS_MAX_DATA_LENGH, ISOBUSFS_MAX_DATA_LENGH, true },
-	{ "\\\\vol1\\dir1\\dir2\\file1m", 0, 0, (ISOBUSFS_MAX_DATA_LENGH & ~3) + 16, true },
+	{ "\\\\vol1\\dir1\\dir2\\file1m", 0, 0, (ISOBUSFS_MAX_DATA_LENGH & ~3) + 16, (ISOBUSFS_MAX_DATA_LENGH & ~3) + 16, true },
-	{ "\\\\vol1\\dir1\\dir2\\file1m", 0, 0, ISOBUSFS_MAX_DATA_LENGH + 1, true },
+	{ "\\\\vol1\\dir1\\dir2\\file1m", 0, 0, ISOBUSFS_MAX_DATA_LENGH + 1, ISOBUSFS_MAX_DATA_LENGH + 1, true },
-	{ "\\\\vol1\\dir1\\dir2\\file1m", 0, 0, -1, true },
+	{ "\\\\vol1\\dir1\\dir2\\file1m", 0, 0, UINT32_MAX, 1024 * 1024, true },
 };
 
 size_t current_rf_pattern_test;
@@ -678,7 +679,8 @@ static int isobusfs_cli_test_rf_req(struct isobusfs_priv *priv, bool *complete)
 		&test_rf_patterns[current_rf_pattern_test];
 	uint32_t actual_sum, expected_sum;
 	struct timespec current_time;
-	ssize_t remaining_size, read_size;
+	int64_t remaining_size;
+	ssize_t read_size;
 	int ret;
 
 	clock_gettime(CLOCK_MONOTONIC, &current_time);
@@ -801,16 +803,23 @@ static int isobusfs_cli_test_rf_req(struct isobusfs_priv *priv, bool *complete)
 		free(priv->read_data);
 		priv->read_data = NULL;
 
-		remaining_size = (tp->offset + tp->read_size) -
+		remaining_size = ((int64_t)tp->offset + tp->read_size) -
-				(priv->read_offset + priv->read_data_len);
+				((int64_t)priv->read_offset + priv->read_data_len);
-		pr_debug("remaining_size: %zd, read_offset: %zu, read_data_len: %zu, test read size: %zu, test offset %zu",
+		pr_debug("remaining_size: %lld, read_offset: %zu, read_data_len: %zu, test read size: %u, test offset %u",
-			 remaining_size, priv->read_offset, priv->read_data_len,
+			 (long long)remaining_size, priv->read_offset, priv->read_data_len,
 			 tp->read_size, tp->offset);
 		if (remaining_size < 0) {
 			pr_err("pattern test failed: %s. Read size is too big",
 			       tp->path_name);
 			ret = -EINVAL;
 			goto test_fail;
+		} else if (remaining_size == 0) {
+			if (tp->read_size > tp->expected_size) {
+				pr_err("read test failed: %s. Server returned more data than expected file size (%u > %u)",
+				       tp->path_name, tp->read_size, tp->expected_size);
+				ret = -EINVAL;
+				goto test_fail;
+			}
 		} else if (remaining_size > 0 && priv->read_data_len != 0) {
 			priv->read_offset += priv->read_data_len;
 
@@ -825,11 +834,20 @@ static int isobusfs_cli_test_rf_req(struct isobusfs_priv *priv, bool *complete)
 				goto test_fail;
 			test_start_time = current_time;
 			break;
-		} else if (remaining_size > 0 && priv->read_data_len == 0 && tp->expect_pass) {
+		} else if (remaining_size > 0 && priv->read_data_len == 0) {
-			pr_err("read test failed: %s. Read size is zero, but expected more data: %zd",
+			if (tp->read_size > tp->expected_size &&
-			       tp->path_name, remaining_size);
+			    tp->read_size - remaining_size == tp->expected_size) {
-			ret = -EINVAL;
+				/* this is acceptable case when read size
-			goto test_fail;
+				 * is larger than actual file size
+				 */
+				pr_info("read test passed: %s. Reached end of file as expected.",
+					tp->path_name);
+			} else {
+				pr_err("read test failed: %s. Server returned zero bytes, but expected more data: %lld",
+				       tp->path_name, (long long)remaining_size);
+				ret = -EINVAL;
+				goto test_fail;
+			}
 		}
 
 		/* fall troth */

isobusfs/isobusfs_srv_fa.c

@@ -495,15 +495,119 @@ static int check_access_with_base(const char *base_dir,
 	return access(full_path, mode);
 }
 
+/*
+ * ISO 11783-13:2021 B.21 and B.15:
+ * Filters directory entries that can be returned in a Read File response
+ * for directory handles while collecting the attributes and name length.
+ */
+/**
+ * isobusfs_srv_dir_entry_visible() - Filter visible directory entries.
+ * @handle: Directory handle for access checks.
+ * @entry: Directory entry to inspect.
+ * @file_stat: Stat buffer to fill for the entry.
+ * @entry_name_len: Returns entry name length on success.
+ * @attributes: Returns computed attributes on success.
+ *
+ * ISO 11783-13:2021 B.21 and B.15 define the directory entry layout and
+ * attributes. This helper skips entries that are not readable or too long
+ * and returns attributes for the entry that will be serialized.
+ *
+ * Return: true when the entry should be emitted, false otherwise.
+ */
+static bool isobusfs_srv_dir_entry_visible(struct isobusfs_srv_handles *handle,
+					   const struct dirent *entry,
+					   struct stat *file_stat,
+					   size_t *entry_name_len,
+					   uint8_t *attributes)
+{
+	if (check_access_with_base(handle->path, entry->d_name, R_OK) != 0)
+		return false;
+
+	if (fstatat(handle->fd, entry->d_name, file_stat, 0) < 0)
+		return false;
+
+	*entry_name_len = strlen(entry->d_name);
+	if (*entry_name_len > ISOBUSFS_MAX_DIR_ENTRY_NAME_LENGTH)
+		return false;
+
+	if (S_ISDIR(file_stat->st_mode))
+		*attributes |= ISOBUSFS_ATTR_DIRECTORY;
+	if (check_access_with_base(handle->path, entry->d_name, W_OK) != 0)
+		*attributes |= ISOBUSFS_ATTR_READ_ONLY;
+
+	return true;
+}
+
+/*
+ * ISO 11783-13:2021 C.3.4.2 and C.3.5.2:
+ * Directory offsets/counts are in entries, so advance the directory stream
+ * by visible entries only and report EOF if the entry offset is past the end.
+ */
+/**
+ * isobusfs_srv_dir_skip_entries() - Advance directory stream by entries.
+ * @handle: Directory handle to reposition.
+ * @offset: Entry offset to seek to.
+ *
+ * ISO 11783-13:2021 C.3.4.2 and C.3.5.2 state directory offsets/counts are in
+ * entries. This helper advances by visible entries only.
+ *
+ * Return: ISOBUSFS_ERR_SUCCESS or a protocol error code.
+ */
+static int isobusfs_srv_dir_skip_entries(struct isobusfs_srv_handles *handle,
+					 int32_t offset)
+{
+	struct dirent *entry;
+	int32_t skipped = 0;
+
+	rewinddir(handle->dir);
+
+	while (skipped < offset && (entry = readdir(handle->dir)) != NULL) {
+		struct stat file_stat;
+		size_t entry_name_len = 0;
+		uint8_t attributes = 0;
+
+		if (!isobusfs_srv_dir_entry_visible(handle, entry, &file_stat,
+						    &entry_name_len,
+						    &attributes))
+			continue;
+
+		skipped++;
+	}
+
+	if (offset > 0 && skipped < offset)
+		return ISOBUSFS_ERR_END_OF_FILE;
+
+	return ISOBUSFS_ERR_SUCCESS;
+}
+
+/**
+ * isobusfs_srv_read_directory() - Read directory entries into a response buffer.
+ * @handle: Directory handle to read.
+ * @buffer: Output buffer for directory entries.
+ * @max_bytes: Maximum payload bytes allowed in the response.
+ * @max_entries: Maximum number of entries to return.
+ * @readed_size: Returns payload size in bytes.
+ * @entries_read: Returns number of entries serialized.
+ *
+ * ISO 11783-13:2021 C.3.5.2: directory Count is entry based. This function
+ * encodes up to @max_entries entries while respecting @max_bytes.
+ *
+ * Return: ISOBUSFS_ERR_SUCCESS or a protocol error code.
+ */
 static int isobusfs_srv_read_directory(struct isobusfs_srv_handles *handle,
-				       uint8_t *buffer, size_t count,
+				       uint8_t *buffer, size_t max_bytes,
-				       ssize_t *readed_size)
+				       uint16_t max_entries,
+				       ssize_t *readed_size,
+				       uint16_t *entries_read)
 {
 	DIR *dir = handle->dir;
 	struct dirent *entry;
 	size_t pos = 0;
+	int ret;
 
 	/*
+	 * ISO 11783-13:2021 C.3.5.2:
+	 * Directory offsets are entry indices, not byte positions.
 	 * Position the directory stream to the previously stored offset (handle->dir_pos).
 	 *
 	 * Handling Changes in Directory Contents:
@@ -519,13 +623,18 @@ static int isobusfs_srv_read_directory(struct isobusfs_srv_handles *handle,
 	 *   either returning an error or restarting from the beginning of the directory, depending
 	 *   on the application's requirements.
 	 */
-	for (int i = 0; i < handle->dir_pos &&
+	if (handle->dir_pos < 0) {
-	     (entry = readdir(dir)) != NULL; i++) {
+		pr_err("Directory handle in invalid state (pos=%d)\n",
-		/* Iterating to the desired position */
+		       handle->dir_pos);
+		return ISOBUSFS_ERR_INVALID_HANDLE;
 	}
 
+	ret = isobusfs_srv_dir_skip_entries(handle, handle->dir_pos);
+	if (ret != ISOBUSFS_ERR_SUCCESS)
+		return ret;
+
 	/*
-	 * Directory Entry Layout:
+	 * Directory Entry Layout (ISO 11783-13:2021 B.21):
 	 * This loop reads directory entries and encodes them into a buffer.
 	 * Each entry in the buffer follows the format specified in ISO 11783-13:2021.
 	 *
@@ -550,26 +659,23 @@ static int isobusfs_srv_read_directory(struct isobusfs_srv_handles *handle,
 	 * The handle->dir_pos is incremented after processing each entry, marking
 	 * the current position in the directory stream for subsequent reads.
 	 */
-	while ((entry = readdir(dir)) != NULL) {
+	*entries_read = 0;
+	while ((entry = readdir(dir)) != NULL &&
+	       (*entries_read) < max_entries) {
 		size_t entry_name_len, entry_total_len;
 		__le16 file_date, file_time;
-		uint8_t attributes = 0;
 		struct stat file_stat;
+		uint8_t attributes = 0;
 		__le32 size;
 
-		if (check_access_with_base(handle->path, entry->d_name, R_OK) != 0)
+		if (!isobusfs_srv_dir_entry_visible(handle, entry, &file_stat,
-			continue; /* Skip this entry if it's not readable */
+						    &entry_name_len,
-
+						    &attributes))
-		if (fstatat(handle->fd, entry->d_name, &file_stat, 0) < 0)
-			continue; /* Skip this entry on error */
-
-		entry_name_len = strlen(entry->d_name);
-		if (entry_name_len > ISOBUSFS_MAX_DIR_ENTRY_NAME_LENGTH)
 			continue;
 
 		entry_total_len = 1 + entry_name_len + 1 + 2 + 2 + 4;
 
-		if (pos + entry_total_len > count)
+		if (pos + entry_total_len > max_bytes)
 			break;
 
 		buffer[pos++] = (uint8_t)entry_name_len;
@@ -577,10 +683,6 @@ static int isobusfs_srv_read_directory(struct isobusfs_srv_handles *handle,
 		memcpy(buffer + pos, entry->d_name, entry_name_len);
 		pos += entry_name_len;
 
-		if (S_ISDIR(file_stat.st_mode))
-			attributes |= ISOBUSFS_ATTR_DIRECTORY;
-		if (check_access_with_base(handle->path, entry->d_name, W_OK) != 0)
-			attributes |= ISOBUSFS_ATTR_READ_ONLY;
 		buffer[pos++] = attributes;
 
 		file_date = htole16(convert_to_file_date(file_stat.st_mtime));
@@ -594,9 +696,11 @@ static int isobusfs_srv_read_directory(struct isobusfs_srv_handles *handle,
 		size = htole32(file_stat.st_size);
 		memcpy(buffer + pos, &size, sizeof(size));
 		pos += sizeof(size);
+		(*entries_read)++;
 	}
 
 	*readed_size = pos;
+	handle->dir_pos += *entries_read;
 	return 0;
 }
 
@@ -609,13 +713,18 @@ static int isobusfs_srv_fa_rf_req(struct isobusfs_srv_priv *priv,
 	struct isobusfs_srv_client *client;
 	struct isobusfs_fa_readf_req *req;
 	ssize_t readed_size = 0;
+	uint16_t entries_read = 0;
 	uint8_t error_code = 0;
 	ssize_t send_size;
+	bool res_allocated = false;
+	size_t max_bytes = 0;
+	uint16_t count = 0;
 	int ret = 0;
-	int count;
+	bool is_dir = false;
 
 	req = (struct isobusfs_fa_readf_req *)msg->buf;
 	count = le16toh(req->count);
+	res = (struct isobusfs_read_file_response *)&res_fail[0];
 
 	pr_debug("< rx: Read File Request. tan: %d, handle: %d, count: %d",
 		 req->tan, req->handle, count);
@@ -627,17 +736,6 @@ static int isobusfs_srv_fa_rf_req(struct isobusfs_srv_priv *priv,
 	 * TODO: currently we are not able to detect support transport mode,
 	 * so ETP is assumed.
 	 */
-	if (count > ISOBUSFS_MAX_DATA_LENGH)
-		count = ISOBUSFS_MAX_DATA_LENGH;
-
-	res = malloc(sizeof(*res) + count);
-	if (!res) {
-		pr_warn("failed to allocate memory");
-		res = (struct isobusfs_read_file_response *)&res_fail[0];
-		error_code = ISOBUSFS_ERR_OUT_OF_MEM;
-		goto send_response;
-	}
-
 	client = isobusfs_srv_get_client_by_msg(priv, msg);
 	if (!client) {
 		pr_warn("client not found");
@@ -649,12 +747,33 @@ static int isobusfs_srv_fa_rf_req(struct isobusfs_srv_priv *priv,
 	if (!handle) {
 		pr_warn("failed to find file with handle: %x", req->handle);
 		error_code = ISOBUSFS_ERR_FILE_ORPATH_NOT_FOUND;
+		goto send_response;
 	}
 
 	/* Determine whether to read a file or a directory */
 	if (handle->dir) {
-		ret = isobusfs_srv_read_directory(handle, res->data, count,
+		/* ISO 11783-13:2021 C.3.5.2: count is entry count for directories. */
-						  &readed_size);
+		is_dir = true;
+		max_bytes = ISOBUSFS_MAX_DATA_LENGH;
+	} else {
+		if (count > ISOBUSFS_MAX_DATA_LENGH)
+			count = ISOBUSFS_MAX_DATA_LENGH;
+		max_bytes = count;
+	}
+
+	res = malloc(sizeof(*res) + max_bytes);
+	if (!res) {
+		pr_warn("failed to allocate memory");
+		res = (struct isobusfs_read_file_response *)&res_fail[0];
+		error_code = ISOBUSFS_ERR_OUT_OF_MEM;
+		goto send_response;
+	}
+	res_allocated = true;
+
+	if (is_dir) {
+		ret = isobusfs_srv_read_directory(handle, res->data, max_bytes,
+						  count, &readed_size,
+						  &entries_read);
 	} else {
 		ret = isobusfs_srv_read_file(handle, res->data, count,
 					     &readed_size);
@@ -663,7 +782,10 @@ static int isobusfs_srv_fa_rf_req(struct isobusfs_srv_priv *priv,
 	if (ret < 0) {
 		error_code = ret;
 		readed_size = 0;
-	} else if (count != 0 && readed_size == 0) {
+		entries_read = 0;
+	} else if (count != 0 &&
+		   ((is_dir && entries_read == 0) ||
+		    (!is_dir && readed_size == 0))) {
 		error_code = ISOBUSFS_ERR_END_OF_FILE;
 	}
 
@@ -673,7 +795,10 @@ send_response:
 					    ISOBUSFS_FA_F_READ_FILE_RES);
 	res->tan = req->tan;
 	res->error_code = error_code;
-	res->count = htole16(readed_size);
+	if (is_dir)
+		res->count = htole16(entries_read);
+	else
+		res->count = htole16(readed_size);
 
 	send_size = sizeof(*res) + readed_size;
 	if (send_size < ISOBUSFS_MIN_TRANSFER_LENGH)
@@ -690,7 +815,8 @@ send_response:
 		 error_code, isobusfs_error_to_str(error_code), readed_size);
 
 free_res:
-	free(res);
+	if (res_allocated)
+		free(res);
 	return ret;
 }
 
@@ -754,19 +880,56 @@ static int isobusfs_srv_seek(struct isobusfs_srv_priv *priv,
 	return ISOBUSFS_ERR_SUCCESS;
 }
 
+/**
+ * isobusfs_srv_seek_directory() - Seek a directory by entry index.
+ * @handle: Directory handle to seek.
+ * @offset: Entry index to seek to.
+ *
+ * ISO 11783-13:2021 C.3.4.2 defines directory offsets as entry indices.
+ *
+ * Return: ISOBUSFS_ERR_SUCCESS or a protocol error code.
+ */
 static int isobusfs_srv_seek_directory(struct isobusfs_srv_handles *handle,
 				       int32_t offset)
 {
-	DIR *dir = fdopendir(handle->fd);
+	int32_t current_pos = handle->dir_pos;
+	int ret;
 
-	if (!dir)
+	if (!handle->dir)
 		return ISOBUSFS_ERR_OTHER;
 
-	rewinddir(dir);
+	/* Check if handle is in valid state */
+	if (current_pos < 0) {
+		pr_err("Cannot seek directory in invalid state (pos=%d)\n",
+		       current_pos);
+		return ISOBUSFS_ERR_INVALID_HANDLE;
+	}
 
-	for (int32_t i = 0; i < offset; i++) {
+	/* Validate requested offset */
-		if (readdir(dir) == NULL)
+	if (offset < 0) {
-			return ISOBUSFS_ERR_END_OF_FILE;
+		pr_err("Invalid seek offset: %d\n", offset);
+		return ISOBUSFS_ERR_INVALID_REQUESTED_LENGHT;
+	}
+
+	/*
+	 * ISO 11783-13:2021 C.3.4.2:
+	 * Directory offsets are entry indices. If we fail to seek, restore
+	 * the previous entry position since the position shall not change on error.
+	 */
+	ret = isobusfs_srv_dir_skip_entries(handle, offset);
+	if (ret != ISOBUSFS_ERR_SUCCESS) {
+		int restore_ret;
+
+		restore_ret = isobusfs_srv_dir_skip_entries(handle, current_pos);
+		if (restore_ret != ISOBUSFS_ERR_SUCCESS) {
+			pr_warn("Failed to restore directory position after seek failure: %d -> %d",
+				current_pos, restore_ret);
+			/* Directory stream is now in undefined state.
+			 * Mark position as invalid.
+			 */
+			handle->dir_pos = -1;
+		}
+		return ret;
 	}
 
 	handle->dir_pos = offset;