Introduce a utility function for moving to the next dirent in read_dir.

This takes care of making sure the dirent buffer is properly aligned,
which it needs to be on some platforms (SPARC, ARM, etc.)

Change-Id: I9a6352b1e654c090a200770d51f96511ee024a99

headers/private/file_systems/fs_ops_support.h

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2022, Haiku, Inc. All rights reserved.
+ * Distributed under the terms of the MIT License.
+ */
+#ifndef FS_OPS_SUPPORT_H
+#define FS_OPS_SUPPORT_H
+
+#ifndef FS_SHELL
+#	include <kernel.h>
+#	include <kernel/debug.h>
+#	include <dirent.h>
+#else
+#	include "fssh_kernel_priv.h"
+#endif
+
+
+static struct dirent*
+next_dirent(struct dirent* dirent, size_t nameLength, size_t& bufferRemaining)
+{
+	const size_t reclen = offsetof(struct dirent, d_name) + nameLength + 1;
+	ASSERT(reclen <= bufferRemaining);
+	dirent->d_reclen = reclen;
+
+	const size_t roundedReclen = ROUNDUP(reclen, alignof(struct dirent));
+	if (roundedReclen >= bufferRemaining) {
+		bufferRemaining -= reclen;
+		return NULL;
+	}
+	dirent->d_reclen = roundedReclen;
+	bufferRemaining -= roundedReclen;
+
+	return (struct dirent*)((uint8*)dirent + roundedReclen);
+}
+
+
+#endif	// FS_OPS_SUPPORT_H

src/add-ons/kernel/file_systems/bfs/kernel_interface.cpp

@@ -19,6 +19,8 @@
 #include "bfs_control.h"
 #include "bfs_disk_system.h"
 
+#include <file_systems/fs_ops_support.h>
+
 // TODO: temporary solution as long as there is no public I/O requests API
 #ifndef FS_SHELL
 #	include <io_requests.h>
@@ -1755,14 +1757,10 @@ bfs_read_dir(fs_volume* _volume, fs_vnode* _node, void* _cookie,
 		if (status != B_OK)
 			RETURN_ERROR(status);
 
-		ASSERT(length < nameBufferSize);
-
 		dirent->d_dev = volume->ID();
 		dirent->d_ino = id;
-		dirent->d_reclen = offsetof(struct dirent, d_name) + length + 1;
 
-		bufferSize -= dirent->d_reclen;
-		dirent = (struct dirent*)((uint8*)dirent + dirent->d_reclen);
+		dirent = next_dirent(dirent, length, bufferSize);
 		count++;
 	}