LibC: Implement basic dirent functionality

We don't currently support seeking

libc/CMakeLists.txt

@@ -5,6 +5,7 @@ project(libc CXX ASM)
 set(LIBC_SOURCES
 	assert.cpp
 	ctype.cpp
+	dirent.cpp
 	fcntl.cpp
 	printf_impl.cpp
 	stdio.cpp

libc/dirent.cpp

@@ -0,0 +1,92 @@
+#include <dirent.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+#include <kernel/API/DirectoryEntry.h>
+
+struct __DIR
+{
+	int fd { -1 };
+	size_t entry_index { 0 };
+	Kernel::API::DirectoryEntry* current { nullptr };
+
+	size_t buffer_size { 0 };
+	Kernel::API::DirectoryEntryList buffer[];
+};
+
+int closedir(DIR* dirp)
+{
+	if (dirp == nullptr || dirp->fd == -1)
+	{
+		errno = EBADF;
+		return -1;
+	}
+	
+	close(dirp->fd);
+	dirp->fd = -1;
+	free(dirp);
+
+	return 0;
+}
+
+int dirfd(DIR* dirp)
+{
+	if (dirp == nullptr || dirp->fd == -1)
+	{
+		errno = EINVAL;
+		return -1;
+	}
+
+	return dirp->fd;
+}
+
+DIR* fdopendir(int fd)
+{
+	DIR* dirp = (DIR*)malloc(sizeof(DIR) + 4096);
+	if (dirp == nullptr)
+		return nullptr;
+
+	dirp->fd = fd;
+	dirp->current = nullptr;
+	dirp->buffer_size = 4096;
+
+	return dirp;
+}
+
+DIR* opendir(const char* dirname)
+{
+	int fd = open(dirname, O_SEARCH);
+	if (fd == -1)
+		return nullptr;
+	return fdopendir(fd);
+}
+
+struct dirent* readdir(DIR* dirp)
+{
+	if (dirp == nullptr || dirp->fd == -1)
+	{
+		errno = EBADF;
+		return nullptr;
+	}
+
+	dirp->entry_index++;
+	if (dirp->current && dirp->entry_index < dirp->buffer->entry_count)
+	{
+		dirp->current = dirp->current->next();
+		return &dirp->current->dirent;
+	}
+
+	if (syscall(SYS_READ_DIR_ENTRIES, dirp->fd, dirp->buffer, dirp->buffer_size) == -1)
+		return nullptr;
+
+	if (dirp->buffer->entry_count == 0)
+		return nullptr;
+
+	dirp->entry_index = 0;
+	dirp->current = dirp->buffer->array;
+
+	return &dirp->current->dirent;
+}

libc/include/dirent.h

@@ -10,8 +10,8 @@ __BEGIN_DECLS
 #define __need_ino_t
 #include <sys/types.h>
 
-struct DIR;
+struct __DIR;
-typedef struct DIR DIR;
+typedef struct __DIR DIR;
 
 struct dirent
 {