[libc] Enable linux directory entries syscalls in riscv64

This patch updates the struct dirent to be on par with glibc (by adding
a missing d_type member) and update the readdir call to use SYS_getdents64
instead of SYS_getdents.

Reviewed By: sivachandra

Differential Revision: https://reviews.llvm.org/D147738

libc/config/linux/riscv64/entrypoints.txt

@@ -341,6 +341,12 @@ if(LLVM_LIBC_FULL_BUILD)
     # assert.h entrypoints
     libc.src.assert.__assert_fail
 
+    # dirent.h entrypoints
+    libc.src.dirent.closedir
+    libc.src.dirent.dirfd
+    libc.src.dirent.opendir
+    libc.src.dirent.readdir
+
     # network.h entrypoints
     libc.src.network.htonl
     libc.src.network.htons

libc/config/linux/riscv64/headers.txt

@@ -1,6 +1,7 @@
 set(TARGET_PUBLIC_HEADERS
     libc.include.assert
     libc.include.ctype
+    libc.include.dirent
     libc.include.errno
     libc.include.fcntl
     libc.include.fenv

libc/include/llvm-libc-types/struct_dirent.h

@@ -18,6 +18,7 @@ struct dirent {
   off_t d_off;
   unsigned short d_reclen;
 #endif
+  unsigned char d_type;
   // The user code should use strlen to determine actual the size of d_name.
   // Likewise, it is incorrect and prohibited by the POSIX standard to detemine
   // the size of struct dirent type using sizeof. The size should be got using

libc/src/__support/File/CMakeLists.txt

@@ -11,7 +11,6 @@ add_object_library(
   HDRS
     file.h
   DEPENDS
-
     libc.src.__support.CPP.new
     libc.src.__support.CPP.span
     libc.src.__support.threads.mutex
@@ -37,7 +36,6 @@ if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS}_file.cpp)
       ${LIBC_TARGET_OS}_file.cpp
     DEPENDS
       .file
-
       libc.include.fcntl
       libc.include.stdio
       libc.include.sys_syscall

libc/src/__support/File/dir.cpp

@@ -12,8 +12,6 @@
 #include "src/__support/error_or.h"
 #include "src/errno/libc_errno.h" // For error macros
 
-#include <stdlib.h>
-
 namespace __llvm_libc {
 
 ErrorOr<Dir *> Dir::open(const char *path) {

libc/src/__support/File/linux_dir.cpp

@@ -34,8 +34,13 @@ ErrorOr<int> platform_opendir(const char *name) {
 }
 
 ErrorOr<size_t> platform_fetch_dirents(int fd, cpp::span<uint8_t> buffer) {
-  long size =
-      __llvm_libc::syscall_impl(SYS_getdents, fd, buffer.data(), buffer.size());
+#ifdef SYS_getdents64
+  long size = __llvm_libc::syscall_impl(SYS_getdents64, fd, buffer.data(),
+                                        buffer.size());
+#else
+#error "getdents64 syscalls not available to perform a fetch dirents operation."
+#endif
+
   if (size < 0) {
     return __llvm_libc::Error(static_cast<int>(-size));
   }