[libc] Remove the requirement of a platform-flush operation in File a…

…bstraction.

The libc flush operation is not supposed to trigger a platform level
flush operation. See "Notes" on this Linux man page:
    https://man7.org/linux/man-pages/man3/fflush.3.html

Reviewed By: michaelrj

Differential Revision: https://reviews.llvm.org/D153182

libc/src/__support/File/file.cpp

@@ -335,7 +335,6 @@ int File::flush_unlocked() {
       return buf_result.error;
     }
     pos = 0;
-    return platform_flush(this);
   }
   // TODO: Add POSIX behavior for input streams.
   return 0;

libc/src/__support/File/file.h

@@ -56,7 +56,6 @@ class File {
   // file position indicator.
   using SeekFunc = ErrorOr<long>(File *, long, int);
   using CloseFunc = int(File *);
-  using FlushFunc = int(File *);
   // CleanupFunc is a function which does the equivalent of this:
   //
   // void my_file_cleanup(File *f) {
@@ -103,7 +102,6 @@ class File {
   ReadFunc *platform_read;
   SeekFunc *platform_seek;
   CloseFunc *platform_close;
-  FlushFunc *platform_flush;
   CleanupFunc *platform_cleanup;
 
   Mutex mutex;
@@ -202,15 +200,13 @@ class File {
   // is zero. This way, we will not have to employ the semantics of
   // the set_buffer method and allocate a buffer.
   constexpr File(WriteFunc *wf, ReadFunc *rf, SeekFunc *sf, CloseFunc *cf,
-                 FlushFunc *ff, CleanupFunc *clf, uint8_t *buffer,
-                 size_t buffer_size, int buffer_mode, bool owned,
-                 ModeFlags modeflags)
+                 CleanupFunc *clf, uint8_t *buffer, size_t buffer_size,
+                 int buffer_mode, bool owned, ModeFlags modeflags)
       : platform_write(wf), platform_read(rf), platform_seek(sf),
-        platform_close(cf), platform_flush(ff), platform_cleanup(clf),
-        mutex(false, false, false), ungetc_buf(0), buf(buffer),
-        bufsize(buffer_size), bufmode(buffer_mode), own_buf(owned),
-        mode(modeflags), pos(0), prev_op(FileOp::NONE), read_limit(0),
-        eof(false), err(false) {
+        platform_close(cf), platform_cleanup(clf), mutex(false, false, false),
+        ungetc_buf(0), buf(buffer), bufsize(buffer_size), bufmode(buffer_mode),
+        own_buf(owned), mode(modeflags), pos(0), prev_op(FileOp::NONE),
+        read_limit(0), eof(false), err(false) {
     if constexpr (ENABLE_BUFFER)
       adjust_buf();
   }

libc/src/__support/File/gpu/file.cpp

@@ -26,8 +26,8 @@ class GPUFile : public File {
 
 public:
   constexpr GPUFile(uintptr_t file, File::ModeFlags modeflags)
-      : File(&write_func, nullptr, nullptr, nullptr, nullptr, nullptr, nullptr,
-             0, _IONBF, false, modeflags),
+      : File(&write_func, nullptr, nullptr, nullptr, nullptr, nullptr, 0,
+             _IONBF, false, modeflags),
         file(file) {}
 
   uintptr_t get_file() const { return file; }

libc/src/__support/File/linux/file.cpp

@@ -24,7 +24,6 @@ FileIOResult write_func(File *, const void *, size_t);
 FileIOResult read_func(File *, void *, size_t);
 ErrorOr<long> seek_func(File *, long, int);
 int close_func(File *);
-int flush_func(File *);
 
 } // anonymous namespace
 
@@ -34,7 +33,7 @@ class LinuxFile : public File {
 public:
   constexpr LinuxFile(int file_descriptor, uint8_t *buffer, size_t buffer_size,
                       int buffer_mode, bool owned, File::ModeFlags modeflags)
-      : File(&write_func, &read_func, &seek_func, &close_func, flush_func,
+      : File(&write_func, &read_func, &seek_func, &close_func,
              &cleanup_file<LinuxFile>, buffer, buffer_size, buffer_mode, owned,
              modeflags),
         fd(file_descriptor) {}
@@ -91,15 +90,6 @@ int close_func(File *f) {
   return 0;
 }
 
-int flush_func(File *f) {
-  auto *lf = reinterpret_cast<LinuxFile *>(f);
-  int ret = __llvm_libc::syscall_impl(SYS_fsync, lf->get_fd());
-  if (ret < 0) {
-    return -ret;
-  }
-  return 0;
-}
-
 } // anonymous namespace
 
 ErrorOr<File *> openfile(const char *path, const char *mode) {

libc/src/stdio/fopencookie.cpp

@@ -26,15 +26,13 @@ class CookieFile : public __llvm_libc::File {
   static FileIOResult cookie_read(File *f, void *data, size_t size);
   static ErrorOr<long> cookie_seek(File *f, long offset, int whence);
   static int cookie_close(File *f);
-  static int cookie_flush(File *);
 
 public:
   CookieFile(void *c, cookie_io_functions_t cops, uint8_t *buffer,
              size_t bufsize, File::ModeFlags mode)
       : File(&cookie_write, &cookie_read, &CookieFile::cookie_seek,
-             &cookie_close, &cookie_flush, &cleanup_file<CookieFile>, buffer,
-             bufsize, 0 /* default buffering mode */,
-             true /* File owns buffer */, mode),
+             &cookie_close, &cleanup_file<CookieFile>, buffer, bufsize,
+             0 /* default buffering mode */, true /* File owns buffer */, mode),
         cookie(c), ops(cops) {}
 };
 
@@ -74,8 +72,6 @@ int CookieFile::cookie_close(File *f) {
   return cookie_file->ops.close(cookie_file->cookie);
 }
 
-int CookieFile::cookie_flush(File *) { return 0; }
-
 } // anonymous namespace
 
 LLVM_LIBC_FUNCTION(::FILE *, fopencookie,

libc/test/src/__support/File/file_test.cpp

@@ -33,13 +33,12 @@ class StringFile : public File {
                                 size_t len);
   static ErrorOr<long> str_seek(__llvm_libc::File *f, long offset, int whence);
   static int str_close(__llvm_libc::File *f) { return 0; }
-  static int str_flush(__llvm_libc::File *f) { return 0; }
 
 public:
   explicit StringFile(char *buffer, size_t buflen, int bufmode, bool owned,
                       ModeFlags modeflags)
       : __llvm_libc::File(&str_write, &str_read, &str_seek, &str_close,
-                          &str_flush, &__llvm_libc::cleanup_file<StringFile>,
+                          &__llvm_libc::cleanup_file<StringFile>,
                           reinterpret_cast<uint8_t *>(buffer), buflen, bufmode,
                           owned, modeflags),
         pos(0), eof_marker(0), write_append(false) {

libc/test/src/stdio/ftell_test.cpp

@@ -7,7 +7,6 @@
 //===----------------------------------------------------------------------===//
 
 #include "src/stdio/fclose.h"
-#include "src/stdio/fflush.h"
 #include "src/stdio/fopen.h"
 #include "src/stdio/fread.h"
 #include "src/stdio/fseek.h"