[libc] add fileno function for Linux

[michaelrj]

libc/src/stdio/fileno.cpp

3

nit: line formatting

[alfredfo]

fix format

[sivachandra]

libc/config/linux/x86_64/entrypoints.txt

430

Can we add this to the other configs also?

libc/src/stdio/fileno.cpp

19

This is not a fully evolved API yet. For example, the Linux implementation does not try to check if stream is actually a file stream. But, we have not yet decided if the get_fileno should be responsible to perform that check, or if it is the job of this function to perform that check. It feels like we should have some kind of flag maintained in the File data structure to indicate whether stream has a number or not. Let me think about this and get back. If you have any better suggestions to make, feel free to share.

[alfredfo]

add tests

[alfredfo]

@sivachandra: Yes, I also wondered about that (re: "Linux implementation does not try to check if stream is actually a file stream"). I don't know what the best solution is. I tried both glibc and llvm-libc with invalid stream as argument and both crashed. Seems like musl libc also just assumes that the file ptr is valid https://elixir.bootlin.com/musl/latest/source/src/stdio/fileno.c#L7

[alfredfo]

libc/config/linux/x86_64/entrypoints.txt

430

do you mean in config/linux/*every arch that works*/entrypoints.txt ? The get_fileno function is currently only implemented for Linux.

libc/config/linux/x86_64/entrypoints.txt

list(APPEND TARGET_LIBC_ENTRYPOINTS
     libc.src.stdio.feof
     libc.src.stdio.feof_unlocked
     libc.src.stdio.ferror
     libc.src.stdio.ferror_unlocked
     libc.src.stdio.fgetc
     libc.src.stdio.fgetc_unlocked
     libc.src.stdio.fgets
     libc.src.stdio.fflush
+    libc.src.stdio.fileno
     libc.src.stdio.fopen
     libc.src.stdio.fputc
     libc.src.stdio.fputs
     libc.src.stdio.fopencookie
     libc.src.stdio.fread
     libc.src.stdio.fread_unlocked
     libc.src.stdio.fseek
     libc.src.stdio.ftell

libc/spec/posix.td

 
   HeaderSpec StdIO = HeaderSpec<
       "stdio.h",
       [], // Macros
       [], // Types
       [], // Enumerations
       [
           FunctionSpec<
+              "fileno",
+              RetValSpec<IntType>,
+              [ArgSpec<FILEPtr>]
+          >,
+          FunctionSpec<
               "flockfile",
               RetValSpec<VoidType>,
               [ArgSpec<FILEPtr>]
           >,
           FunctionSpec<
               "funlockfile",
               RetValSpec<VoidType>,
               [ArgSpec<FILEPtr>]

libc/src/stdio/CMakeLists.txt

add_entrypoint_object(
   DEPENDS
     libc.src.errno.errno
     libc.include.stdio
     libc.src.__support.File.file
     libc.src.__support.File.platform_file
 )
 
 add_entrypoint_object(
+  fileno
+  SRCS
+    fileno.cpp
+  HDRS
+    fileno.h
+  DEPENDS
+    libc.src.errno.errno
+    libc.include.stdio
+    libc.src.__support.File.file
+    libc.src.__support.File.platform_file
+)
+
+add_entrypoint_object(
   getc
   SRCS
     getc.cpp
   HDRS
     getc.h
   DEPENDS
     libc.src.errno.errno
     libc.include.stdio

libc/src/stdio/fileno.h

+//===-- Implementation header of fileno -------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STDIO_FILENO_H
+#define LLVM_LIBC_SRC_STDIO_FILENO_H
+
+#include <stdio.h>
+
+namespace __llvm_libc {
+
+int fileno(::FILE *stream);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_STDIO_FILENO_H

libc/src/stdio/fileno.cpp

+//===-- Implementation of fileno ------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/stdio/fileno.h"
+#include "src/__support/File/file.h"
+
+#include "src/errno/libc_errno.h"
+#include <stdio.h>
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(int, fileno, (::FILE *__restrict stream)) {
+  auto fd = get_fileno(reinterpret_cast<__llvm_libc::File *>(stream));
+
+  if (fd >= 0) {
+    return fd;
+  } else {
+    libc_errno = EBADF;
+    return -1;
+  }
+}
+
+} // namespace __llvm_libc

libc/test/src/stdio/CMakeLists.txt

DEPENDS
     libc.src.stdio.feof
     libc.src.stdio.ferror
     libc.src.stdio.fgets
     libc.src.stdio.fopen
     libc.src.stdio.fwrite
 )
 
 add_libc_unittest(
+  fileno_test
+  SUITE
+    libc_stdio_unittests
+  SRCS
+    fileno_test.cpp
+  DEPENDS
+    libc.include.stdio
+    libc.src.stdio.fopen
+    libc.src.stdio.fileno
+)
+
+add_libc_unittest(
   ftell_test
   SUITE
     libc_stdio_unittests
   SRCS
     ftell_test.cpp
   DEPENDS
     libc.include.stdio
     libc.src.stdio.fclose

libc/test/src/stdio/fileno_test.cpp

+//===-- Unittests for fileno ----------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/__support/File/file.h"
+#include "src/stdio/fileno.h"
+#include "src/stdio/fopen.h"
+#include "test/UnitTest/Test.h"
+#include <stdio.h>
+
+TEST(LlvmLibcFilenoTest, ValidFilenoTest) {
+  ::FILE *file = __llvm_libc::fopen("testdata/test_data.txt", "w");
+  ASSERT_FALSE(file == nullptr);
+
+  // file descriptors associated with the streams stdin, stdout, and stderr are
+  // 0, 1, and 2, respectively. Therefore any newly opened file should have an
+  // integer file descriptor >= 3
+
+  ASSERT_FALSE(__llvm_libc::fileno(file) < 3);
+}
+
+TEST(LlvmLibcFilenoTest, StandardStreamTest) {
+  ASSERT_EQ(__llvm_libc::fileno(reinterpret_cast<FILE *>(__llvm_libc::stdin)),
+            0);
+  ASSERT_EQ(__llvm_libc::fileno(reinterpret_cast<FILE *>(__llvm_libc::stdout)),
+            1);
+  ASSERT_EQ(__llvm_libc::fileno(reinterpret_cast<FILE *>(__llvm_libc::stderr)),
+            2);
+}