linux-kernel - [PATCH 2/3] tools/nolibc: let FILE streams contain an fd

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Message-Id: <20230328-nolibc-printf-test-v1-2-d7290ec893dd@weissschuh.net>
Date:   Tue, 28 Mar 2023 21:01:30 +0000
From:   Thomas Weißschuh <linux@...ssschuh.net>
To:     Willy Tarreau <w@....eu>, Shuah Khan <shuah@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        Thomas Weißschuh <linux@...ssschuh.net>
Subject: [PATCH 2/3] tools/nolibc: let FILE streams contain an fd

This enables the usage of the stream APIs with arbitrary filedescriptors.

It will be used by a future testcase.
Users can also use nolibc-specific code to do the same.

Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
---
 tools/include/nolibc/stdio.h | 36 +++++++-----------------------------
 1 file changed, 7 insertions(+), 29 deletions(-)

diff --git a/tools/include/nolibc/stdio.h b/tools/include/nolibc/stdio.h
index 96ac8afc5aee..cb58912b98e5 100644
--- a/tools/include/nolibc/stdio.h
+++ b/tools/include/nolibc/stdio.h
@@ -21,17 +21,13 @@
 #define EOF (-1)
 #endif
 
-/* just define FILE as a non-empty type */
 typedef struct FILE {
-	char dummy[1];
+	int fd;
 } FILE;
 
-/* We define the 3 common stdio files as constant invalid pointers that
- * are easily recognized.
- */
-static __attribute__((unused)) FILE* const stdin  = (FILE*)-3;
-static __attribute__((unused)) FILE* const stdout = (FILE*)-2;
-static __attribute__((unused)) FILE* const stderr = (FILE*)-1;
+static __attribute__((unused)) FILE* const stdin  = &(FILE){ STDIN_FILENO  };
+static __attribute__((unused)) FILE* const stdout = &(FILE){ STDOUT_FILENO };
+static __attribute__((unused)) FILE* const stderr = &(FILE){ STDERR_FILENO };
 
 /* getc(), fgetc(), getchar() */
 
@@ -41,14 +37,8 @@ static __attribute__((unused))
 int fgetc(FILE* stream)
 {
 	unsigned char ch;
-	int fd;
 
-	if (stream < stdin || stream > stderr)
-		return EOF;
-
-	fd = 3 + (long)stream;
-
-	if (read(fd, &ch, 1) <= 0)
+	if (read(stream->fd, &ch, 1) <= 0)
 		return EOF;
 	return ch;
 }
@@ -68,14 +58,8 @@ static __attribute__((unused))
 int fputc(int c, FILE* stream)
 {
 	unsigned char ch = c;
-	int fd;
 
-	if (stream < stdin || stream > stderr)
-		return EOF;
-
-	fd = 3 + (long)stream;
-
-	if (write(fd, &ch, 1) <= 0)
+	if (write(stream->fd, &ch, 1) <= 0)
 		return EOF;
 	return ch;
 }
@@ -96,15 +80,9 @@ static __attribute__((unused))
 int _fwrite(const void *buf, size_t size, FILE *stream)
 {
 	ssize_t ret;
-	int fd;
-
-	if (stream < stdin || stream > stderr)
-		return EOF;
-
-	fd = 3 + (long)stream;
 
 	while (size) {
-		ret = write(fd, buf, size);
+		ret = write(stream->fd, buf, size);
 		if (ret <= 0)
 			return EOF;
 		size -= ret;

-- 
2.40.0