tools/nolibc: Add fread() to stdio.h

Add a very basic version of fread() like we already have for fwrite().

Signed-off-by: Daniel Palmer <daniel@thingy.jp>
Link: https://patch.msgid.link/20260105023629.1502801-2-daniel@thingy.jp
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>

tools/include/nolibc/stdio.h

@@ -170,7 +170,7 @@ int putchar(int c)
 }
 
 
-/* fwrite(), puts(), fputs(). Note that puts() emits '\n' but not fputs(). */
+/* fwrite(), fread(), puts(), fputs(). Note that puts() emits '\n' but not fputs(). */
 
 /* internal fwrite()-like function which only takes a size and returns 0 on
  * success or EOF on error. It automatically retries on short writes.
@@ -204,6 +204,38 @@ size_t fwrite(const void *s, size_t size, size_t nmemb, FILE *stream)
 	return written;
 }
 
+/* internal fread()-like function which only takes a size and returns 0 on
+ * success or EOF on error. It automatically retries on short reads.
+ */
+static __attribute__((unused))
+int _fread(void *buf, size_t size, FILE *stream)
+{
+	int fd = fileno(stream);
+	ssize_t ret;
+
+	while (size) {
+		ret = read(fd, buf, size);
+		if (ret <= 0)
+			return EOF;
+		size -= ret;
+		buf += ret;
+	}
+	return 0;
+}
+
+static __attribute__((unused))
+size_t fread(void *s, size_t size, size_t nmemb, FILE *stream)
+{
+	size_t nread;
+
+	for (nread = 0; nread < nmemb; nread++) {
+		if (_fread(s, size, stream) != 0)
+			break;
+		s += size;
+	}
+	return nread;
+}
+
 static __attribute__((unused))
 int fputs(const char *s, FILE *stream)
 {