usr: libc: Add fileno()

Add POSIX fileno() to grab a file descriptor number from a stream
pointer.

Signed-off-by: Ian Moffett <ian@osmora.org>

2 files changed, 37 insertions, 0 deletions

diff --git a/lib/libc/include/stdio.h b/lib/libc/include/stdio.h
index 88e66f6..4bbe81a 100644
--- a/lib/libc/include/stdio.h
+++ b/lib/libc/include/stdio.h
@@ -79,6 +79,7 @@ int vsnprintf(char *s, size_t size, const char *fmt, va_list ap);
 int snprintf(char *s, size_t size, const char *fmt, ...);
 
 int printf(const char *__restrict fmt, ...);
+int fileno(FILE *stream);
 int fputc(int c, FILE *stream);
 
 int putchar(int c);
diff --git a/lib/libc/src/stdio/file.c b/lib/libc/src/stdio/file.c
new file mode 100644
index 0000000..5c84c35
--- /dev/null
+++ b/lib/libc/src/stdio/file.c
@@ -0,0 +1,36 @@
+/*
+ * Copyright (c) 2023-2025 Ian Marco Moffett and the Osmora Team.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of Hyra nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <stdio.h>
+
+int
+fileno(FILE *stream)
+{
+    return stream->fd;
+}