1 files changed, 84 insertions, 0 deletions
diff --git a/lib/libc/stdio/fflush.c b/lib/libc/stdio/fflush.c
new file mode 100644
index 00000000..f9a2004d
--- /dev/null
+++ b/lib/libc/stdio/fflush.c
@@ -0,0 +1,84 @@
+#include <stdio.h>
+#include <unistd.h>
+#include <atomic.h>
+#include <io.h>
+#include <errno.h>
+#include <string.h>
+
+int fflush(FILE *stream)
+{
+	// Handle NULL stream - flush all open streams
+	if (stream == NULL) {
+		// TODO: Implement flushing all open streams
+		// For now, just return success
+		return 0;
+	}
+
+	// Nothing to flush if buffer is empty
+	if (stream->buf_len == 0) {
+		return 0;
+	}
+
+	// Handle special case of invalid file descriptor
+	if (stream->fd == -1) {
+		stream->buf_len = 0;
+		return 0;
+	}
+
+	// Check if stream is in error state
+	if (stream->flags & _IO_ERR) {
+		errno = EIO;
+		return EOF;
+	}
+
+	// Check if stream is writable
+	if ((stream->flags & O_ACCMODE) == O_RDONLY) {
+		errno = EBADF;
+		return EOF;
+	}
+
+	LIBC_LOCK(stream->lock);
+
+	size_t bytes_to_write = stream->buf_len;
+	size_t total_written = 0;
+	char *buf_ptr = stream->buf;
+
+	// Write all buffered data
+	while (total_written < bytes_to_write) {
+		ssize_t result = write(stream->fd, buf_ptr + total_written,
+				       bytes_to_write - total_written);
+
+		if (result < 0) {
+			// Write error occurred
+			stream->flags |= _IO_ERR;
+			LIBC_UNLOCK(stream->lock);
+			return EOF;
+		}
+
+		if (result == 0) {
+			// No progress made (shouldn't happen with regular
+			// files)
+			break;
+		}
+
+		total_written += result;
+	}
+
+	// Update buffer state
+	if (total_written == bytes_to_write) {
+		// All data was written successfully
+		stream->buf_len = 0;
+		stream->buf_pos = 0;
+	} else {
+		// Partial write - move remaining data to beginning of buffer
+		size_t remaining = bytes_to_write - total_written;
+		memmove(stream->buf, stream->buf + total_written, remaining);
+		stream->buf_len = remaining;
+		stream->buf_pos = 0;
+	}
+
+	LIBC_UNLOCK(stream->lock);
+
+	// Return success if all data was written, error otherwise
+	return (total_written == bytes_to_write) ? 0 : EOF;
+}