kern: iotap: Expose I/O taps to userland

Expose I/O taps to userland using a tap message interface. An
application may construct a tap message to send to the kernel requesting
data from a specific tap, if there is data, the buffers will be safely
populated, otherwise some error returned.

An example is accessing the PS/2 keyboard tap:

--

char name[] = "i8042.port.0";
char buf[2] = {0, 0};
struct iotap_msg msg = {
    .opcode = IOTAP_OPC_READ,
    .buf = buf,
    .len = len
};

...

/* muxtap() may be used */

...
--

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

1 files changed, 58 insertions, 0 deletions

diff --git a/src/sys/include/sys/iotap.h b/src/sys/include/sys/iotap.h
new file mode 100644
index 0000000..10e4f82
--- /dev/null
+++ b/src/sys/include/sys/iotap.h
@@ -0,0 +1,58 @@
+/*
+ * Copyright (c) 2025 Ian Marco Moffett and L5 engineers
+ * 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 the project 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.
+ */
+
+#ifndef _SYS_IOTAP_H_
+#define _SYS_IOTAP_H_ 1
+
+#include <sys/types.h>
+#include <sys/cdefs.h>
+#if !defined(_KERNEL)
+#include <stdint.h>
+#include <stddef.h>
+#endif  /* _KERNEL */
+
+/* Valid I/O tap opcodes */
+#define IOTAP_OPC_READ       0x0000
+
+/*
+ * An I/O tap message that can be send to
+ * the kernel to perform an operation on
+ * a tap.
+ *
+ * @opcode: Operation to be performed
+ * @buf: I/O buffer read/write operations
+ * @len: Length of I/O buffer
+ */
+struct __packed iotap_msg {
+    uint8_t opcode;
+    void *buf;
+    size_t len;
+};
+
+#endif  /* _SYS_IOTAP_H_ */