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>

4 files changed, 84 insertions, 1 deletions

diff --git a/src/sys/include/compat/unix/syscall.h b/src/sys/include/compat/unix/syscall.h
index 5945f75..743e50c 100644
--- a/src/sys/include/compat/unix/syscall.h
+++ b/src/sys/include/compat/unix/syscall.h
@@ -34,6 +34,7 @@
 #include <sys/param.h>
 #include <sys/mount.h>
 #include <sys/syscall.h>
+#include <os/iotap.h>
 
 /*
  * Exit the current process - exit(2) syscall
@@ -69,7 +70,8 @@ scret_t(*g_unix_sctab[])(struct syscall_args *) = {
     [SYS_query]  = sys_query,
     [SYS_spawn]  = sys_spawn,
     [SYS_mount]  = sys_mount,
-    [SYS_open]   = sys_open
+    [SYS_open]   = sys_open,
+    [SYS_muxtap] = sys_muxtap
 };
 
 #endif  /* !_NEED_UNIX_SCTAB */
diff --git a/src/sys/include/os/iotap.h b/src/sys/include/os/iotap.h
index 7421bf1..baef59c 100644
--- a/src/sys/include/os/iotap.h
+++ b/src/sys/include/os/iotap.h
@@ -32,6 +32,11 @@
 
 #include <sys/types.h>
 #include <sys/queue.h>
+#include <sys/iotap.h>
+#include <sys/syscall.h>
+#include <os/mac.h>
+
+#define IOTAP_MSG_MAX 1024
 
 struct iotap_desc;
 typedef int16_t iotap_t;
@@ -79,4 +84,21 @@ iotap_t iotap_register(const struct iotap_desc *iotap);
  */
 int iotap_lookup(const char *name, struct iotap_desc *dp_res);
 
+/*
+ * Handle an I/O tap message and perform operations
+ * using specific commands.
+ *
+ * @name: Name of tap to operate on
+ * @msg: Message to send
+ *
+ * Returns less than zero values on failure, other
+ * values depend on the input command.
+ */
+ssize_t iotap_mux(const char *name, struct iotap_msg *msg);
+
+/*
+ * Perform an operation on an I/O tap
+ */
+scret_t sys_muxtap(struct syscall_args *scargs);
+
 #endif  /* !_OS_IOTAP_H_ */
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_ */
diff --git a/src/sys/include/sys/syscall.h b/src/sys/include/sys/syscall.h
index 181f734..09996ae 100644
--- a/src/sys/include/sys/syscall.h
+++ b/src/sys/include/sys/syscall.h
@@ -51,6 +51,7 @@
 #define SYS_spawn       0x06    /* spawn a process */
 #define SYS_mount       0x07    /* mount a filesystem */
 #define SYS_open        0x08    /* open a file */
+#define SYS_muxtap      0x09 /* mux an I/O tap */
 
 typedef __ssize_t scret_t;
 typedef __ssize_t scarg_t;