kern: os: Add I/O tap framework

The I/O tap framework provides a way to bypass the typical device
filesystem interface for applications where more direct access would be
beneficial.

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

1 files changed, 82 insertions, 0 deletions

diff --git a/src/sys/include/os/iotap.h b/src/sys/include/os/iotap.h
new file mode 100644
index 0000000..7421bf1
--- /dev/null
+++ b/src/sys/include/os/iotap.h
@@ -0,0 +1,82 @@
+/*
+ * 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 _OS_IOTAP_H_
+#define _OS_IOTAP_H_ 1
+
+#include <sys/types.h>
+#include <sys/queue.h>
+
+struct iotap_desc;
+typedef int16_t iotap_t;
+
+struct iotap_ops {
+    ssize_t(*read)(struct iotap_desc *desc, void *p, size_t len);
+};
+
+/*
+ * Represents an I/O tap descriptor used to interface
+ * with a device
+ *
+ * @name: I/O tap name
+ * @id: ID of I/O tap
+ * @ops: I/O tap operations
+ *
+ * XXX: When registering an I/O tap, leave `id' unset as it will
+ *      be filled by the registration logic.
+ */
+struct iotap_desc {
+    char *name;
+    iotap_t id;
+    struct iotap_ops *ops;
+};
+
+/*
+ * Register an I/O tap interface
+ *
+ * @iotap: I/O tap interface descriptor to register
+ *
+ * Returns an I/O table ID as a handle on success,
+ * otherwise a less than zero value on failure.
+ */
+iotap_t iotap_register(const struct iotap_desc *iotap);
+
+/*
+ * Look up an I/O tap by name
+ *
+ * @name: Name of I/O tap to look up
+ * @dp_res: I/O tap descriptor result
+ *
+ * Returns zero on success with a result
+ * assigned to `dp`, otherwise a less than
+ * zero value on failure.
+ */
+int iotap_lookup(const char *name, struct iotap_desc *dp_res);
+
+#endif  /* !_OS_IOTAP_H_ */