Add probe_ops function for discovering available io_uring features

src/io_uring/constants.rs

@@ -60,3 +60,9 @@ pub const IORING_REGISTER_EVENTFD: u32 = 4;
 pub const IORING_UNREGISTER_EVENTFD: u32 = 5;
 pub const IORING_REGISTER_FILES_UPDATE: u32 = 6;
 pub const IORING_REGISTER_EVENTFD_ASYNC: u32 = 7;
+pub const IORING_REGISTER_PROBE: u32 = 8;
+pub const IORING_REGISTER_PERSONALITY: u32 = 9;
+pub const IORING_UNREGISTER_PERSONALITY: u32 = 10;
+pub const IORING_REGISTER_RESTRICTIONS: u32 = 11;
+pub const IORING_REGISTER_ENABLE_RINGS: u32 = 12;
+

src/io_uring/kernel_types.rs

@@ -163,3 +163,38 @@ pub struct io_cqring_offsets {
     pub cqes: u32,
     pub resv: [u64; 2_usize],
 }
+
+#[repr(C)]
+#[derive(Default, Debug, Copy, Clone)]
+pub struct io_uring_probe_op {
+	pub op: u8,
+	pub resv: u8,
+    pub flags: u16,/* IO_URING_OP_* flags */
+    pub resv2: u32,
+}
+
+#[repr(C)]
+#[derive(Debug, Copy, Clone)]
+pub struct io_uring_probe {
+    pub last_op: u8, /* last opcode supported */
+	pub ops_len: u8, /* length of ops[] array below */
+	pub resv: u16,
+    pub resv2: [u32; 3_usize],
+
+    // This is a variable length field in C, but the usual call
+    // to get all available ops would always use 256
+    pub ops: [io_uring_probe_op; 256]
+}
+
+impl Default for io_uring_probe {
+    fn default() -> Self {
+        Self {
+            last_op: 0,
+            ops_len: 0,
+            resv: 0,
+            resv2: [0; 3],
+            ops: [io_uring_probe_op::default(); 256]
+        }
+    }
+
+}

src/io_uring/uring.rs

@@ -1,4 +1,6 @@
 use super::*;
+use crate::io_uring::syscall::register;
+use crate::io_uring::kernel_types::{io_uring_probe, io_uring_probe_op};
 
 /// Nice bindings for the shiny new linux IO system
 #[derive(Debug, Clone)]
@@ -77,6 +79,30 @@ impl Uring {
         }
     }
 
+    /// Gets a list of io_uring opcodes supported by the
+    /// running kernel.
+    ///
+    /// # Warning
+    ///
+    /// This only becomes usable on linux kernels
+    /// 5.6 and up.
+    pub fn probe_ops(
+        &self
+    ) -> io::Result<Vec<io_uring_probe_op>>
+    {
+        let probe = io_uring_probe::default();
+        let probe_ptr: *const io_uring_probe = &probe;
+
+        register(
+            self.ring_fd.as_raw_fd(),
+            IORING_REGISTER_PROBE,
+            probe_ptr as *const libc::c_void,
+            256
+        )?;
+
+        Ok(probe.ops[0..probe.last_op as usize + 1].into())
+    }
+
     pub(crate) fn ensure_submitted(
         &self,
         sqe_id: u64,