Add support for reading hypervisor console (#344)

* feature(xencall): add hypervisor SYSCTL_readconsole definitions

* feature(hypervisor-dmesg): xencall: add read_console_ring_raw hypercall wrapper

* feature(hypervisor-dmesg): protobuf: add ReadHypervisorConsoleRing RPC

* feature(hypervisor-dmesg): runtime: add read_hypervisor_console wrapper

* feature(hypervisor-dmesg): daemon: add ReadHypervisorConsoleRing rpc implementation

* feature(hypervisor-dmesg): ctl: add host hypervisor-messages command to get hypervisor messages

* feature(hypervisor-dmesg): cli: rename hypervisor-messages command to hv-console

* feature(hypervisor-dmesg): proto: change ReadHypervisorConsoleRing to ReadHypervisorConsole

* feature(hypervisor-dmesg): fix up kratactl protobuf calls

crates/xen/xencall/examples/console_read.rs

@@ -0,0 +1,18 @@
+use xencall::error::Result;
+use xencall::XenCall;
+
+#[tokio::main]
+async fn main() -> Result<()> {
+    env_logger::init();
+
+    let call = XenCall::open(0)?;
+    let index = 0 as u32;
+    let (buf, newindex) = call.read_console_ring_raw(false, index).await?;
+
+    match std::str::from_utf8(&buf[..newindex as usize]) {
+        Ok(v) => print!("{}", v),
+        _ => panic!("unable to decode Xen console messages"),
+    };
+
+    Ok(())
+}

crates/xen/xencall/src/lib.rs

@@ -26,12 +26,12 @@ use std::sync::Arc;
 use std::time::Duration;
 use sys::{
     CpuId, E820Entry, ForeignMemoryMap, PhysdevMapPirq, Sysctl, SysctlCputopo, SysctlCputopoinfo,
-    SysctlPhysinfo, SysctlPmOp, SysctlPmOpValue, SysctlSetCpuFreqGov, SysctlValue,
+    SysctlPhysinfo, SysctlPmOp, SysctlPmOpValue, SysctlSetCpuFreqGov, SysctlValue, SysctlReadconsole,
     VcpuGuestContextAny, HYPERVISOR_PHYSDEV_OP, HYPERVISOR_SYSCTL, PHYSDEVOP_MAP_PIRQ,
     XEN_DOMCTL_MAX_INTERFACE_VERSION, XEN_DOMCTL_MIN_INTERFACE_VERSION, XEN_MEM_SET_MEMORY_MAP,
     XEN_SYSCTL_CPUTOPOINFO, XEN_SYSCTL_MAX_INTERFACE_VERSION, XEN_SYSCTL_MIN_INTERFACE_VERSION,
     XEN_SYSCTL_PHYSINFO, XEN_SYSCTL_PM_OP, XEN_SYSCTL_PM_OP_DISABLE_TURBO,
-    XEN_SYSCTL_PM_OP_ENABLE_TURBO, XEN_SYSCTL_PM_OP_SET_CPUFREQ_GOV,
+    XEN_SYSCTL_PM_OP_ENABLE_TURBO, XEN_SYSCTL_PM_OP_SET_CPUFREQ_GOV, XEN_SYSCTL_READCONSOLE,
 };
 use tokio::sync::Semaphore;
 use tokio::time::sleep;
@@ -1087,4 +1087,31 @@ impl XenCall {
             .await?;
         Ok(())
     }
+
+    pub async fn read_console_ring_raw(&self, clear: bool, index: u32) -> Result<([u8; 16384], u32)> {
+        let mut u8buf = [0u8; 16384];
+        let mut sysctl = Sysctl {
+            cmd: XEN_SYSCTL_READCONSOLE,
+            interface_version: self.sysctl_interface_version,
+            value: SysctlValue {
+                console: SysctlReadconsole {
+                    clear: clear as u8,
+                    incremental: 1,
+                    pad: 0,
+                    index: index,
+                    buffer: addr_of_mut!(u8buf) as u64,
+                    count: 16384,
+                },
+            },
+        };
+        self.hypercall1(HYPERVISOR_SYSCTL, addr_of_mut!(sysctl) as c_ulong)
+            .await?;
+        // Safety: We are passing a SysctlReadconsole struct as part of the hypercall, and
+        // calling the hypercall is known to not change the underlying value outside changing
+        // the values on some SysctlReadconsole fields.
+        let newindex = unsafe {
+            sysctl.value.console.index
+        };
+        Ok((u8buf, newindex))
+    }
 }

crates/xen/xencall/src/sys.rs

@@ -752,6 +752,7 @@ pub struct SysctlCputopoinfo {
 
 #[repr(C)]
 pub union SysctlValue {
+    pub console: SysctlReadconsole,
     pub cputopoinfo: SysctlCputopoinfo,
     pub pm_op: SysctlPmOp,
     pub phys_info: SysctlPhysinfo,
@@ -765,6 +766,7 @@ pub struct Sysctl {
     pub value: SysctlValue,
 }
 
+pub const XEN_SYSCTL_READCONSOLE: u32 = 1;
 pub const XEN_SYSCTL_PHYSINFO: u32 = 3;
 pub const XEN_SYSCTL_PM_OP: u32 = 12;
 pub const XEN_SYSCTL_CPUTOPOINFO: u32 = 16;
@@ -802,3 +804,14 @@ pub struct SysctlPhysinfo {
     pub max_mfn: u64,
     pub hw_cap: [u32; 8],
 }
+
+#[repr(C)]
+#[derive(Clone, Copy, Debug, Default)]
+pub struct SysctlReadconsole {
+    pub clear: u8,
+    pub incremental: u8,
+    pub pad: u16,
+    pub index: u32,
+    pub buffer: u64,
+    pub count: u32,
+}