Fix crashdump creation message print when the option is disabled for a sandbox

- Update docs to add a note about how to disable crashdumps for specific
  sandboxes
- Commit automatically update `Cargo.lock` for rust_guests

Signed-off-by: Doru Blânzeanu <dblnz@pm.me>

Author: dblnz

docs/how-to-debug-a-hyperlight-guest.md

@@ -211,6 +211,13 @@ To make Hyperlight dump the state of the vCPU (general purpose registers, regist
 This will result in a dump file being created in the temporary directory.
 The name and location of the dump file will be printed to the console and logged as an error message.
 
+**NOTE**: By enabling the `crashdump` feature, you instruct Hyperlight to create core dump files for all sandboxes when an unhandled crash occurs.
+To selectively disable this feature for a specific sandbox, you can set the `guest_core_dump` field to `false` in the `SandboxConfiguration`.
+```rust
+    let mut cfg = SandboxConfiguration::default();
+    cfg.set_guest_core_dump(false); // Disable core dump for this sandbox
+```
+
 ### Inspecting the core dump
 
 After the core dump has been created, to inspect the state of the guest, load the core dump file using `gdb` or `lldb`.

src/hyperlight_host/src/hypervisor/crashdump.rs

@@ -263,8 +263,6 @@ impl ReadProcessMemory for GuestMemReader {
 /// # Returns
 /// * `Result<()>`: Success or error
 pub(crate) fn generate_crashdump(hv: &dyn Hypervisor) -> Result<()> {
-    log::info!("Creating core dump file...");
-
     // Get crash context from hypervisor
     let ctx = hv
         .crashdump_context()
@@ -284,10 +282,16 @@ pub(crate) fn generate_crashdump(hv: &dyn Hypervisor) -> Result<()> {
         ) as Box<dyn Write>)
     };
 
-    checked_core_dump(ctx, create_dump_file).map(|_| {
-        println!("Core dump created successfully: {}", file_path);
-        log::error!("Core dump file: {}", file_path);
-    })
+    if let Ok(nbytes) = checked_core_dump(ctx, create_dump_file) {
+        if nbytes > 0 {
+            println!("Core dump created successfully: {}", file_path);
+            log::error!("Core dump file: {}", file_path);
+        }
+    } else {
+        log::error!("Failed to create core dump file");
+    }
+
+    Ok(())
 }
 
 /// Computes the file path for the core dump file.
@@ -352,6 +356,8 @@ fn checked_core_dump(
     // If the HV returned a context it means we can create a core dump
     // This is the case when the sandbox has been configured at runtime to allow core dumps
     if let Some(ctx) = ctx {
+        log::info!("Creating core dump file...");
+
         // Set up data sources for the core dump
         let guest_view = GuestView::new(&ctx);
         let memory_reader = GuestMemReader::new(&ctx);