crosvm: add debug labels to devices for improved SIGCHLD logs

Each device (Bus, Pci, Proxy, etc), gets a debug label associated with
it. When a child is spawned, the debug label for it is stored in
a map with the child's pid as the key. If a SIGCHLD is handled, this map
is used to print a more helpful message about exactly which child died.

BUG=None
TEST=run with sandboxing and a faulty child device
     check logs for message about child died
     the child should have a debug label

Change-Id: I61fbbee0a8e701249533a7a3a6a1ad48840f12e5
Reviewed-on: https://chromium-review.googlesource.com/1432835
Commit-Ready: Chih-Yang Hsia <paulhsia@chromium.org>
Tested-by: kokoro <noreply+kokoro@google.com>
Tested-by: Zach Reizner <zachr@chromium.org>
Reviewed-by: Daniel Verkamp <dverkamp@chromium.org>

1 files changed, 6 insertions, 4 deletions

diff --git a/src/linux.rs b/src/linux.rs
index 1dcedbe..4b684ca 100644
--- a/src/linux.rs
+++ b/src/linux.rs
@@ -1023,12 +1023,14 @@ fn run_control(
                 Token::ChildSignal => {
                     // Print all available siginfo structs, then exit the loop.
                     while let Some(siginfo) = sigchld_fd.read().map_err(Error::SignalFd)? {
+                        let pid = siginfo.ssi_pid;
+                        let pid_label = match linux.pid_debug_label_map.get(&pid) {
+                            Some(label) => format!("{} (pid {})", label, pid),
+                            None => format!("pid {}", pid),
+                        };
                         error!(
                             "child {} died: signo {}, status {}, code {}",
-                            siginfo.ssi_pid,
-                            siginfo.ssi_signo,
-                            siginfo.ssi_status,
-                            siginfo.ssi_code
+                            pid_label, siginfo.ssi_signo, siginfo.ssi_status, siginfo.ssi_code
                         );
                     }
                     break 'poll;