main: add --syslog-tag option to crosvm

This mirrors the functionality of the `crosvm run --syslog-tag` option
that we already have; the long-term goal is to remove the run-specific
option and use the top-level argument instead, but we will keep both for
compatibility until downstream projects have migrated.

Moving the option to the top level arguments will let us initialize
logging earlier once the run option is dropped.

BUG=b:240578830
TEST=crosvm --syslog-tag TEST run bzImage # observe TEST in syslog

Change-Id: Ie7ff8dc8e43a13b11641fcefd12b40ecf339970b
Reviewed-on: https://chromium-review.googlesource.com/c/crosvm/crosvm/+/3792427
Commit-Queue: Daniel Verkamp <dverkamp@chromium.org>
Reviewed-by: Alexandre Courbot <acourbot@chromium.org>
Reviewed-by: Noah Gold <nkgold@google.com>
Tested-by: Daniel Verkamp <dverkamp@chromium.org>

src/crosvm/cmdline.rs

@@ -106,6 +106,9 @@ pub struct CrosvmCmdlineArgs {
     #[argh(option, default = r#"String::from("info")"#)]
     /// specify log level, eg "off", "error", "debug,disk=off", etc
     pub log_level: String,
+    #[argh(option, arg_name = "TAG")]
+    /// when logging to syslog, use the provided tag
+    pub syslog_tag: Option<String>,
     #[argh(switch)]
     /// disable output to syslog
     pub no_syslog: bool,

src/main.rs

@@ -507,6 +507,7 @@ fn crosvm_main() -> Result<CommandStatus> {
 
     let mut log_config = LogConfig {
         filter: &args.log_level,
+        proc_name: args.syslog_tag.unwrap_or("crosvm".to_string()),
         syslog: !args.no_syslog,
         ..Default::default()
     };