runtime: allow safely pulling logs even on TRACE log level.

Before this commit, this resulted in a packet flood, because
sending a TRACE log message to the host caused more TRACE log
messages to be emitted.

artiq/firmware/Cargo.lock

@@ -157,7 +157,7 @@ dependencies = [
  "log 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "logger_artiq 0.0.0",
  "proto 0.0.0",
- "smoltcp 0.4.0-pre (git+https://github.com/m-labs/smoltcp?rev=f76b4be)",
+ "smoltcp 0.4.0-pre (git+https://github.com/m-labs/smoltcp?rev=7e2dc1a)",
  "std_artiq 0.0.0",
 ]
 
@@ -183,7 +183,7 @@ dependencies = [
 [[package]]
 name = "smoltcp"
 version = "0.4.0-pre"
-source = "git+https://github.com/m-labs/smoltcp?rev=f76b4be#f76b4be42d5e80f33000d20979fcc8cccac7c14a"
+source = "git+https://github.com/m-labs/smoltcp?rev=7e2dc1a#7e2dc1a6d67278cb68f5e03f0ac21d58e85c92f7"
 dependencies = [
  "byteorder 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -221,7 +221,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum log_buffer 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "ec57723b84bbe7bdf76aa93169c9b59e67473317c6de3a83cb2a0f8ccb2aa493"
 "checksum managed 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)" = "61eb783b4fa77e8fa4d27ec400f97ed9168546b8b30341a120b7ba9cc6571aaf"
 "checksum rustc-cfg 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)" = "56a596b5718bf5e059d59a30af12f7f462a152de147aa462b70892849ee18704"
-"checksum smoltcp 0.4.0-pre (git+https://github.com/m-labs/smoltcp?rev=f76b4be)" = "<none>"
+"checksum smoltcp 0.4.0-pre (git+https://github.com/m-labs/smoltcp?rev=7e2dc1a)" = "<none>"
 "checksum walkdir 1.0.3 (registry+https://github.com/rust-lang/crates.io-index)" = "dd7c16466ecc507c7cb5988db03e6eab4aaeab89a5c37a29251fcfd3ac9b7afe"
 "checksum winapi 0.2.8 (registry+https://github.com/rust-lang/crates.io-index)" = "167dc9d6949a9b857f3451275e911c3f44255842c1f7a76f33c55103a909087a"
 "checksum winapi-build 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "2d315eee3b34aca4797b2da6b13ed88266e6d612562a0c46390af8299fc699bc"

artiq/firmware/runtime/Cargo.toml

@@ -32,6 +32,6 @@ features = ["mem"]
 
 [dependencies.smoltcp]
 git = "https://github.com/m-labs/smoltcp"
-rev = "f76b4be"
+rev = "7e2dc1a"
 default-features = false
 features = ["alloc", "collections", "log"]#, "verbose"]

artiq/firmware/runtime/mgmt.rs

@@ -1,4 +1,5 @@
-use std::io::{self, Read};
+use std::io::{self, Read, Write};
+use log::LogLevelFilter;
 use logger_artiq::BufferLogger;
 use sched::Io;
 use sched::{TcpListener, TcpStream};
@@ -43,10 +44,25 @@ fn worker(io: &Io, stream: &mut TcpStream) -> io::Result<()> {
                     io.until(|| BufferLogger::with(|logger| !logger.is_empty()))?;
 
                     BufferLogger::with(|logger| {
-                        match logger.extract(|log| stream.write_string(log)) {
+                        let log_level = logger.max_log_level();
-                            Ok(()) => Ok(logger.clear()),
+                        logger.extract(|log| {
-                            Err(e) => Err(e)
+                            stream.write_string(log)?;
-                        }
+
+                            if log_level == LogLevelFilter::Trace {
+                                // Hold exclusive access over the logger until we get positive
+                                // acknowledgement; otherwise we get an infinite loop of network
+                                // trace messages being transmitted and causing more network
+                                // trace messages to be emitted.
+                                //
+                                // Any messages unrelated to this management socket that arrive
+                                // while it is flushed are lost, but such is life.
+                                stream.flush()
+                            } else {
+                                Ok(())
+                            }
+                        })?;
+
+                        Ok(logger.clear()) as io::Result<()>
                     })?;
                 }
             },

artiq/firmware/runtime/sched.rs

@@ -528,8 +528,12 @@ impl<'a> Write for TcpStream<'a> {
     }
 
     fn flush(&mut self) -> Result<()> {
-        // smoltcp always sends all available data when it's possible; nothing to do
+        until!(self, TcpSocketLower, |s|  s.send_queue() == 0 || !s.may_send())?;
-        Ok(())
+        if self.as_lower().send_queue() == 0 {
+            Ok(())
+        } else {
+            Err(Error::new(ErrorKind::ConnectionAborted, "connection aborted"))
+        }
     }
 }