qemumonitor: fix for qemu v2.12

Must use expect now for some reason, and I only know how to make it work
nicely if the arguments come from CLI arguments instead of stdin.

Document it on a dedicated section.

Fix #29

README.adoc

@@ -228,32 +228,9 @@ https://superuser.com/questions/1087859/how-to-quit-the-qemu-monitor-when-not-us
 
 Alternative methods:
 
-* `echo quit | ./qemumonitor`
-* `Ctrl-A C` then `quit`
+* `quit` command on the <<qemu-monitor>>
 * `pkill qemu`
 
-Toggle between QEMU monitor and the shell:
-
-....
-Ctrl-A C
-....
-
-* http://stackoverflow.com/questions/14165158/how-to-switch-to-qemu-monitor-console-when-running-with-curses
-* https://superuser.com/questions/488263/how-to-switch-to-the-qemu-control-panel-with-nographics
-
-But doing:
-
-....
-echo quit | ./qemumonitor
-....
-
-is generally more practical since you can use host shell functionality like shell history.
-
-Getting everything to work requires careful choice of QEMU command line options:
-
-* https://stackoverflow.com/questions/49716931/how-to-run-qemu-with-nographic-and-monitor-but-still-be-able-to-send-ctrlc-to/49751144#49751144
-* https://unix.stackexchange.com/questions/167165/how-to-pass-ctrl-c-to-the-guest-when-running-qemu-with-nographic/436321#436321
-
 TODO: if you hit `Ctrl-C` several times while `arm` or `aarch64` are booting, after boot the userland shell does not show any updates when you type, this seems to be a bug on the Linux kernel v4.16: http://lists.nongnu.org/archive/html/qemu-discuss/2018-04/msg00027.html
 
 === Graphic mode
@@ -280,7 +257,7 @@ Text mode has the following limitations over graphics mode:
 `x86_64` has a VGA device enabled by default, as can be seen as:
 
 ....
-echo 'info qtree' | ./qemumonitor
+./qemumonitor info qtree
 ....
 
 and the Linux kernel picks it up through the link:https://en.wikipedia.org/wiki/Linux_framebuffer[fbdev] graphics system as can be seen from:
@@ -2898,6 +2875,12 @@ which shows:
 
 so only `1` has `myirqhandler0` attached but not `0`.
 
+The <<qemu-monitor>> also has some interrupt statistics for x86_64:
+
+....
+./qemumonitor info irq
+....
+
 TODO: properly understand how each IRQ maps to what number.
 
 ==== dummy-irq
@@ -3757,7 +3740,7 @@ and run:
 On another shell, take a snapshot:
 
 ....
-echo 'savevm my_snap_id' | ./qemumonitor
+./qemumonitor savevm my_snap_id
 ....
 
 The counting continues.
@@ -3765,7 +3748,7 @@ The counting continues.
 Restore the snapshot:
 
 ....
-echo 'loadvm my_snap_id' | ./qemumonitor
+./qemumonitor loadvm my_snap_id
 ....
 
 and the counting goes back to where we saved. This shows that CPU and memory states were reverted.
@@ -3785,7 +3768,7 @@ echo 0 >f
 Monitor:
 
 ....
-echo 'savevm my_snap_id' | ./qemumonitor
+./qemumonitor savevm my_snap_id
 ....
 
 Guest:
@@ -3797,7 +3780,7 @@ echo 1 >f
 Monitor:
 
 ....
-echo 'loadvm my_snap_id' | ./qemumonitor
+./qemumonitor loadvm my_snap_id
 ....
 
 Guest:
@@ -3965,7 +3948,7 @@ which we identify as being `edu` and `pci_min` respectively by the magic numbers
 Alternatively, we can also do use the QEMU monitor:
 
 ....
-echo 'info qtree' | ./qemumonitor
+./qemumonitor info qtree
 ....
 
 which gives:
@@ -4562,6 +4545,62 @@ The current FAQ says it is not possible to use dynamic executables: http://gem5.
 
 but I could not find how to actually use it.
 
+=== QEMU monitor
+
+The QEMU monitor is a terminal that allows you to send text commands to the QEMU VM: https://en.wikibooks.org/wiki/QEMU/Monitor
+
+Accessed it in either <<text-mode>> and <<graphic-mode>>:
+
+....
+./qemumonitor
+....
+
+or send one command such as `info qtree` and quit the monitor:
+
+....
+./qemumonitor info qtree
+....
+
+Source: link:qemumonitor[]
+
+`qemumonitor` uses the `-monitor` QEMU command line option, which makes the monitor listen from a socket.
+
+`qemumonitor` does not support input from an stdin pipe currently, see comments on the source for rationale.
+
+Alternatively, from text mode:
+
+....
+Ctrl-A C
+....
+
+and go back to the terminal with:
+
+....
+Ctrl-A C
+....
+
+* http://stackoverflow.com/questions/14165158/how-to-switch-to-qemu-monitor-console-when-running-with-curses
+* https://superuser.com/questions/488263/how-to-switch-to-the-qemu-control-panel-with-nographics
+
+And in graphic mode from the GUI:
+
+....
+Ctrl-Alt ?
+....
+
+where `?` is a digit `1`, or `2`, or, `3`, etc. depending on what else is available on the GUI: serial, parallel and frame buffer.
+
+In general, `./qemumonitor` is the best option, as it:
+
+* works on both modes
+* allows to use the host Bash history to re-run one off commands
+* allows you to search the output of commands on your host shell even when in graphic mode
+
+Getting everything to work required careful choice of QEMU command line options:
+
+* https://stackoverflow.com/questions/49716931/how-to-run-qemu-with-nographic-and-monitor-but-still-be-able-to-send-ctrlc-to/49751144#49751144
+* https://unix.stackexchange.com/questions/167165/how-to-pass-ctrl-c-to-the-guest-when-running-qemu-with-nographic/436321#436321
+
 === Debug the emulator
 
 When you start hacking QEMU or gem5, it is useful to see what is going on inside the emulator themselves.

configure

@@ -32,6 +32,7 @@ bc \
 build-essential \
 coreutils \
 cpio \
+expect \
 git \
 unzip \
 vinagre \

qemumonitor

@@ -1,5 +1,24 @@
-#!/usr/bin/env bash
-# We could also use Ctrl + Alt + 2 on the SDL GUI,
-# but that opens up a tiny window which can't scroll up or be searched.
-# And this is the only way when running in -noscreen.
-telnet localhost 45454
+#!/usr/bin/env expect
+# Ee have to use expect since QEMU 2.12: just piping commands
+# into telnet stopped working at that version.
+spawn telnet localhost 45454
+set prompt "\n(qemu) "
+expect $prompt
+if {$argc > 0} {
+  send "[concat [join $argv " "]]\r"
+  expect $prompt
+} else {
+  interact
+}
+
+# In order to treat input from stdin, we would need to differentiate between input from pipe vs terminal.
+# For bash we can do it as:
+# https://stackoverflow.com/questions/911168/how-to-detect-if-my-shell-script-is-running-through-a-pipe
+# but no one knows for Tcl:
+# https://stackoverflow.com/questions/43660612/how-to-check-if-stdin-stdout-are-connected-to-a-terminal-in-tcl
+# One option would also be to have a bash wrapper that calls this tcl script.
+# Related: https://stackoverflow.com/questions/10237872/expect-redirect-stdin
+#while {[gets stdin line] > 0} {
+  #expect $prompt
+  #send "$line\r"
+#}