mzan

Sometime #Guile and #Guix error messages are confusing. I will collect here some of them, as case study. Don't get me wrong: Guile is wonderful and it is OSS.

Guile limitations

• Racket uses contracts, so the error is signaled at the exact point where something of unexpected is happening, while in Guile one should travel the stack-trace for identifying the real source of the problem;
• Typed Racket recognizes many errors at compile-time, while in Guile mainly at run-time;
• CL has more type annotations in libraries, and (at least in SBCL) they are signaled as warnings during compilation;
• CL run-time uses a stack, while Scheme has continuations, so sometime a proper stack-trace is missing;
• in CL you can inspect also the parameters passed to functions, so it is easier figuring out the problem;

Guix system reconfigure

sudo guix system reconfigure ...

mnt/bcachefs/home/mzan/lavoro/admin/guix/think/config-nonguix.scm:439:10: error: device '/dev/sdb:/dev/sdc:/dev/sdd' not found: No such file or directory
error: Recipe `system-reconfigure` failed with exit code 1

The signaled problem is in this part of the configuration

          (file-system
             (mount-point "/mnt/bcachefs")
             (device "/dev/sdb:/dev/sdc:/dev/sdd")
             (type "bcachefs"))

Guix does not yet support a bcachefs-like device format. I need to extend Guix. The error message is informative enough for end-users, but it is not optimal for developers wanting to improve Guix, because there is no stack-trace informing in which point Guix is stuck.

Solution

I added a unique fixed error-code to generated errors, so the exact point of the error can be found quickly. For example

/mnt/bcachefs/home/mzan/lavoro/admin/guix/think/config-nonguix.scm:439:10: error:  #8658 device '/dev/sdb:/dev/sdc:/dev/sdd' not found: No such file or directory
error: Recipe `system-reconfigure` failed with exit code 1

In this way the error messages will be still nice for end-users (they don't see an ugly stack-trace), but useful also for developers.

Guix system reconfigure

After extending the source code, I tried to reconfigure

 sudo -E ./pre-inst-env guix system reconfigure /home/mzan/lavoro/admin/guix/think/config-nonguix.scm
--keep-going

I obtain this

Backtrace:
In guix/ui.scm:
  2293:10 19 (run-guix-command _ . _)
In ice-9/boot-9.scm:
  1752:10 18 (with-exception-handler _ _ #:unwind? _ # _)
    152:2 17 (with-fluid* _ _ _)
In guix/status.scm:
    839:4 16 (call-with-status-report _ _)
In ice-9/eval.scm:
    619:8 15 (_ #(#(#(#(#(#(#(#(#(#(#(…) …) …) …) …) …) …) …) …) …) …))
In ice-9/boot-9.scm:
  1752:10 14 (with-exception-handler _ _ #:unwind? _ # _)
In guix/store.scm:
   689:37 13 (thunk)
   1330:8 12 (call-with-build-handler #<procedure 7f7ea628ed80 at g…> …)
  2210:25 11 (run-with-store #<store-connection 256.100 7f7ea61700f0> …)
In ice-9/eval.scm:
   191:27 10 (_ #(#(#<directory (guix scripts system) 7f7ebac0…> …) …))
    619:8  9 (_ #(#(#(#<directory (guix scripts system) 7f7eb…>) …) …))
    619:8  8 (_ #(#(#(#<directory (guix scripts system) 7f7eb…>) …) …))
    619:8  7 (_ #(#(#(#<directory (guix scripts system) 7f7eb…>) …) …))
In srfi/srfi-1.scm:
    634:9  6 (for-each #<procedure 7f7ea4380ac0 at ice-9/eval.scm:3…> …)
In ice-9/eval.scm:
   298:42  5 (_ #(#(#<directory (guix scripts system) 7f7ebac0…> …) …))
    159:9  4 (_ #(#(#<directory (guix scripts system) 7f7ebac0…> …) …))
   223:20  3 (proc #(#(#<directory (guix scripts system) 7f7eb…> …) …))
In unknown file:
           2 (%resolve-variable (7 . devices) #<directory (guix scri…>)
In ice-9/boot-9.scm:
  1685:16  1 (raise-exception _ #:continuable? _)
  1685:16  0 (raise-exception _ #:continuable? _)

ice-9/boot-9.scm:1685:16: In procedure raise-exception:
error: devices: unbound variable
error: Recipe `system-reconfigure` failed with exit code 1

The file and position of the error is missing. Also the stack trace is rather incomplete and there are no useful names for functions. I had to check the devices variable name in last modified source-code. I found it, but this way of proceeding is far from optimal, and rather stressful.

Solution

Probably this needs many improvements to the Guile source code.

Guix reboot

I rebooted the computer with the new settings. There were an error in the code, and the machine was blocked:

In this case I have only praises for Guix: – the error message reports the exact source-code file and position; – I easily rebooted using old profiles, and fixed the bug;

gexp errors

I patched Guix, for recognizing bcachefs multi-device (e.g. “/dev/sda:/dev/sdb:/dev/sdc”).

 ./pre-inst-env guix deploy /home/mzan/lavoro/admin/guix/buildbart/deploy.scm

I obtained this confusing error message

The following 1 machine will be deployed:
  buildbart

guix deploy: deploying to buildbart...
guix deploy: warning: <machine-ssh-configuration> without a 'host-key' is deprecated
guix deploy: sending 0 store items (0 MiB) to 'buildbart'...
Backtrace:
In ice-9/boot-9.scm:
  1752:10 19 (with-exception-handler _ _ #:unwind? _ # _)
In guix/store.scm:
   689:37 18 (thunk)
   1330:8 17 (call-with-build-handler _ _)
   1330:8 16 (call-with-build-handler #<procedure 7f0503a86630 at g…> …)
In guix/scripts/deploy.scm:
   284:23 15 (_)
In guix/store.scm:
  1437:13 14 (map/accumulate-builds #<store-connection 256.100 7f05…> …)
  1412:11 13 (map/accumulate-builds #<store-connection 256.100 7f05…> …)
   1330:8 12 (call-with-build-handler #<procedure 7f0505de66c0 at g…> …)
In ice-9/boot-9.scm:
  1752:10 11 (with-exception-handler _ _ #:unwind? _ # _)
In guix/scripts/deploy.scm:
    166:6 10 (_)
In guix/store.scm:
  2210:25  9 (run-with-store #<store-connection 256.100 7f050369dd70> …)
In unknown file:
           8 (_ #<procedure 7f05038af060 at ice-9/eval.scm:330:13 ()> …)
In ice-9/eval.scm:
   191:27  7 (_ #(#(#<directory (gnu machine ssh) 7f0505887e60> #) …))
    619:8  6 (_ #(#(#(#<directory (gnu machine ssh) 7f05058…> …) …) …))
In srfi/srfi-1.scm:
   650:11  5 (for-each #<procedure 7f0511893cc0 at ice-9/eval.scm:3…> …)
In ice-9/eval.scm:
   245:16  4 (_ #(#(#<directory (gnu machine ssh) 7f0505887e60> #) #))
In srfi/srfi-1.scm:
   876:18  3 (every1 #<procedure number? (_)> _)
In ice-9/boot-9.scm:
  1685:16  2 (raise-exception _ #:continuable? _)
  1685:16  1 (raise-exception _ #:continuable? _)
  1685:16  0 (raise-exception _ #:continuable? _)

ice-9/boot-9.scm:1685:16: In procedure raise-exception:
In procedure cdr: Wrong type argument in position 1 (expecting pair): #f
mzan@think ~/lavoro/admin/guix/custom-guix-repo$

Probably it is a stupid error, and in this case a static type-checking could help, because it seems an error in the params sent to a function. But, for discovering the error in Guile, I need to test the code, figuring out where is the problem.

The error message lacks some info about the correct position on sorce-code, because it is a thunk of code (i.e. a gexp) executed on the remote machine. To be fair, sometime Guix is able to indicate the correct position in the source-code of gexp, because it can add this meta-info to gexp thunks. So I'm doing some FUD.

Analysis of Guix code

The Guix command line entry point is guix/ui/guix-main. It reads the settings passed by my command-line ./pre-inst-env guix .... If I want to launch a debugging Guile session, I need to pass these params in some way.

• from a shell, I asked the position of guix with ./pre-inst-env which guix. In my case it is /mnt/bcachefs/srv/git/custom-guix-repo/scripts/guix
• I loaded guix/ui.scm in Geiser, the Emacs Guile module
• I entered in the module with ,module guix ui
• I called the guix deploy function with (guix-main "/mnt/bcachefs/srv/git/custom-guix-repo/scripts/guix" "deploy" "/home/mzan/lavoro/admin/guix/buildbart/deploy.scm")
• I obtain the error message ice-9/boot-9.scm:1685:16: In procedure raise-exception: In procedure port-column: Wrong type argument in position 1: #<closed: string 7efc1922e1c0>
• I can play with the Guile debug shell, for inspecting better the source of the error
• I'm not an expert but the CL SBCL debug session seems a lot more interactive, and I can explore better. In Guile it is a lot less fun.

Sadly the obtained error is different from the error executing on the command line, using ./pre-inst-env, and it starts to becoming frustrating

Debugging using test code

I created simplified version of the code, for isolating the error, and I called from Geiser, using

(guix-main "/mnt/bcachefs/srv/git/custom-guix-repo/scripts/guix" "deploy" "/home/mzan/lavoro/admin/guix/buildbart/deploy.scm")

So instead of an interactive process, like in CL, an iterative one: – save the code; – simplify the code; – create test code; – print some results; – isolate the error; – backport the fix to the real saved code;

This process is far from ideal.

Debugging of code to execute as root

The Guile code used in the initrd phase can call protected files, e.g. for reading the bcachefs super-block. So I cannot execute it inside a Geiser process.

I created this file, containing code to test. It must be safe code, because it will run as root:

; t.scm

(use-modules (gnu build file-systems))

(canonicalize-device-spec "/dev/sda:/dev/sda1:/dev/sdb:/dev/sdc")

and I call it with

$ ./pre-inst-env sudo -E guix repl t.scm

obtaining these debug mesages

specs: ("/dev/sda" "/dev/sda1" "/dev/sdb" "/dev/sdc")

 "/dev/sda" #f #f
 "/dev/sda1" #f #vu8(218 217 209 178 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 193 184 1 212 171 134 78 98 176 210 248 239 125 66 72 121 0 0 1 0 0 0 0 0 1 0 0 0 0 0 0 0 95 66 72 82 102 83 95 77 165 226 1 0 0 0 0 0 0 192 28 33 35 0 0 0 0 64 135 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 160 56 58 0 0 0 0 208 76 18 35 0 0 0 6 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 16 0 0 0 64 0 0 0 64 0 0 0 16 0 0 129 0 0 0 177 220 1 0 0 0 0 0 0 0 0 0 0 0 0 0 3 0 0 0 0 0 0
[...]
 0 0 0 0 0 0 0 0 0 0 0 0 0 0)

 "/dev/sdb" #f #f
 "/dev/sdc" #f #f
 valid-specs: ()
Backtrace:
           3 (primitive-load "/mnt/bcachefs/home/mzan/lavoro/admin/c…")
In ice-9/eval.scm:
    619:8  2 (_ #(#(#(#(#<directory (gnu build file-syst…> …) …) …) …))
In ice-9/boot-9.scm:
   2007:7  1 (error _ . _)
  1685:16  0 (raise-exception _ #:continuable? _)

ice-9/boot-9.scm:1685:16: In procedure raise-exception:
failed to resolve multi-device  "/dev/sda:/dev/sda1:/dev/sdb:/dev/sdc"

This message contains also debug info I manually generated using (format #t ...) code.

HashTags

• #GuixDev series
• #Guix