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processes: Gracefully handle daemons without clients.

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Fixes <https://bugs.gnu.org/34716>.
Reported by Mark H Weaver <mhw@netris.org>.

The problem could be reproduced by running, on one hand:

  sh -c 'exec -a guix-daemon sleep 777'

and on the other hand:

  guix processes

If there is no process with PID 777, 'guix processes' would barf as it
stumbles upon a <daemon-session> record whose client is #f.

* guix/scripts/processes.scm (daemon-sessions)[child-process->session]:
New procedure, with lambda formerly passed to 'map'.  Handle #f returns
from 'lookup-process'.
Call 'child-process->session' within 'filter-map', not just 'map'.
This commit is contained in:
Ludovic Courtès 2019-04-29 21:42:04 +02:00
parent c21d912a02
commit c20d4cac1f
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guix/scripts/processes.scm
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@ -158,15 +158,22 @@ active sessions, and the master 'guix-daemon' process."
(= pid (process-parent-id process))))
processes))
(values (map (lambda (process)
(match (process-command process)
((argv0 (= string->number client) _ ...)
(let ((files (process-open-files process)))
(daemon-session process
(lookup-process client)
(lookup-children (process-id process))
(filter lock-file? files))))))
children)
(define (child-process->session process)
(match (process-command process)
((argv0 (= string->number client) _ ...)
(let ((files (process-open-files process))
(client (lookup-process client)))
;; After a client has died, there's a window during which its
;; corresponding 'guix-daemon' process is still alive, in which
;; case 'lookup-process' returns #f. In that case ignore the
;; session.
(and client
(daemon-session process client
(lookup-children
(process-id process))
(filter lock-file? files)))))))
(values (filter-map child-process->session children)
master)))
(define (daemon-session->recutils session port)