bug#53541: [installer] backtrace during fresh Guix System install after during formatting

[Mathieu Othacehe]

Hey,

> so the disk partition table is updated because we move from 4 to 2
> partitions. Could it be possible that during a brief period of time the
> /dev/nvme0n1p1 file disappears then re-appears?

Looks like that's what happening. I'm not able to reproduce it on a
VM. I guess that's because my hardware is slower.

Anyway having a few retries of read-partition-uuid fixes it for me. This
is a bit dirty but that's how we usually deal with that kind of
problems. A patch is attached.

Running those tests I experienced a segmentation fault in libparted and
then in libblkid, but that's another story. I'll open a ticket about
that later on.

Thanks,

Mathieu

>From 4407374ff4087772bd8226824cf4883537752f01 Mon Sep 17 00:00:00 2001
From: Mathieu Othacehe <othacehe@gnu.org>
Date: Sat, 22 Oct 2022 22:27:57 +0200
Subject: [PATCH 1/1] installer: parted: Retry failing read-partition-uuid
 call.

Fixes: <https://issues.guix.gnu.org/53541>.

* gnu/installer/parted.scm (read-partition-uuid/retry): New procedure.
(check-user-partitions): Use it.
---
 gnu/installer/parted.scm | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/gnu/installer/parted.scm b/gnu/installer/parted.scm
index fcc936a391..82375d29e3 100644
--- a/gnu/installer/parted.scm
+++ b/gnu/installer/parted.scm
@@ -319,6 +319,25 @@ (define (find-user-partition-by-parted-object 
user-partitions
                   partition))
         user-partitions))
 
+(define (read-partition-uuid/retry file-name)
+  "Call READ-PARTITION-UUID with 5 retries spaced by 1 second.  This is useful
+if the partition table is updated by the kernel at the time this function is
+called, causing the underlying /dev to be absent."
+  (define max-retries 5)
+
+  (let loop ((retry max-retries))
+    (catch #t
+      (lambda ()
+        (read-partition-uuid file-name))
+      (lambda _
+        (if (> retry 0)
+            (begin
+              (sleep 1)
+              (loop (- retry 1)))
+            (error
+             (format #f (G_ "Could not open ~a after ~a retries~%.")
+                     file-name max-retries)))))))
+
 
 ;;
 ;; Devices
@@ -1108,7 +1127,7 @@ (define (check-uuid)
                (need-formatting?
                 (user-partition-need-formatting? user-partition)))
            (or need-formatting?
-               (read-partition-uuid file-name)
+               (read-partition-uuid/retry file-name)
                (raise
                 (condition
                  (&cannot-read-uuid
-- 
2.38.0