Subject: [bug#51878] [PATCH v2] installer: Rework installation device detection

From: Josselin Poiret <[email-masked]>
Date: Tue, 23 Nov 2021 22:19:09 +0000

Hello,

You're right, I didn't take CDs into account.  Here is a new version
which compares the device path itself to the --root argument as well,
which is the case for CDs.  I checked both iso9660 and qcow2 in qemu,
and both only list other devices.

I didn't quite get your comment about filtering the `(devices)` list.
In both cases, we use `remove`, but here I've factored out the predicate
used for it.

Best,
Josselin

-- >8 --
* gnu/installer/parted.scm (installation-device): Remove it.
* gnu/installer/parted.scm (installer-root-partition-path): Add it.
* gnu/installer/parted.scm (non-install-devices): Add
installation-device? predicate.
---
 gnu/installer/parted.scm | 53 +++++++++++++++++++++++-----------------
 1 file changed, 30 insertions(+), 23 deletions(-)

diff --git a/gnu/installer/parted.scm b/gnu/installer/parted.scm
index 00de0a30fa..f665e67b35 100644
--- a/gnu/installer/parted.scm
+++ b/gnu/installer/parted.scm
@@ -26,6 +26,7 @@ (define-module (gnu installer parted)
   #:use-module ((gnu build file-systems)
                 #:select (canonicalize-device-spec
                           find-partition-by-label
+                          find-partition-by-uuid
                           read-partition-uuid
                           read-luks-partition-uuid))
   #:use-module ((gnu build linux-boot)
@@ -345,35 +346,41 @@ (define (remove-logical-devices)
   (with-null-output-ports
    (invoke "dmsetup" "remove_all")))
 
-(define (installation-device)
-  "Return the installation device path."
+(define (installer-root-partition-path)
+  "Return the root partition path, or #f if it could not be detected."
   (let* ((cmdline (linux-command-line))
          (root (find-long-option "--root" cmdline)))
     (and root
-         (canonicalize-device-spec (uuid root)))))
+         (or (and (access? root F_OK) root)
+             (find-partition-by-label root)
+             (and=> (uuid root)
+                    find-partition-by-uuid)))))
 
 (define (non-install-devices)
   "Return all the available devices, except the install device."
-  (define (read-only? device)
-    (dynamic-wind
-    (lambda ()
-      (device-open device))
-    (lambda ()
-      (device-read-only? device))
-    (lambda ()
-      (device-close device))))
-
-  ;; If parted reports that a device is read-only it is probably the
-  ;; installation device. However, as this detection does not always work,
-  ;; compare the device path to the installation device path read from the
-  ;; command line.
-  (let ((install-device (installation-device)))
-    (remove (lambda (device)
-              (let ((file-name (device-path device)))
-                (or (read-only? device)
-                    (and install-device
-                         (string=? file-name install-device)))))
-            (devices))))
+
+  (define the-installer-root-partition-path
+    (installer-root-partition-path))
+
+  ;; Read partition table of device and compare each path to the one
+  ;; we're booting from to determine if it is the installation
+  ;; device.
+  (define (installation-device? device)
+    (or (string=? the-installer-root-partition-path
+                  (device-path device))
+        (let ((disk (disk-new device)))
+          (and disk
+               (let loop ((partition #f))
+                 (let ((next-partition (disk-next-partition disk
+                                                            #:partition
+                                                            partition)))
+                   (and next-partition
+                        (or (string=? the-installer-root-partition-path
+                                      (partition-get-path
+                                       next-partition))
+                            (loop next-partition)))))))))
+
+  (remove installation-device? (devices)))
 
 
 ;;
-- 
2.33.1