bug#52919: Hidden "disk-image-rw" files aren't deleted after use, filling $tmpdir

[Mathieu Othacehe <othacehe@gnu.org>]

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Hey,

> Hmm.  Can we keep “image” persistent by default, and make ‘vm’ volatile
> by default?  That way, ‘--volatile’ would only make sense for ‘image’,
> and ‘--persistent’ would only make sense for ‘vm’.  (So we’d be adding
> just one option: ‘--persistent’.)
>
> WDYT?

I'm not fan of adding antithetic options: --x and --no-x. There's an
attached patch introducing --volatile-image and --persistent-vm options,
and documenting them. It's maybe not that bad after all.

> I would still ensure they have a name like “guix-image-$USER-XXX”, where
> XXX is the store file basename.

Sure.

Thanks,

Mathieu

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From b0c84a411f9f23f4f1a4155ba5efa68cac9004a2 Mon Sep 17 00:00:00 2001
From: Mathieu Othacehe <othacehe@gnu.org>
Date: Thu, 13 Jan 2022 11:35:40 +0100
Subject: [PATCH 1/2] scripts: system: Rationalize persistency.

Make sure that the images are created with a non volatile root by default and
the vm are created with a volatile root by default. Break the --volatile
option into --volatile-image and --persistent-vm options.

* guix/scripts/system.scm (perform-action): Turn volatile? argument into
volatile-vm-root?.
(show-help): Introduce --volatile-image and --persistent-vm options instead of
--volatile.
(%default-options): Adapt it.
(%options): Handle those options.
(process-action): Honor them.
* doc/guix.texi (Invoking guix system): Adapt it accordingly.
---
 doc/guix.texi           | 15 ++++++++++-----
 guix/scripts/system.scm | 25 +++++++++++++++++--------
 2 files changed, 27 insertions(+), 13 deletions(-)

diff --git a/doc/guix.texi b/doc/guix.texi
index bc289bad7b..9f763bcfa7 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -35152,6 +35152,11 @@ $ $(guix system vm my-config.scm) -m 1024 -smp 2 -nic user,model=virtio-net-pci
 
 The VM shares its store with the host system.
 
+By default, the root file system of the VM is mounted volatile; the
+@option{--persistent-vm} option can be provided to make it persistent
+instead.  In that case, the VM disk-image file will be copied from the
+store to the @env{TMPDIR} directory to make it writable.
+
 Additional file systems can be shared between the host and the VM using
 the @option{--share} and @option{--expose} command-line options: the former
 specifies a directory to be shared with write access, while the latter
@@ -35189,14 +35194,14 @@ QEMU monitor and the VM.
 @cindex Creating system images in various formats
 @item image
 @cindex image, creating disk images
-The @code{image} command can produce various image types.  The
-image type can be selected using the @option{--image-type} option.  It
+The @code{image} command can produce various image types.  The image
+type can be selected using the @option{--image-type} option.  It
 defaults to @code{efi-raw}.  When its value is @code{iso9660}, the
 @option{--label} option can be used to specify a volume ID with
 @code{image}.  By default, the root file system of a disk image is
-mounted non-volatile; the @option{--volatile} option can be provided to
-make it volatile instead.  When using @code{image}, the bootloader
-installed on the generated image is taken from the provided
+mounted non-volatile; the @option{--volatile-image} option can be
+provided to make it volatile instead.  When using @code{image}, the
+bootloader installed on the generated image is taken from the provided
 @code{operating-system} definition.  The following example demonstrates
 how to generate an image that uses the @code{grub-efi-bootloader}
 bootloader and boot it with QEMU:
diff --git a/guix/scripts/system.scm b/guix/scripts/system.scm
index 98e788c657..3ca5592e34 100644
--- a/guix/scripts/system.scm
+++ b/guix/scripts/system.scm
@@ -772,7 +772,7 @@ (define* (perform-action action image
                          dry-run? derivations-only?
                          use-substitutes? target
                          full-boot?
-                         volatile?
+                         volatile-vm-root?
                          (graphic? #t)
                          container-shared-network?
                          (mappings '())
@@ -827,7 +827,8 @@ (define bootcfg
   (mlet* %store-monad
       ((sys       (system-derivation-for-action image action
                                                 #:full-boot? full-boot?
-                                                #:volatile? volatile?
+                                                #:volatile?
+                                                volatile-vm-root?
                                                 #:graphic? graphic?
                                                 #:container-shared-network? container-shared-network?
                                                 #:mappings mappings))
@@ -997,7 +998,9 @@ (define (show-help)
   (display (G_ "
       --no-bootloader    for 'init', do not install a bootloader"))
   (display (G_ "
-      --volatile         for 'image', make the root file system volatile"))
+      --volatile-image   for 'image', make the root file system volatile"))
+  (display (G_ "
+      --persistent-vm    for 'vm', make the root file system persistent"))
   (display (G_ "
       --label=LABEL      for 'image', label disk image with LABEL"))
   (display (G_ "
@@ -1078,9 +1081,12 @@ (define %options
          (option '("no-bootloader" "no-grub") #f #f
                  (lambda (opt name arg result)
                    (alist-cons 'install-bootloader? #f result)))
-         (option '("volatile") #f #f
+         (option '("volatile-image") #f #f
+                 (lambda (opt name arg result)
+                   (alist-cons 'volatile-image-root? #t result)))
+         (option '("persistent-vm") #f #f
                  (lambda (opt name arg result)
-                   (alist-cons 'volatile-root? #t result)))
+                   (alist-cons 'volatile-vm-root? #f result)))
          (option '("label") #t #f
                  (lambda (opt name arg result)
                    (alist-cons 'label arg result)))
@@ -1149,7 +1155,8 @@ (define %default-options
     (image-size . guess)
     (install-bootloader? . #t)
     (label . #f)
-    (volatile-root? . #f)
+    (volatile-image-root? . #f)
+    (volatile-vm-root? . #t)
     (graph-backend . "graphviz")))
 
 (define (verbosity-level opts)
@@ -1219,7 +1226,8 @@ (define save-provenance?
                                            ((docker-image) docker-image-type)
                                            (else image-type)))
                             (image-size (assoc-ref opts 'image-size))
-                            (volatile?  (assoc-ref opts 'volatile-root?))
+                            (volatile?
+                             (assoc-ref opts 'volatile-image-root?))
                             (shared-network?
                                (assoc-ref opts 'container-shared-network?))
                             (base-image (if (operating-system? obj)
@@ -1279,7 +1287,8 @@ (define (graph-backend)
                                #:validate-reconfigure
                                (assoc-ref opts 'validate-reconfigure)
                                #:full-boot? (assoc-ref opts 'full-boot?)
-                               #:volatile? (assoc-ref opts 'volatile-root?)
+                               #:volatile-vm-root?
+                               (assoc-ref opts 'volatile-vm-root?)
                                #:graphic? (not (assoc-ref opts 'no-graphic?))
                                #:container-shared-network?
                                (assoc-ref opts 'container-shared-network?)
-- 
2.34.0