Re: [PATCH] host/rootfs: add mount-userdata command

[Demi Marie Obenour <demiobenour@gmail.com>]

[-- Attachment #1.1.1: Type: text/plain, Size: 7306 bytes --]

On 12/12/25 16:48, Alyssa Ross wrote:
> We shouldn't leave it to the user to manually mount user data
> partitions.  We want to ensure restrictive mount flags are set, and be
> able to do other operations around the mounting.  It's also nice to
> have a single place where all user data partitions can be mounted.
> I've taken inspiration from the FHS in using /media for this.

Yay!  I kept doing this manually and it was annoying.

> Signed-off-by: Alyssa Ross <hi@alyssa.is>
> ---
>  .../development/persistent-storage.adoc       | 19 ++++++++++-----
>  .../using-spectrum/creating-custom-vms.adoc   |  5 ++--
>  .../using-spectrum/vm-file-access.adoc        |  4 ++--
>  host/rootfs/Makefile                          |  2 +-
>  host/rootfs/file-list.mk                      |  1 +
>  host/rootfs/image/etc/fstab                   | 11 +++++----
>  host/rootfs/image/usr/bin/mount-userdata      | 24 +++++++++++++++++++
>  7 files changed, 50 insertions(+), 16 deletions(-)
>  create mode 100755 host/rootfs/image/usr/bin/mount-userdata
> 
> diff --git a/Documentation/development/persistent-storage.adoc b/Documentation/development/persistent-storage.adoc
> index 12426b46..c4bcc163 100644
> --- a/Documentation/development/persistent-storage.adoc
> +++ b/Documentation/development/persistent-storage.adoc
> @@ -2,7 +2,7 @@
>  :page-parent: Development
>  :page-nav_order: 2
>  
> -// SPDX-FileCopyrightText: 2024 Alyssa Ross <hi@alyssa.is>
> +// SPDX-FileCopyrightText: 2024-2025 Alyssa Ross <hi@alyssa.is>
>  // SPDX-License-Identifier: GFDL-1.3-no-invariants-or-later OR CC-BY-SA-4.0
>  
>  Spectrum's root filesystem is immutable, so if you want to be able to
> @@ -10,8 +10,15 @@ persist data between sessions, you'll need to create a persistent
>  storage partition.  Spectrum comes with `cryptsetup`, and in future is
>  likely to assume that btrfs-specific features are available.
>  
> -Conventionally, the persistent storage partition is mounted on /ext
> -after booting.  It's not mounted automatically, because generally the
> -partition should be encrypted, meaning a key has to be supplied to
> -mount it anyway, and because there might be multiple persistent data
> -partitions to choose from.
> +Persistent storage can be mounted as follows:
> +
> +[source,shell]
> +----
> +cryptsetup open /dev/sda1 userdata
> +mount-userdata /dev/mapper/userdata
> +----
> +
> +It's not mounted automatically, because generally the partition should
> +be encrypted, meaning a key has to be supplied to mount it anyway, and
> +because there might be multiple persistent data partitions to choose
> +from.
> diff --git a/Documentation/using-spectrum/creating-custom-vms.adoc b/Documentation/using-spectrum/creating-custom-vms.adoc
> index a397ac50..1eca7f36 100644
> --- a/Documentation/using-spectrum/creating-custom-vms.adoc
> +++ b/Documentation/using-spectrum/creating-custom-vms.adoc
> @@ -13,8 +13,9 @@ configurations are directories under a dedicated parent directory, and
>  the name of each configuration directory determines the name of
>  the VM.  After mounting the persistent storage partition, the
>  configured VMs can be made available by running `vm-import user
> -/ext/vms`, replacing /ext/vms with the directory containing the VM
> -definitions.
> +/media/4e43cdc2-82b2-4d94-8a90-b6c6189312d2/vms`, replacing
> +/media/4e43cdc2-82b2-4d94-8a90-b6c6189312d2/vms with the directory
> +containing the VM definitions.
>  
>  The directory can contain the following files:
>  
> diff --git a/Documentation/using-spectrum/vm-file-access.adoc b/Documentation/using-spectrum/vm-file-access.adoc
> index 1b4fe9a5..a079cfe8 100644
> --- a/Documentation/using-spectrum/vm-file-access.adoc
> +++ b/Documentation/using-spectrum/vm-file-access.adoc
> @@ -48,7 +48,7 @@ can be bind-mounted into it:
>  +
>  [listing]
>  [source,shell]
> -echo "Hello, world!" > /ext/example.txt
> +echo "Hello, world!" > /media/4e43cdc2-82b2-4d94-8a90-b6c6189312d2/example.txt
>  
>  2. Create an empty file to bind mount over:
>  +
> @@ -60,5 +60,5 @@ touch /run/vm/by-name/user.appvm-example/fs/example.txt
>  +
>  [listing]
>  [source,shell]
> -mount --rbind /ext/example.txt /run/vm/by-name/user.appvm-example/fs/example.txt
> +mount --rbind /media/4e43cdc2-82b2-4d94-8a90-b6c6189312d2/example.txt /run/vm/by-name/user.appvm-example/fs/example.txt
>  ====
> diff --git a/host/rootfs/Makefile b/host/rootfs/Makefile
> index 7bec1259..211fb5dd 100644
> --- a/host/rootfs/Makefile
> +++ b/host/rootfs/Makefile
> @@ -33,8 +33,8 @@ DIRS = \
>  	etc/s6-linux-init/run-image/user \
>  	etc/s6-linux-init/run-image/vm/by-id \
>  	etc/s6-linux-init/run-image/vm/by-name \
> -	ext \
>  	home \
> +	media \
>  	proc \
>  	run \
>  	sys \
> diff --git a/host/rootfs/file-list.mk b/host/rootfs/file-list.mk
> index f69775d2..6bf40ff8 100644
> --- a/host/rootfs/file-list.mk
> +++ b/host/rootfs/file-list.mk
> @@ -56,6 +56,7 @@ FILES = \
>  	image/etc/xdg/weston/weston.ini \
>  	image/usr/bin/assign-devices \
>  	image/usr/bin/create-vm-dependencies \
> +	image/usr/bin/mount-userdata \
>  	image/usr/bin/root-terminal \
>  	image/usr/bin/run-appimage \
>  	image/usr/bin/run-flatpak \
> diff --git a/host/rootfs/image/etc/fstab b/host/rootfs/image/etc/fstab
> index 5c23a374..18bb5e45 100644
> --- a/host/rootfs/image/etc/fstab
> +++ b/host/rootfs/image/etc/fstab
> @@ -1,7 +1,8 @@
>  # SPDX-License-Identifier: CC0-1.0
>  # SPDX-FileCopyrightText: 2020-2021, 2025 Alyssa Ross <hi@alyssa.is>
> -proc	/proc		proc	nosuid,nodev,noexec		0	0
> -devpts	/dev/pts	devpts	nosuid,noexec,gid=5,mode=620	0	0
> -tmpfs	/dev/shm	tmpfs	nosuid,nodev			0	0
> -sysfs	/sys		sysfs	nosuid,nodev,noexec		0	0
> -tmpfs	/tmp		tmpfs	nosuid,nodev			0	0
> +proc	/proc		proc	nosuid,nodev,noexec				0	0
> +devpts	/dev/pts	devpts	nosuid,noexec,gid=5,mode=620			0	0
> +tmpfs	/dev/shm	tmpfs	nosuid,nodev					0	0
> +tmpfs	/media		tmpfs	nosuid,nodev,noexec,nosymfollow,mode=755	0	0
> +sysfs	/sys		sysfs	nosuid,nodev,noexec				0	0
> +tmpfs	/tmp		tmpfs	nosuid,nodev					0	0
> diff --git a/host/rootfs/image/usr/bin/mount-userdata b/host/rootfs/image/usr/bin/mount-userdata
> new file mode 100755
> index 00000000..e4a873c0
> --- /dev/null
> +++ b/host/rootfs/image/usr/bin/mount-userdata
> @@ -0,0 +1,24 @@
> +#!/bin/execlineb -W
> +# SPDX-License-Identifier: EUPL-1.2+
> +# SPDX-FileCopyrightText: 2025 Alyssa Ross <hi@alyssa.is>
> +
> +backtick -D "" uuid {
> +  importas -Siu 1
> +  blkid -o value -s UUID $1

Missing "--"?

> +}
> +
> +multisubstitute {
> +  importas -Siu 0
> +  importas -Siu 1
> +  importas -Siu uuid
> +}
> +
> +case $uuid {
> +  "" {
> +    fdmove -c 1 2
> +    printf "%s: '%s' does not have a UUID\n" $0 $1
> +  }
> +}
> +
> +if { mount -m -o nosuid,nodev,noexec,nosymfollow -- $1 /media/${uuid} }
> +printf "%s\n" /media/${uuid}

Do we really want a mode of 0755?  Also, I believe Spectrum should
use noatime.  This avoids a burst of unsharing of snapshots due to
atime updates.

Should this use ‘-t btrfs’?  I thought Spectrum assumed this.

> base-commit: 1afc3a7042ee1c40b6d2e564219be31ea8f1017f


-- 
Sincerely,
Demi Marie Obenour (she/her/hers)

[-- Attachment #1.1.2: OpenPGP public key --]
[-- Type: application/pgp-keys, Size: 7253 bytes --]

[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 833 bytes --]