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

Demi Marie Obenour
2025-12-12T23:02:35Z

[-- 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 --]