Add in the modem overlay controls #7

mrlambchop · 2025-12-04T18:53:13Z

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Copilot

Pull request overview

This PR adds a new overlay to configure Qualcomm modem support for the Tachyon device, including ModemManager configuration, rmtfs service setup, and modem partition management. The overlay is integrated into the ubuntu-common-24.04 stack.

Key changes:

New fix-qcom-modem overlay that configures ModemManager, rmtfs service, and modem partition mounts
Systemd service overrides for ModemManager and rmtfs to ensure proper initialization order and debugging
Comprehensive documentation added in CLAUDE.md describing the overlay system architecture

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 12 comments.

Show a summary per file

File	Description
stacks/ubuntu-common-24.04.json	Adds the fix-qcom-modem overlay to the build stack
overlays/fix-qcom-modem/overlay.json	Main overlay configuration defining modem setup commands
overlays/fix-qcom-modem/files/rmtfs-override.conf	Systemd override for rmtfs service configuration
overlays/fix-qcom-modem/files/fstab-entries	Filesystem mount entries for modem partitions (/persist and /firmware)
overlays/fix-qcom-modem/files/ModemManager-override.conf	Systemd override for ModemManager with debugging and dependencies
overlays/fix-qcom-modem/files/99-tachyon-ignore-at.conf	ModemManager filter to ignore specific AT command interfaces
overlays/fix-qcom-modem/create-modem-symlinks.sh	Script to create modem partition symlinks in /persist directory
CLAUDE.md	Comprehensive documentation of the overlay system, architecture, and usage

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Copilot · 2025-12-04T18:58:23Z

overlays/fix-qcom-modem/overlay.json

+      "cmd": "mkdir -p /persist/rmts"
+    },
+    {
+      "type": "chroot-cmd",
+      "cmd": "chmod 755 /persist/rmts"


Typo in directory name: rmts should be rmtfs. Same issue as line 37 - this inconsistency will cause the rmtfs service to fail.

Suggested change

"cmd": "mkdir -p /persist/rmts"

},

{

"type": "chroot-cmd",

"cmd": "chmod 755 /persist/rmts"

"cmd": "mkdir -p /persist/rmtfs"

},

{

"type": "chroot-cmd",

"cmd": "chmod 755 /persist/rmtfs"

Copilot · 2025-12-04T18:58:23Z

overlays/fix-qcom-modem/overlay.json

+      "cmd": "chmod 755 /persist/rmts"
+    },
+
+    // Create modem partition symlinks in /persist/rmts


Comment references /persist/rmts but should be /persist/rmtfs to match the rmtfs service requirements.

Suggested change

// Create modem partition symlinks in /persist/rmts

// Create modem partition symlinks in /persist/rmtfs

Copilot · 2025-12-04T18:58:23Z

overlays/fix-qcom-modem/create-modem-symlinks.sh

+#!/bin/bash
+set -euo pipefail
+
+# Create modem partition symlinks in /persist/rmts


Comment references /persist/rmts but should be /persist/rmtfs to match the rmtfs service requirements.

Suggested change

# Create modem partition symlinks in /persist/rmts

# Create modem partition symlinks in /persist/rmtfs

Copilot · 2025-12-04T18:58:24Z

overlays/fix-qcom-modem/create-modem-symlinks.sh

+# Create modem partition symlinks in /persist/rmts
+cd /persist/rmts


Directory path uses rmts but should be rmtfs to match the rmtfs service directory structure.

Suggested change

# Create modem partition symlinks in /persist/rmts

cd /persist/rmts

# Create modem partition symlinks in /persist/rmtfs

cd /persist/rmtfs

Copilot · 2025-12-04T18:58:24Z

overlays/fix-qcom-modem/overlay.json

+      "cmd": "grep -q '# Tachyon modem support' /etc/fstab || cat files/fstab-entries >> /etc/fstab",
+      "ignore-errors": true


The ignore-errors flag is set to true, which could mask genuine errors. If the fstab append fails for reasons other than the entry already existing, the error will be silently ignored. Consider removing this flag and relying on the grep check to prevent duplicate entries, or add more specific error handling.

Suggested change

"cmd": "grep -q '# Tachyon modem support' /etc/fstab || cat files/fstab-entries >> /etc/fstab",

"ignore-errors": true

"cmd": "grep -q '# Tachyon modem support' /etc/fstab || cat files/fstab-entries >> /etc/fstab"

Copilot · 2025-12-04T18:58:25Z

overlays/fix-qcom-modem/overlay.json

+      "type": "chroot-cmd",
+      "cmd": "grep -q '# Tachyon modem support' /etc/fstab || cat files/fstab-entries >> /etc/fstab",


The command uses cat files/fstab-entries but commands execute in the chroot environment. The files/fstab-entries path is relative and won't exist inside the chroot. This file needs to be copied into the chroot first, or the command should reference an absolute path that has been copied in earlier.

Consider copying the fstab-entries file into the chroot first (e.g., to /tmp/fstab-entries), then use that path in the cat command:

{ "type": "copy-into-chroot", "source": "files/fstab-entries", "destination": "/tmp/fstab-entries", "permissions": "644" }, { "type": "chroot-cmd", "cmd": "grep -q '# Tachyon modem support' /etc/fstab || cat /tmp/fstab-entries >> /etc/fstab", "ignore-errors": true }

Suggested change

"type": "chroot-cmd",

"cmd": "grep -q '# Tachyon modem support' /etc/fstab || cat files/fstab-entries >> /etc/fstab",

"type": "copy-into-chroot",

"source": "files/fstab-entries",

"destination": "/tmp/fstab-entries",

"permissions": "644"

},

{

"type": "chroot-cmd",

"cmd": "grep -q '# Tachyon modem support' /etc/fstab || cat /tmp/fstab-entries >> /etc/fstab",

Copilot · 2025-12-04T18:58:25Z

overlays/fix-qcom-modem/files/ModemManager-override.conf

+[Service]
+RestrictAddressFamilies=
+RestrictAddressFamilies=AF_NETLINK AF_UNIX AF_QIPCRTR AF_INET AF_INET6
+
+Environment=MM_PLUGIN_DEBUG=qcom-soc
+ExecStart=
+ExecStart=/usr/sbin/ModemManager --debug
+
+[Unit]
+# Ensure rmtfs is up before ModemManager starts
+After=rmtfs.service
+Requires=rmtfs.service
+
+[Service]
+# Add a delay to ensure the modem has initialized and QRTR is populated
+ExecStartPre=/bin/sleep 10


The [Service] section appears twice in this systemd override file (lines 1 and 14). While systemd will merge these sections, it's a best practice to consolidate all Service directives under a single [Service] section for clarity and maintainability. Consider restructuring as:

[Unit] After=rmtfs.service Requires=rmtfs.service [Service] RestrictAddressFamilies= RestrictAddressFamilies=AF_NETLINK AF_UNIX AF_QIPCRTR AF_INET AF_INET6 Environment=MM_PLUGIN_DEBUG=qcom-soc ExecStartPre=/bin/sleep 10 ExecStart= ExecStart=/usr/sbin/ModemManager --debug

Copilot · 2025-12-04T18:58:25Z

overlays/fix-qcom-modem/overlay.json

+    },
+    {
+      "type": "chroot-cmd",
+      "cmd": "mkdir -p /persist/rmts"


Typo in directory name: rmts should be rmtfs (Remote File System service). This is inconsistent with the service name rmtfs and could cause the service to fail since it expects data in /persist/rmtfs not /persist/rmts.

Copilot · 2025-12-04T18:58:25Z

overlays/fix-qcom-modem/files/rmtfs-override.conf

@@ -0,0 +1,3 @@
+[Service]
+ExecStart=
+ExecStart=/usr/bin/rmtfs -P -o /persist/rmts -s -v


The -o path parameter uses /persist/rmts but should be /persist/rmtfs to match the standard rmtfs directory structure.

Copilot · 2025-12-04T18:58:26Z

overlays/fix-qcom-modem/overlay.json

+    // Set up /persist directory structure and permissions
+    {
+      "type": "chroot-cmd",
+      "cmd": "chmod 755 /persist"
+    },
+    {
+      "type": "chroot-cmd",
+      "cmd": "mkdir -p /persist/rmts"
+    },
+    {
+      "type": "chroot-cmd",
+      "cmd": "chmod 755 /persist/rmts"
+    },


Setting permissions on /persist before it's mounted could be ineffective. The /persist directory is created at line 20, but according to the fstab entries, /dev/sdf8 should be mounted to /persist. The chmod operations at lines 33 and 41 will apply to the empty mount point, not the mounted filesystem. These permission changes should occur after the partitions are mounted, or they should be part of a post-mount initialization script.

Add in the modem overlay controls

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Copilot AI review requested due to automatic review settings December 4, 2025 18:53

Copilot started reviewing on behalf of mrlambchop December 4, 2025 18:53 View session

Copilot finished reviewing on behalf of mrlambchop December 4, 2025 18:55

Copilot AI reviewed Dec 4, 2025

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mrlambchop added 9 commits December 4, 2025 19:52

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	// Create modem partition symlinks in /persist/rmts
	// Create modem partition symlinks in /persist/rmtfs

	# Create modem partition symlinks in /persist/rmts
	# Create modem partition symlinks in /persist/rmtfs

		# Create modem partition symlinks in /persist/rmts
		cd /persist/rmts

		"cmd": "grep -q '# Tachyon modem support' /etc/fstab \|\| cat files/fstab-entries >> /etc/fstab",
		"ignore-errors": true

		"type": "chroot-cmd",
		"cmd": "grep -q '# Tachyon modem support' /etc/fstab \|\| cat files/fstab-entries >> /etc/fstab",

-      "type": "chroot-cmd",
-      "cmd": "grep -q '# Tachyon modem support' /etc/fstab || cat files/fstab-entries >> /etc/fstab",
+      "type": "copy-into-chroot",
+      "source": "files/fstab-entries",
+      "destination": "/tmp/fstab-entries",
+      "permissions": "644"
+    },
+    {
+      "type": "chroot-cmd",
+      "cmd": "grep -q '# Tachyon modem support' /etc/fstab || cat /tmp/fstab-entries >> /etc/fstab",

Add in the modem overlay controls #7

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mrlambchop commented Dec 4, 2025

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