SD card does not auto mount like a USB stick does

jnorth commented 1 year ago

I don't believe this is an issue with myMPDos specifically, but wanted to raise here in case it was a configuration value set by the image. Feel free to close if this is out of this project's scope.

When I plug a USB stick into the Raspberry Pi, it's files are automatically mounted and accessible.

When I plug in a USB card reader, its device is detected, but when I insert an SD card into that it is not mounted or accessible.

Lastly, if I plug in the SD card before inserting the USB card reader, it is automatically mounted and accessible. Strange!

[RaspberryPi] -- Micro USB -- [USB Card Reader] -- SD Slot -- [SD Card]

I've tried with a couple different USB card readers, and a couple different SD cards, and non seem to support hot swapping the SD card. I've posted a question to the unix/linux Stack Exchange, and hopefully someone can point me in the right direction. More details in that post if this seems like something that could be configured through this distribution:

https://unix.stackexchange.com/questions/730184/with-a-usb-sd-card-reader-the-sd-card-only-shows-up-if-it-is-inserted-before-th

jcorporation commented 1 year ago

myMPDos uses a custom script for automounting: /usr/bin/automount.sh. This script is triggered by mdev. Config file is /etc/mdev.conf. You should look, if mdev triggers an event on sd-card insertion.

jnorth commented 1 year ago

Thanks, that helps point me in the right direction.

mdev is indeed not triggering events for the sd-card insertion/removal, so the issue is happening in mdev or somewhere further upstream. The mdev config looks good, as does the auto mount.sh script 👍.

I'll update here if I find a solution in case it helps anyone else, but I'll close the ticket since it's not at the myMPDos level.

jnorth commented 1 year ago

Just wanted to share an update here in case it helped anyone else.

There very well could be a better solution which enables mdev to trigger events for the SD card being inserted or removed. It seems like it could be a missing configuration or module somewhere in the system, but nothing I did was able to get an event to fire that I could use.

Instead, I installed udev using the setup-devd command, and modified the udev rules to replicate some of what myMPDos is doing with the mdev.conf and automount.sh scripts. It works!

NOTE: This still feels pretty hacky. When inserting the SD card, I get an add event and mount the device. Removing the card however does not fire a remove event if the music files are in use. Instead, I also listen for change events, and unmount on those if I detect the change event firing for a previously mounted device. Good enough for me for now, but I think the right approach would be to tell MPD to remove the files on change and hopefully that would let the remove event trigger normally.

Anyway, here is what I've done:

Replace mdev with udev

setup-devd

Enter udev and choose y to repopulate hardware.

Add udev rules file to listen for sd devices

Create a file /etc/udev/rules.d/10-sd.rules:

KERNEL=="sd[a-z]*", RUN+="/usr/bin/automount.sh"

Modify the automount.sh script

Replace /usr/bin/automount.sh with:

#!/bin/sh
#
# SPDX-License-Identifier: GPL-3.0-or-later
# myMPDos (c) 2020-2022 Juergen Mang <mail@jcgames.de>
# https://github.com/jcorporation/myMPDos

MDEV="$(basename $DEVNAME)"
MOUNTDIR="/mnt/$MDEV"

if [ "$ACTION" = "add" ]
then
  # Mount device
  mkdir "$MOUNTDIR"
  mount -oro,noatime "$DEVNAME" "$MOUNTDIR"

  # Update music database
  [ -f /run/mpd/pid ] && mpc update

elif [ "$ACTION" = "change" ]
then
  # Scan each mount point
  # The change action happens at the root (sda vs sda1), so we loop through and unmount any partitions using that root
  for MOUNT in /mnt/*/
  do
    MOUNTNAME=$(basename $MOUNT)

    if [ "$(echo $MOUNTNAME | sed 's/[0-9]//g')" = "$MDEV" ]
    then
      # Unmount device
      umount "$MOUNT"
      rmdir "$MOUNT"

      # Update music database
      [ -f /run/mpd/pid ] && mpc update
    fi
  done

elif [ "$ACTION" = "remove" ]
then
  # Unmount device
  umount "$MOUNTDIR"
  rmdir "$MOUNTDIR"

  # Update music database
  [ -f /run/mpd/pid ] && mpc update
fi

You may need to reload the udev rules to get it to follow the new 10-sd.rules file.

udevadm control --reload-rules && udevadm trigger

jcorporation commented 1 year ago

Thanks for sharing this!

mdev has a change event. Had you tried this event?

jcorporation / myMPDos