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Editing File: /snap/core20/2686/usr/lib/udev/rules.d/78-sound-card.rules

# do not edit this file, it will be overwritten on update

SUBSYSTEM!="sound", GOTO="sound_end"

ACTION=="add|change", KERNEL=="controlC*", ATTR{../uevent}="change"
ACTION!="change", GOTO="sound_end"

# Ok, we probably need a little explanation here for what the two lines above
# are good for.
#
# The story goes like this: when ALSA registers a new sound card it emits a
# series of 'add' events to userspace, for the main card device and for all the
# child device nodes that belong to it. udev relays those to applications,
# however only maintains the order between father and child, but not between
# the siblings. The control device node creation can be used as synchronization
# point. All other devices that belong to a card are created in the kernel
# before it. However unfortunately due to the fact that siblings are forwarded
# out of order by udev this fact is lost to applications.
#
# OTOH before an application can open a device it needs to make sure that all
# its device nodes are completely created and set up.
#
# As a workaround for this issue we have added the udev rule above which will
# generate a 'change' event on the main card device from the 'add' event of the
# card's control device. Due to the ordering semantics of udev this event will
# only be relayed after all child devices have finished processing properly.
# When an application needs to listen for appearing devices it can hence look
# for 'change' events only, and ignore the actual 'add' events.
#
# When the application is initialized at the same time as a device is plugged
# in it may need to figure out if the 'change' event has already been triggered
# or not for a card. To find that out we store the flag environment variable
# SOUND_INITIALIZED on the device which simply tells us if the card 'change'
# event has already been processed.

KERNEL!="card*", GOTO="sound_end"

ENV{SOUND_INITIALIZED}="1"

IMPORT{builtin}="hwdb"
SUBSYSTEMS=="usb", IMPORT{builtin}="usb_id"
SUBSYSTEMS=="usb", GOTO="skip_pci"

SUBSYSTEMS=="firewire", ATTRS{guid}=="?*", \
  ENV{ID_BUS}="firewire", ENV{ID_SERIAL}="$attr{guid}", ENV{ID_SERIAL_SHORT}="$attr{guid}", \
  ENV{ID_VENDOR_ID}="$attr{vendor}", ENV{ID_MODEL_ID}="$attr{model}", \
  ENV{ID_VENDOR}="$attr{vendor_name}", ENV{ID_MODEL}="$attr{model_name}"
SUBSYSTEMS=="firewire", GOTO="skip_pci"

SUBSYSTEMS=="pci", ENV{ID_BUS}="pci", ENV{ID_VENDOR_ID}="$attr{vendor}", ENV{ID_MODEL_ID}="$attr{device}"
SUBSYSTEMS=="pci", GOTO="skip_pci"

# If we reach here, the device nor any of its parents are USB/PCI/firewire bus devices.
# If we now find a parent that is a platform device, assume that we're working with
# an internal sound card.
SUBSYSTEMS=="platform", ENV{SOUND_FORM_FACTOR}="internal", GOTO="sound_end"

LABEL="skip_pci"

# Define ID_ID if ID_BUS and ID_SERIAL are set. This will work for both
# USB and firewire.
ENV{ID_SERIAL}=="?*", ENV{ID_USB_INTERFACE_NUM}=="?*", ENV{ID_ID}="$env{ID_BUS}-$env{ID_SERIAL}-$env{ID_USB_INTERFACE_NUM}"
ENV{ID_SERIAL}=="?*", ENV{ID_USB_INTERFACE_NUM}=="", ENV{ID_ID}="$env{ID_BUS}-$env{ID_SERIAL}"

IMPORT{builtin}="path_id"

# The values used here for $SOUND_FORM_FACTOR and $SOUND_CLASS should be kept
# in sync with those defined for PulseAudio's src/pulse/proplist.h
# PA_PROP_DEVICE_FORM_FACTOR, PA_PROP_DEVICE_CLASS properties.

# If the first PCM device of this card has the pcm class 'modem', then the card is a modem
ATTR{pcmC%nD0p/pcm_class}=="modem", ENV{SOUND_CLASS}="modem", GOTO="sound_end"

# Identify cards on the internal PCI bus as internal
SUBSYSTEMS=="pci", DEVPATH=="*/0000:00:??.?/sound/*", ENV{SOUND_FORM_FACTOR}="internal", GOTO="sound_end"

# Devices that also support Image/Video interfaces are most likely webcams
SUBSYSTEMS=="usb", ENV{ID_USB_INTERFACES}=="*:0e????:*", ENV{SOUND_FORM_FACTOR}="webcam", GOTO="sound_end"

# Matching on the model strings is a bit ugly, I admit
ENV{ID_MODEL}=="*[Ss]peaker*", ENV{SOUND_FORM_FACTOR}="speaker", GOTO="sound_end"
ENV{ID_MODEL_FROM_DATABASE}=="*[Ss]peaker*", ENV{SOUND_FORM_FACTOR}="speaker", GOTO="sound_end"

ENV{ID_MODEL}=="*[Hh]eadphone*", ENV{SOUND_FORM_FACTOR}="headphone", GOTO="sound_end"
ENV{ID_MODEL_FROM_DATABASE}=="*[Hh]eadphone*", ENV{SOUND_FORM_FACTOR}="headphone", GOTO="sound_end"

ENV{ID_MODEL}=="*[Hh]eadset*", ENV{SOUND_FORM_FACTOR}="headset", GOTO="sound_end"
ENV{ID_MODEL_FROM_DATABASE}=="*[Hh]eadset*", ENV{SOUND_FORM_FACTOR}="headset", GOTO="sound_end"

ENV{ID_MODEL}=="*[Hh]andset*", ENV{SOUND_FORM_FACTOR}="handset", GOTO="sound_end"
ENV{ID_MODEL_FROM_DATABASE}=="*[Hh]andset*", ENV{SOUND_FORM_FACTOR}="handset", GOTO="sound_end"

ENV{ID_MODEL}=="*[Mm]icrophone*", ENV{SOUND_FORM_FACTOR}="microphone", GOTO="sound_end"
ENV{ID_MODEL_FROM_DATABASE}=="*[Mm]icrophone*", ENV{SOUND_FORM_FACTOR}="microphone", GOTO="sound_end"

LABEL="sound_end"

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