[PATCH v2 BlueZ 0/1] Add cover art support

[Jan-Michael <jan.brummer@tabos.org>]

BlueZ wasn't able to display cover art in car's headunits due to missing
cover art support. Add missing pieces to allow sending cover arts:

 - Add AVRCP BIP Cover Art Responder
 - Advertise Cover Art Support
 - Update bluetooth service to have at least read only access to home directories (where cover images are located)

v2:
Dropped the patch that relaxed the sandbox of the systemd unit.
bluetoothd no longer touches the filesystem at all: instead of
reading the file mpris:artUrl points to, it asks the player for the
image data over D-Bus, and mpris-proxy answers that call
for the players it registers (patch 5). ProtectHome= and the
capability bounding set stay exactly as they are.

Tested on a Fairphone 5 and OnePlus 6T with a VW head unit.

Jan-Michael Brummer (1):
  Add cover art support

 Makefile.plugins           |   4 +-
 doc/org.bluez.Media.rst    |  21 ++
 profiles/audio/avrcp-bip.c | 608 +++++++++++++++++++++++++++++++++++++
 profiles/audio/avrcp-bip.h |  46 +++
 profiles/audio/avrcp.c     |  92 +++++-
 profiles/audio/media.c     | 194 ++++++++++++
 src/bluetooth.conf         |   1 +
 tools/mpris-proxy.c        |  81 +++++
 8 files changed, 1041 insertions(+), 6 deletions(-)
 create mode 100644 profiles/audio/avrcp-bip.c
 create mode 100644 profiles/audio/avrcp-bip.h

-- 
2.55.0