(tl;dr: is there a nicer/better way to link a UDisks device with a .mpi file than using NativePath and walking up the parent tree of the disk using UDev? If not, should there be?)
Suppose we have the following situation: someone plugs in a portable USB media
player that presents itself as a storage device. A Sansa Clip+ in MSC mode,
say (since that's actually what I have).
In the days of HAL, this would cause many devices to appear in HAL's device
tree. The topmost device would be recognised as a media player, and one of
the subdevices would be registered as a block device, say sdc. The media
player properties set by 10-usb-music-player.fdi would be propagated down to
this device, which would have both the storage_volume capability and the
portable_audio_player capability. The specific properties, such as what media
formats the device supported, would all be available from this point.
No we no longer have HAL, and plugging in such a device will make a device
(sdc, say) appear in UDisks' device tree. However, UDisks knows nothing about
media players.
Instead, there is media-player-info. On Linux, it is possible to listen to
UDev devices and find a device with the ENV{ID_MEDIA_PLAYER} property set to
some value that allows you to find a .mpi file with the relevant info in. Fine.
Typically, media applications will want these things to be linked - they want
to know both the block device they should be accessing (or, rather, the folder
that UDisks mounted it at) and what formats they can place on the device. One
way of doing this is to get the NativePath and walk up the tree in UDev
looking for ENV{ID_MEDIA_PLAYER}.
My question is: is there a better way? UDisks is ostensibly portable to non-
Linux systems. As is media-player-info. But UDev isn't. So applications
have to take two bits of platform-agnostic data and link them together with
platform-specific glue. This doesn't seem very nice.
Sorry for the long-winded email.
Alex
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