Well I was thinking more like this...

[stream of consciousness mode ON]

Instead of the user apps asking for specific blocks, there could be a lightweight API which takes as its inputs an application identifier and some kind of offset.

The app identifier would ensure that the lyrics scroller wouldn't ask for the same blocks that the OBD-II logger would ask for. Then the numeric index could be an offset, or maybe a block number within the range assigned to each application.

So let's say I've got an Empeg with my (now fictitious) lyrics scroller time tagger, the also fictitious OBD-II diagnostic logger, and the shopping list/directions thingie.

Somehow this API would read in (possibly from config.ini) a configuration for the "virtual disk" like this:
LYRICS, 16
OBD2, 64
SHOPLIST, 16

So it would give the lyrics scroller the first 16k, the OBD2 logger the next 64k, and the shopping list thing the next 16k. A call from the OBD2 logger would look like this:

empeg_storage_write("OBD2", 4, &buf)

When the storage API gets this call, it writes to the OBD2 "base" of 16k plus the 4k offset. Offsets could, of course, be in bytes or whatever for finer grain.

Obviously this is a bit more work than just an offset. I think If the kernel code was there for writing to a specific block, I MIGHT be able to string together the user code to call it properly. If not, I'm sure some other smart person could.

Does this API seem feasible? I think it would be a good way for users to have multiple apps which all would like to write data to the disk.