.truncate function in filesystems

All,

I'm rather at a loss to understand what .truncate is supposed to do when it _extends_ a file (2.5.68+ kernel). Looking through the examples in the tree, I don't see where they deal with that case. Could someone give me a clue as to how .truncate is supposed to...tell the kernel what blocks it is to use when it goes to read from the extended portion of the file?

So far, I have googled, grep'ed, looked at lwn.net, started in on linux.bkbits.net, emailed linux-fsdevel and kernel-newbies... and I'm still not getting anywhere. Even a basic explanation of how filesystems
deal/interact with buffer heads and inodes would probably help at this
point.

Any clues or pointers or _anything_ would be very much appreciated. :/

Eli
--------------------. "If it ain't broke now,
Eli Carter \ it will be soon." -- crypto-gram
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