>What I meant by
>> via blocks is to gain knowledge of the physical blocks used by the 
inodes
>> and retrieve the content from it directly, by accessing b_data.
>
>The problem with that approach is that some filesystems may store part
>of the file outside of a complete block.

There's an even more basic problem with this approach:  The question is 
specifically about the filesystem-type-independent layer above the VFS 
interface.  At this layer, you don't even know that there is a block 
device involved.  And if you do, you don't know that the filesystem driver 
uses the buffer cache to access it.  And if you do know that it uses the 
buffer cache, you don't know that the file data you're looking for is 
presently in the buffer cache, or how to get it there if it isn't.

If you believe in the layering at all, the only interface you can consider 
at this layer for getting at file data is VFS ->read.

--
Bryan Henderson                               San Jose California
IBM Almaden Research Center                   Filesystems
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