Re: File and device pages and buffers

[Martin Jambor <jamborm@gmail.com>]

Can I try to bring your attention once more to the following issue:

On 4/18/05, Martin Jambor <jamborm@gmail.com> wrote:
> There is one thing about cache pages and buffers that puzzles me and
> that I have not found in any documenatation and that is not quite
> obvious from the source.
> 
> What is the relationship between:
> a) pages and their buffers associated with the device (typically
> bh->bdev->bd_inode and its mapping) and
> 
> b) pages and their buffers associated with files on that device.
> 
> Can anyone tell me  what the relationship exactly is and what one has
> to be aware of when manipulating either of these?

My conclusion from reading the source is that after mapping a file
buffer (buffer belonging to a page that is a part of a file on a
device) to a particular block on a device, one should call
unmap_underlying_metadata to make sure any writing using a device
buffer will not overwrite the file. And that one must not use device
buffers to write to places which have been mapped to files.

Is that correct?

TIA

Martin