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Re: JFFS2 and XIP





On Wed, 22 Aug 2001, A. Craig West wrote:

> As far as I know, jffs2 doesn't support XIP code. Is there any hope of adding
> support for it? cramfs supports it with a method of marking individual files
> as being XIP so that they are not compressed. I believe they use the sticky
> bit to mark the file...
> For the types of applications that jffs2 is designed for, XIP can be at least
> as important as file compression, so it would be good if we supported both...

JFFS2 has been designed to be able to _write_ to flash.  The problem with
most if not all flash chips is that when you put them into write mode the
content of the flash data is unavailable.  This is even worse when you need
to erase flash sectors since that operation is extremely long (relatively
speaking of course).  This makes XIP and erasing/writing to flash mutually
exclusive since you must prevent any fetch from flash pages while any
erasing/writing is in process which becomes extremely complex and silly from
an implementation point of view.

Therefore if you don't need to write to flash then stick with cramfs.
Otherwise don't forget that Linux only loads executable pages on demand and
drop old/unused pages when something needs memory (unless you don't have a
MMU).


Nicolas


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