Re: Access content of file via inodes

[Martin Jambor <jamborm@gmail.com>]

Hi,

On 5/29/05, Anton Altaparmakov <aia21@cam.ac.uk> wrote:
> > I implemented it usng the same approach which ext2 uses to modify its
> > directories and believe that is the corect way (by calling aops
> > prepare and commit methods). The only thing that puzzles me is that
> 
> Yes that isw fine.  Just note that prepare/commit write need to run under
> i_sem protection.  But if you are already serializing access to the file
> some other way then you can ignore i_sem.

Do they? Documentation/filesystems/Locking only says they want their
page locked... but thanks for telling me, I will check that.

> > ext2 does not call flush_dcache_page that you suggested. Since it
> > seems to be an architecture specific function, I have no clue what so
> > ever whether I need to call it or not.
> 
> Well, as far as I understand it, this function causes changes to the page
> contents to become visible on all CPUs and from all processes and needs to
> be run before you unlock a page/mark it up to date otherwise someone who
> then locks it and/or reads it will possibly read old data from the page
> that is no longer correct. 

Some folks on irc sent me a link to an article that explains this
coherency stuff:
http://www.informit.com/articles/article.asp?p=29961&seqNum=6&rl=1
Basically, you need to call this only if the page might afterwards be
read from the userspace. Directories are not, so ext2 doesn't have to.

Thanks again,

Martin