Re: which dentry a page belongs to

[Jan Hudec <bulb@ucw.cz>]

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On Fri, Apr 23, 2004 at 18:01:30 +0100, Christoph Hellwig wrote:
> On Fri, Apr 23, 2004 at 12:52:54PM -0400, Shaya Potter wrote:
> > > in 2.4 writepage is always the result of data dirtied by mmap.  In 2.6 it's
> > > also for use for data dirtied by write.  Even in 2.4 there's no gurantee
> > > the mapping that dirtied the page still exists when the page is written out
> > > by the VM.
> > 
> > so the mapping off the page struct will be null?
> 
> No. but i_mmap and i_mmap_shared might be empty.
> 
> > so is that a yes to my understanding of "multiple dentries" i.e. a
> > single inode linked into multiple places in the fs.
> 
> Yes.
> 
> > > > > It's also possible to find no dentries at all.
> > > > 
> > > > even if in my fs's writepage() function?
> > > 
> > > Yes.
> > 
> > so the vm_file part of vm_area_struct will be null?
> 
> You won't find a vm_area_struct at all in that case.
> 
> > > You can't do that.
> > 
> > Yes, I know it's evil to do and would never be accepted into the kernel
> > proper, the question I'm trying to figure out if it it's possible (with
> > a stackable fs) to version files on write.  
> 
> It's not evil is's fucking impossible for gods sake.
> 
> you can be in writepage with page->mapping->i_mmap{,shared} beeing empty.
> No way in hell you'll ever get to a dentry.

page->mapping->host->i_dentries and first item there? Of course, inode
can survive it's last dentry. But you can make sure it won't survive
dirty!

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						 Jan 'Bulb' Hudec <bulb@ucw.cz>

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