Re: [PATCH] Add compability for kernels >=2.6.27-rc1

[Chris Mason <chris.mason@oracle.com>]

On Wed, 2008-07-30 at 21:56 +0200, Jens Axboe wrote:
> On Wed, Jul 30 2008, Sven Wegener wrote:
> > Add a couple of #if's to follow API changes.
> > 
> > Signed-off-by: Sven Wegener <sven.wegener@stealer.net>
> > ---
> >  extent_io.c |   16 ++++++++++++++++
> >  file.c      |    4 ++++
> >  inode.c     |   12 ++++++++++--
> >  3 files changed, 30 insertions(+), 2 deletions(-)
> > 
> > Having passed the rc1 mark the API changes should be finished.
> > 
> > Other #if in the source use >version instead of >=version+1, so I use them 
> > too.
> > 
> > Patch is against the current unstable repository, but can applied with a 
> > slight modification (extent_io.c) to the stable repository too.
> > 
> > diff -r 59ec68fb1540 extent_io.c
> > --- a/extent_io.c	Wed Jul 30 10:29:12 2008 -0400
> > +++ b/extent_io.c	Wed Jul 30 19:00:28 2008 +0000
> > @@ -2649,9 +2649,17 @@
> >  	mapping = eb->first_page->mapping;
> >  	if (!mapping)
> >  		return NULL;
> > +#if LINUX_VERSION_CODE > KERNEL_VERSION(2,6,26)
> > +	spin_lock_irq(&mapping->tree_lock);
> > +#else
> >  	read_lock_irq(&mapping->tree_lock);
> > +#endif
> >  	p = radix_tree_lookup(&mapping->page_tree, i);
> > +#if LINUX_VERSION_CODE > KERNEL_VERSION(2,6,26)
> > +	spin_unlock_irq(&mapping->tree_lock);
> > +#else
> >  	read_unlock_irq(&mapping->tree_lock);
> > +#endif
> >  	return p;
> >  }
> 
> For btrfs's usage, it should be safe with a simple rcu_read_lock(), if
> the return is referenced safely.
> 

This btrfs code is basically a find_get_page without the get.  It should
only be called when I know I already have a reference on the page.

-chris