On Mon, Dec 16, 2013 at 10:17:18AM -0600, Chandra Seetharaman wrote:
> On Mon, 2013-12-16 at 14:32 +0200, saeed bishara wrote:
> > On Thu, Dec 12, 2013 at 1:38 AM, Chandra Seetharaman
> > <sekharan@xxxxxxxxxx> wrote:
> > > In order to handle multiple extent buffers per page, first we
> > > need to create a way to handle all the extent buffers that
> > > are attached to a page.
> > >
> > > This patch creates a new data structure eb_head, and moves
> > > fields that are common to all extent buffers in a page from
> > > extent buffer to eb_head.
> > >
> > > This also adds changes that are needed to handle multiple
> > > extent buffers per page case.
> > >
> > > Signed-off-by: Chandra Seetharaman <sekharan@xxxxxxxxxx>
> > > ---
>
> <snip>
>
> > > diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> > > index 54ab861..02de448 100644
> > > --- a/fs/btrfs/ctree.h
> > > +++ b/fs/btrfs/ctree.h
> > > @@ -2106,14 +2106,16 @@ static inline void btrfs_set_token_##name(struct extent_buffer *eb, \
> > > #define BTRFS_SETGET_HEADER_FUNCS(name, type, member, bits) \
> > > static inline u##bits btrfs_##name(struct extent_buffer *eb) \
> > > { \
> > > - type *p = page_address(eb->pages[0]); \
> > > + type *p = page_address(eb_head(eb)->pages[0]) + \
> > > + (eb->start & (PAGE_CACHE_SIZE -1)); \
> > you can use PAGE_CACHE_MASK instead of PAGE_CACHE_SIZE - 1
>
> PAGE_CACHE_MASK get the page part of the value, not the offset in the
> page, i.e it is defined as
>
> #define PAGE_MASK (~(PAGE_SIZE-1))
Use ~PAGE_CACHE_MASK to get the offset. It's common, though not obvious
at first.
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