Re: [PATCH]btrfs: avoid comparing with NULL pointer

[Liuwenyi]

ä 2010å01æ27æ 16:00, Yan, Zheng åé:
> 2010/1/27 Liuwenyi<qingshenlwy@xxxxxxxxx>:
>    
> > In this patch, I adjust the seqence of if-conditions.
> > It will assess the page->private situation.
> > First, we make sure the page->private is not null.
> > And then, we can do some with this page->private.
> >
> > ---
> > Signed-off-by: Liuwenyi<qingshenlwy@xxxxxxxxx>
> > Cc: Chris Mason<chris.mason@xxxxxxxxxx>
> > Cc: Yan Zheng<zheng.yan@xxxxxxxxxx>
> > Cc: Josef Bacik<jbacik@xxxxxxxxxx>
> > Cc: Jens Axboe<jens.axboe@xxxxxxxxxx>
> > Cc: linux-btrfs@xxxxxxxxxxxxxxx
> > Cc: linux-kernel@xxxxxxxxxxxxxxx
> >
> > ---
> > fs/btrfs/disk-io.c | 4 ++--
> > 1 files changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> > index 009e3bd..a300dca 100644
> > --- a/fs/btrfs/disk-io.c
> > +++ b/fs/btrfs/disk-io.c
> > @@ -1407,11 +1407,11 @@ static int bio_ready_for_csum(struct bio *bio)
> >
> > bio_for_each_segment(bvec, bio, i) {
> > page = bvec->bv_page;
> > - if (page->private == EXTENT_PAGE_PRIVATE) {
> > + if (!page->private) {
> > length += bvec->bv_len;
> > continue;
> > }
> > - if (!page->private) {
> > + if (page->private == EXTENT_PAGE_PRIVATE) {
> > length += bvec->bv_len;
> > continue;
> > }
> > --
> >      
> Why do you want to do this? The code is perfect safe even
> page->private is NULL. Furthermore, your patch is malformed.
>
> Yan, Zheng
>    
Yes, I agree with you, this code is safe.
But I think we should check whether the pointer is available first.
It is unnecessary judge the "(page->private == EXTENT_PAGE_PRIVATE)"
while page->private is null.


---
Best Regards,
Liuwenyi
2010-1-27

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