[PATCH]btrfs: avoid comparing with NULL pointer

[PATCH]btrfs: avoid comparing with NULL pointer

[Liuwenyi]

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@gmail.com>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Yan Zheng <zheng.yan@oracle.com>
Cc: Josef Bacik <jbacik@redhat.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: linux-btrfs@vger.kernel.org
Cc: linux-kernel@vger.kernel.org

---
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;
}
-- 
1.6.6


---
Best Regards,
Liuwenyi
2010-01-277

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

[Yan, Zheng]

2010/1/27 Liuwenyi <qingshenlwy@gmail.com>:
> 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@gmail.com>
> Cc: Chris Mason <chris.mason@oracle.com>
> Cc: Yan Zheng <zheng.yan@oracle.com>
> Cc: Josef Bacik <jbacik@redhat.com>
> Cc: Jens Axboe <jens.axboe@oracle.com>
> Cc: linux-btrfs@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
>
> ---
> 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

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

[Liuwenyi]

于 2010年01月27日 16:00, Yan, Zheng 写道:
> 2010/1/27 Liuwenyi<qingshenlwy@gmail.com>:
>    
>> 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@gmail.com>
>> Cc: Chris Mason<chris.mason@oracle.com>
>> Cc: Yan Zheng<zheng.yan@oracle.com>
>> Cc: Josef Bacik<jbacik@redhat.com>
>> Cc: Jens Axboe<jens.axboe@oracle.com>
>> Cc: linux-btrfs@vger.kernel.org
>> Cc: linux-kernel@vger.kernel.org
>>
>> ---
>> 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