Re: [PATCH v2 2/2] btrfs: pass disk_bytenr directly for check_data_csum()

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

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On 2020/11/10 下午11:30, Josef Bacik wrote:
> On 11/9/20 9:09 PM, Qu Wenruo wrote:
>> Parameter @icsum for check_data_csum() is a little hard to understand.
>> So is the @phy_offset for btrfs_verify_data_csum().
>>
>> Both parameters are calculated values for csum lookup.
>>
>> Instead of some calculated value, just pass @disk_bytenr and let the
>> final and only user, check_data_csum(), to calculate whatever it needs.
>>
>> Signed-off-by: Qu Wenruo <wqu@suse.com>
>> ---
>>   fs/btrfs/extent_io.c | 14 ++++++++------
>>   fs/btrfs/inode.c     | 26 +++++++++++++++++---------
>>   2 files changed, 25 insertions(+), 15 deletions(-)
>>
>> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
>> index bd5a22bfee68..f8b5d3d4e5b0 100644
>> --- a/fs/btrfs/extent_io.c
>> +++ b/fs/btrfs/extent_io.c
>> @@ -2878,7 +2878,7 @@ static void end_bio_extent_readpage(struct bio
>> *bio)
>>       struct btrfs_io_bio *io_bio = btrfs_io_bio(bio);
>>       struct extent_io_tree *tree, *failure_tree;
>>       struct processed_extent processed = { 0 };
>> -    u64 offset = 0;
>> +    u64 disk_bytenr = (bio->bi_iter.bi_sector << 9);
> 
> This doesn't work, bi_sector can be remapped based on the underlying
> device, and thus can be different between submit and endio.  To
> illustrate this point, make 2 partitions on a single device, mkfs the
> second partition, and then run xfstests with this patch applied, all
> sorts of fun will happen.

Then it still doesn't matter.

The important thing is, we only use that "disk_bytenr" to calculate the
offset against the beginning of the bio.

Thus the result is the same.

Although the new naming would be a little confusing then, it's not
really disk_bytenr used by btrfs.

In that case, if we want (and I believe we want) real disk_bytenr,
btrfs_io_bio would be the correct location to add this member.

> 
> In fact we should probably add such a test to xfstests to catch anybody
> relying on bi_sector to stay the same.  Thanks,

Thankfully, not for this patch.

Thanks,
Qu

> 
> Josef


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