Re: [PATCH v4 17/18] btrfs: dedup: add a property handler for online dedup

[Qu Wenruo <quwenruo@cn.fujitsu.com>]

Filipe Manana wrote on 2016/01/14 09:56 +0000:
> On Thu, Jan 14, 2016 at 5:57 AM, Qu Wenruo <quwenruo@cn.fujitsu.com> wrote:
>> From: Wang Xiaoguang <wangxg.fnst@cn.fujitsu.com>
>>
>> We use btrfs extended attribute "btrfs.dedup" to record per-file online
>> dedup status, so add a dedup property handler.
>>
>> Signed-off-by: Wang Xiaoguang <wangxg.fnst@cn.fujitsu.com>
>> ---
>>   fs/btrfs/props.c | 40 ++++++++++++++++++++++++++++++++++++++++
>>   1 file changed, 40 insertions(+)
>>
>> diff --git a/fs/btrfs/props.c b/fs/btrfs/props.c
>> index f9e6023..ae8b76d 100644
>> --- a/fs/btrfs/props.c
>> +++ b/fs/btrfs/props.c
>> @@ -41,6 +41,10 @@ static int prop_compression_apply(struct inode *inode,
>>                                    size_t len);
>>   static const char *prop_compression_extract(struct inode *inode);
>>
>> +static int prop_dedup_validate(const char *value, size_t len);
>> +static int prop_dedup_apply(struct inode *inode, const char *value, size_t len);
>> +static const char *prop_dedup_extract(struct inode *inode);
>> +
>>   static struct prop_handler prop_handlers[] = {
>>          {
>>                  .xattr_name = XATTR_BTRFS_PREFIX "compression",
>> @@ -49,6 +53,13 @@ static struct prop_handler prop_handlers[] = {
>>                  .extract = prop_compression_extract,
>>                  .inheritable = 1
>>          },
>> +       {
>> +               .xattr_name = XATTR_BTRFS_PREFIX "dedup",
>> +               .validate = prop_dedup_validate,
>> +               .apply = prop_dedup_apply,
>> +               .extract = prop_dedup_extract,
>> +               .inheritable = 1
>> +       },
>>   };
>>
>>   void __init btrfs_props_init(void)
>> @@ -425,4 +436,33 @@ static const char *prop_compression_extract(struct inode *inode)
>>          return NULL;
>>   }
>>
>> +static int prop_dedup_validate(const char *value, size_t len)
>> +{
>> +       if (!strncmp("disable", value, len))
>> +               return 0;
>> +
>> +       return -EINVAL;
>> +}
>> +
>> +static int prop_dedup_apply(struct inode *inode, const char *value, size_t len)
>> +{
>> +       if (len == 0) {
>> +               BTRFS_I(inode)->flags &= ~BTRFS_INODE_NODEDUP;
>> +               return 0;
>> +       }
>> +
>> +       if (!strncmp("disable", value, len)) {
>> +               BTRFS_I(inode)->flags |= BTRFS_INODE_NODEDUP;
>> +               return 0;
>> +       }
>> +
>> +       return -EINVAL;
>> +}
>> +
>> +static const char *prop_dedup_extract(struct inode *inode)
>> +{
>> +       if (BTRFS_I(inode)->flags | BTRFS_INODE_NODEDUP)
>> +               return "disable";
>
> | -> &
>
> How about writing test cases (for xfstests)? Not only for the property
> but for the whole dedup feature, it would avoid such simple
> mistakes...

Yes, it's already in our schedule and we have some internal simple test 
case.

But the problem is,
Some behavior/format is not completely determined yet
Especially for on-disk format (ondisk backend only), and ioctl interface.

So I'm a little concerned about submit them too early before we made 
final decision on the ioctl interface.

> Take a look at the good example of xfs development. For example when
> all the recent patches for their reflink implementation was posted
> (and before getting merged), a comprehensive set of test cases for
> xfstests was also posted...

Yes, test driven development is very nice, but there is also problem, 
especially for btrfs, like btrfs/047 which needs btrfs send 
--stream-version support.

But unfortunately, there is not --stream-version support in upsteam 
btrfs-progs and the test case never get executed on upsteam btrfs-progs.

Personally speaking, xfs development can only happen in that way because 
xfstest maintainer is also the maintainer of xfs.
As Dave knows every aspect of xfs and can determine which feature will 
be merged.
But that's not true for btrfs, so he can merge wrong patch and cause 
inconsistent with what btrfs really supports between test cases.

Thanks,
Qu

>
>>
>> +       return NULL;
>> +}
>> --
>> 2.7.0
>>
>>
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>
>
>