Re: [PATCH 3/5] zfs com.delphix:hole_birth feature support

[Vladimir 'φ-coder/phcoder' Serbinenko]

Thank you Toomas for patch and Andrey for reviews.
On 03.05.2015 17:15, Andrei Borzenkov wrote:
> В Sun, 19 Apr 2015 17:57:04 +0300
> Toomas Soome <address@hidden> пишет:
> 
>>
>>> On 19.04.2015, at 17:51, Andrei Borzenkov <address@hidden> wrote:
>>>
>>> В Sun, 19 Apr 2015 17:40:16 +0300
>>> Toomas Soome <address@hidden> пишет:
>>>
>>>>
>>>> the features in openzfs have different effects, some affect only writes 
>>>> and are therefore read only compatible - such feature does not need any 
>>>> changes for reads, this feature is not read only compatible and therefore, 
>>>> once this feature is enabled, reader code must be changed accordingly.
>>>>
>>>> so, what they did with hole_birth was they started to insert block birth 
>>>> timestamps for blocks being released to make it possible to track such 
>>>> blocks while doing zfs send (when block has birth time, you know its place 
>>>> on timeline of snapshots). as old reader code was relying on blk_birth == 
>>>> 0 to detect an hole, after hole_birth is enabled, hole blk_birth is not 0 
>>>> any more, so the solution is to check if DVA pointers are zero instead. 
>>>> and thats exactly what its about.  
>>>
>>> And if hole_birth is *not* enabled on a filesystem we are reading?
>>> Should not old code be used in this case?
>>
>>
>> not really, as for holes, DVA pointers are  zero anyhow. I guess the 
>> original implementation used blk_birth to save extra compare - so the new 
>> read code is compatible with old data.
> 
> Committed with explanatory text for non-insiders.
> 
>>
>>
>>>
>>>>
>>>> reference:
>>>> https://github.com/illumos/illumos-gate/commit/43466aae47bfcd2ad9bf501faec8e75c08095e4f
>>>>  
>>>>
>>>>
>>>>
>>>>> On 19.04.2015, at 17:11, Andrei Borzenkov <address@hidden> wrote:
>>>>>
>>>>> В Thu, 16 Apr 2015 08:22:08 +0300
>>>>> Toomas Soome <address@hidden> пишет:
>>>>>
>>>>> This really needs better explanation. Otherwise this looks like either
>>>>> old code was broken to start with and it is a bug fix or new code needs
>>>>> some conditionals on new feature.
>>>>>
>>>>>>
>>>>>> ---
>>>>>> grub-core/fs/zfs/zfs.c |    6 ++++--
>>>>>> include/grub/zfs/spa.h |    4 +++-
>>>>>> 2 files changed, 7 insertions(+), 3 deletions(-)
>>>>>>
>>>>>> diff --git a/grub-core/fs/zfs/zfs.c b/grub-core/fs/zfs/zfs.c
>>>>>> index 2689986..a731c3d 100644
>>>>>> --- a/grub-core/fs/zfs/zfs.c
>>>>>> +++ b/grub-core/fs/zfs/zfs.c
>>>>>> @@ -280,7 +280,9 @@ grub_crypto_cipher_handle_t (*grub_zfs_load_key) 
>>>>>> (const struct grub_zfs_key *key
>>>>>> */
>>>>>> #define MAX_SUPPORTED_FEATURE_STRLEN 50
>>>>>> static const char *spa_feature_names[] = {
>>>>>> -  "org.illumos:lz4_compress",NULL
>>>>>> +  "org.illumos:lz4_compress",
>>>>>> +  "com.delphix:hole_birth",
>>>>>> +  NULL
>>>>>> };
>>>>>>
>>>>>> static int
>>>>>> @@ -1751,7 +1753,7 @@ zio_read_gang (blkptr_t * bp, grub_zfs_endian_t 
>>>>>> endian, dva_t * dva, void *buf,
>>>>>>
>>>>>>  for (i = 0; i < SPA_GBH_NBLKPTRS; i++)
>>>>>>    {
>>>>>> -      if (zio_gb->zg_blkptr[i].blk_birth == 0)
>>>>>> +      if (BP_IS_HOLE(&zio_gb->zg_blkptr[i]))
>>>>>>  continue;
>>>>>>
>>>>>>      err = zio_read_data (&zio_gb->zg_blkptr[i], endian, buf, data);
>>>>>> diff --git a/include/grub/zfs/spa.h b/include/grub/zfs/spa.h
>>>>>> index 7edb8ab..df43b6b 100644
>>>>>> --- a/include/grub/zfs/spa.h
>>>>>> +++ b/include/grub/zfs/spa.h
>>>>>> @@ -279,7 +279,9 @@ typedef struct blkptr {
>>>>>>
>>>>>> #define  BP_IDENTITY(bp)         (&(bp)->blk_dva[0])
>>>>>> #define  BP_IS_GANG(bp)          DVA_GET_GANG(BP_IDENTITY(bp))
>>>>>> -#define BP_IS_HOLE(bp)          ((bp)->blk_birth == 0)
>>>>>> +#define DVA_IS_EMPTY(dva)       ((dva)->dva_word[0] == 0ULL && \
>>>>>> +                                (dva)->dva_word[1] == 0ULL)
>>>>>> +#define BP_IS_HOLE(bp)          DVA_IS_EMPTY(BP_IDENTITY(bp))
>>>>>>
>>>>>> /* BP_IS_RAIDZ(bp) assumes no block compression */
>>>>>> #define  BP_IS_RAIDZ(bp)         (DVA_GET_ASIZE(&(bp)->blk_dva[0]) > \
>>>>>
>>>>>
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>>>>
>>>>
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>>
> 
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