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Re: [PATCH 3/5] zfs com.delphix:hole_birth feature support
From: |
Toomas Soome |
Subject: |
Re: [PATCH 3/5] zfs com.delphix:hole_birth feature support |
Date: |
Sun, 19 Apr 2015 17:40:16 +0300 |
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.
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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