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

[Andrei Borzenkov]

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?

> 
> 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]) > \
> > 
> > 
> > _______________________________________________
> > Grub-devel mailing list
> > address@hidden
> > https://lists.gnu.org/mailman/listinfo/grub-devel
> 
> 
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