[PATCH v3 0/6] block-status cache for data regions

[Hanna Reitz <hreitz@redhat.com>]

Hi,

See the cover letter from v1 for the general idea:
https://lists.nongnu.org/archive/html/qemu-block/2021-06/msg00843.html

Cover letter from v2, introducing RCU locking:
https://lists.nongnu.org/archive/html/qemu-block/2021-06/msg01060.html


v3:
- Patch 2:
  - Add rcu_head object to BdrvBlockStatusCache, so we can use
    g_free_rcu() to free it instead of synchronize_rcu()+g_free()
  - Use qatomic_rcu_read() every time we read bs->block_status_cache
    (except in bdrv_close(), where no concurrency is possible)
  - Use RCU_READ_LOCK_GUARD() instead of WITH_RCU_READ_LOCK_GUARD() in
    functions where we lock the whole scope anyway
  - Same for QEMU_LOCK_GUARD() instead of WITH_QEMU_LOCK_GUARD() in
    bdrv_bsc_fill()
  - Drop from_cache variable in bdrv_co_block_status()
    (was an artifact from v1, which had a different control flow and
    needed this variable)
  - Assert that local_map returned from a protocol driver’s
    bdrv_co_block_status() implementation is equal to the offset we
    passed to it (see comment there for why we should do this)

- Patch 3:
  - Add note why block drivers should return larger *pnum values in
    addition to just saying that it’s allowed


git-backport-diff against v2:

Key:
[----] : patches are identical
[####] : number of functional differences between upstream/downstream patch
[down] : patch is downstream-only
The flags [FC] indicate (F)unctional and (C)ontextual differences, respectively

001/6:[----] [--] 'block: Drop BDS comment regarding bdrv_append()'
002/6:[0063] [FC] 'block: block-status cache for data regions'
003/6:[0004] [FC] 'block: Clarify that @bytes is no limit on *pnum'
004/6:[----] [--] 'block/file-posix: Do not force-cap *pnum'
005/6:[----] [--] 'block/gluster: Do not force-cap *pnum'
006/6:[----] [--] 'block/iscsi: Do not force-cap *pnum'


Hanna Reitz (6):
  block: Drop BDS comment regarding bdrv_append()
  block: block-status cache for data regions
  block: Clarify that @bytes is no limit on *pnum
  block/file-posix: Do not force-cap *pnum
  block/gluster: Do not force-cap *pnum
  block/iscsi: Do not force-cap *pnum

 include/block/block_int.h | 61 +++++++++++++++++++++++++++--
 block.c                   | 80 +++++++++++++++++++++++++++++++++++++++
 block/file-posix.c        |  7 ++--
 block/gluster.c           |  7 ++--
 block/io.c                | 65 +++++++++++++++++++++++++++++--
 block/iscsi.c             |  3 --
 6 files changed, 207 insertions(+), 16 deletions(-)

-- 
2.31.1