diff options
| author | Andrey Shinkevich <andrey.shinkevich@virtuozzo.com> | 2020-12-16 09:16:58 +0300 |
|---|---|---|
| committer | Max Reitz <mreitz@redhat.com> | 2021-01-26 14:36:37 +0100 |
| commit | e275458b29b7040a388ca46af094b0602c769ef1 (patch) | |
| tree | 713c8753f608579d3e08bd138e92ce322a0c9059 /include | |
| parent | 897dd0ec4fdea4e6fa7674729750d05acc1bf41e (diff) | |
copy-on-read: skip non-guest reads if no copy needed
If the flag BDRV_REQ_PREFETCH was set, skip idling read/write
operations in COR-driver. It can be taken into account for the
COR-algorithms optimization. That check is being made during the
block stream job by the moment.
Add the BDRV_REQ_PREFETCH flag to the supported_read_flags of the
COR-filter.
block: Modify the comment for the flag BDRV_REQ_PREFETCH as we are
going to use it alone and pass it to the COR-filter driver for further
processing.
Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20201216061703.70908-9-vsementsov@virtuozzo.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
Diffstat (limited to 'include')
| -rw-r--r-- | include/block/block.h | 8 |
1 files changed, 5 insertions, 3 deletions
diff --git a/include/block/block.h b/include/block/block.h index 127bdf3392..81fcaad5ac 100644 --- a/include/block/block.h +++ b/include/block/block.h @@ -72,9 +72,11 @@ typedef enum { BDRV_REQ_NO_FALLBACK = 0x100, /* - * BDRV_REQ_PREFETCH may be used only together with BDRV_REQ_COPY_ON_READ - * on read request and means that caller doesn't really need data to be - * written to qiov parameter which may be NULL. + * BDRV_REQ_PREFETCH makes sense only in the context of copy-on-read + * (i.e., together with the BDRV_REQ_COPY_ON_READ flag or when a COR + * filter is involved), in which case it signals that the COR operation + * need not read the data into memory (qiov) but only ensure they are + * copied to the top layer (i.e., that COR operation is done). */ BDRV_REQ_PREFETCH = 0x200, |