[dm-devel] [PATCH v5 10/11] dm: introduce zone append emulation

[Hannes Reinecke]

On 5/25/21 11:25 PM, Damien Le Moal wrote:
> For zoned targets that cannot support zone append operations, implement
> an emulation using regular write operations. If the original BIO
> submitted by the user is a zone append operation, change its clone into
> a regular write operation directed at the target zone write pointer
> position.
> 
> To do so, an array of write pointer offsets (write pointer position
> relative to the start of a zone) is added to struct mapped_device. All
> operations that modify a sequential zone write pointer (writes, zone
> reset, zone finish and zone append) are intersepted in __map_bio() and
> processed using the new functions dm_zone_map_bio().
> 
> Detection of the target ability to natively support zone append
> operations is done from dm_table_set_restrictions() by calling the
> function dm_set_zones_restrictions(). A target that does not support
> zone append operation, either by explicitly declaring it using the new
> struct dm_target field zone_append_not_supported, or because the device
> table contains a non-zoned device, has its mapped device marked with the
> new flag DMF_ZONE_APPEND_EMULATED. The helper function
> dm_emulate_zone_append() is introduced to test a mapped device for this
> new flag.
> 
> Atomicity of the zones write pointer tracking and updates is done using
> a zone write locking mechanism based on a bitmap. This is similar to
> the block layer method but based on BIOs rather than struct request.
> A zone write lock is taken in dm_zone_map_bio() for any clone BIO with
> an operation type that changes the BIO target zone write pointer
> position. The zone write lock is released if the clone BIO is failed
> before submission or when dm_zone_endio() is called when the clone BIO
> completes.
> 
> The zone write lock bitmap of the mapped device, together with a bitmap
> indicating zone types (conv_zones_bitmap) and the write pointer offset
> array (zwp_offset) are allocated and initialized with a full device zone
> report in dm_set_zones_restrictions() using the function
> dm_revalidate_zones().
> 
> For failed operations that may have modified a zone write pointer, the
> zone write pointer offset is marked as invalid in dm_zone_endio().
> Zones with an invalid write pointer offset are checked and the write
> pointer updated using an internal report zone operation when the
> faulty zone is accessed again by the user.
> 
> All functions added for this emulation have a minimal overhead for
> zoned targets natively supporting zone append operations. Regular
> device targets are also not affected. The added code also does not
> impact builds with CONFIG_BLK_DEV_ZONED disabled by stubbing out all
> dm zone related functions.
> 
> Signed-off-by: Damien Le Moal <damien.lemoal at wdc.com>
> Reviewed-by: Himanshu Madhani <himanshu.madhani at oracle.com>
> ---
>   drivers/md/dm-core.h          |  13 +
>   drivers/md/dm-table.c         |  19 +-
>   drivers/md/dm-zone.c          | 580 ++++++++++++++++++++++++++++++++--
>   drivers/md/dm.c               |  38 ++-
>   drivers/md/dm.h               |  16 +-
>   include/linux/device-mapper.h |   6 +
>   6 files changed, 618 insertions(+), 54 deletions(-)
> 
Reviewed-by: Hannes Reinecke <hare at suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare at suse.de                              +49 911 74053 688
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