Re: [Patch v9 09/10] scsi: scsi_debug: Atomic write support

[Hannes Reinecke]

On 6/20/24 14:53, John Garry wrote:
> Add initial support for atomic writes.
>
> As is standard method, feed device properties via modules param, those
> being:
> - atomic_max_size_blks
> - atomic_alignment_blks
> - atomic_granularity_blks
> - atomic_max_size_with_boundary_blks
> - atomic_max_boundary_blks
>
> These just match sbc4r22 section 6.6.4 - Block limits VPD page.
>
> We just support ATOMIC WRITE (16).
>
> The major change in the driver is how we lock the device for RW accesses.
>
> Currently the driver uses a per-device lock for accessing device metadata
> and "media" data (calls to do_device_access()) atomically for the duration
> of the whole read/write command.
>
> This should not suit verifying atomic writes. Reason being that currently
> all reads/writes are atomic, so using atomic writes does not prove
> anything.
>
> Change device access model to basis that regular writes only atomic on a
> per-sector basis, while reads and atomic writes are fully atomic.
>
> As mentioned, since accessing metadata and device media is atomic,
> continue to have regular writes involving metadata - like discard or PI -
> as atomic. We can improve this later.
>
> Currently we only support model where overlapping going reads or writes
> wait for current access to complete before commencing an atomic write.
> This is described in 4.29.3.2 section of the SBC. However, we simplify,
> things and wait for all accesses to complete (when issuing an atomic
> write).
>
> Reviewed-by: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
> Signed-off-by: John Garry <john.g.garry@xxxxxxxxxx>
> ---
>   drivers/scsi/scsi_debug.c | 588 +++++++++++++++++++++++++++++---------
>   1 file changed, 454 insertions(+), 134 deletions(-)
Reviewed-by: Hannes Reinecke <hare@xxxxxxx>

Cheers,

Hannes
--
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@xxxxxxx                                +49 911 74053 688
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