Re: [PATCH 13/26] block: move cache control settings out of queue->flags

[Damien Le Moal <dlemoal@kernel.org>]

On 6/17/24 15:04, Christoph Hellwig wrote:
> Move the cache control settings into the queue_limits so that the flags
> can be set atomically with the device queue frozen.
> 
> Add new features and flags field for the driver set flags, and internal
> (usually sysfs-controlled) flags in the block layer.  Note that we'll
> eventually remove enough field from queue_limits to bring it back to the
> previous size.
> 
> The disable flag is inverted compared to the previous meaning, which
> means it now survives a rescan, similar to the max_sectors and
> max_discard_sectors user limits.
> 
> The FLUSH and FUA flags are now inherited by blk_stack_limits, which
> simplified the code in dm a lot, but also causes a slight behavior
> change in that dm-switch and dm-unstripe now advertise a write cache
> despite setting num_flush_bios to 0.  The I/O path will handle this
> gracefully, but as far as I can tell the lack of num_flush_bios
> and thus flush support is a pre-existing data integrity bug in those
> targets that really needs fixing, after which a non-zero num_flush_bios
> should be required in dm for targets that map to underlying devices.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Acked-by: Ulf Hansson <ulf.hansson@linaro.org> [mmc]

A few nits below. With these fixed,

Reviewed-by: Damien Le Moal <dlemoal@kernel.org>

> +Implementation details for bio based block drivers
> +--------------------------------------------------
> +
> +For bio based drivers the REQ_PREFLUSH and REQ_FUA bit are simplify passed on

...bit are simplify... -> ...bits are simply...

> +to the driver if the drivers sets the BLK_FEAT_WRITE_CACHE flag and the drivers
> +needs to handle them.

s/drivers/driver (2 times)

> -and the driver must handle write requests that have the REQ_FUA bit set
> -in prep_fn/request_fn.  If the FUA bit is not natively supported the block
> -layer turns it into an empty REQ_OP_FLUSH request after the actual write.
> +When the BLK_FEAT_FUA flags is set, the REQ_FUA bit simplify passed on for the

s/bit simplify/bit is simply


-- 
Damien Le Moal
Western Digital Research