Re: [PATCH 05/13] block: Export I/O topology for block devices and partitions

[Jens Axboe <jens.axboe@oracle.com>]

On Fri, May 15 2009, Martin K. Petersen wrote:
> From: Martin K. Petersen <martin.petersen@oracle.com>
> 
> To support devices with physical block sizes bigger than 512 bytes we
> need to ensure proper alignment.  This patch adds support for exposing
> I/O topology characteristics as devices are stacked.
> 
>   logical_block_size is the smallest unit the device can address.
> 
>   physical_block_size indicates the smallest I/O the device can write
>   without incurring a read-modify-write penalty.
> 
>   The io_min parameter is the smallest preferred I/O size reported by
>   the device.  In many cases this is the same as the physical block
>   size.  However, the io_min parameter can be scaled up when stacking
>   (RAID5 chunk size > physical block size).
> 
>   The io_opt characteristic indicates the optimal I/O size reported by
>   the device.  This is usually the stripe width for arrays.
> 
>   The io_alignment parameter indicates the number of bytes the start of
>   the device/partition is offset from the device's natural alignment.
>   Partition tools and MD/DM utilities can use this to pad their offsets
>   so filesystem start on proper boundaries.
> 
> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
> ---
>  Documentation/ABI/testing/sysfs-block |   59 +++++++++++
>  block/blk-settings.c                  |  184 +++++++++++++++++++++++++++++++++
>  block/blk-sysfs.c                     |   33 ++++++
>  block/genhd.c                         |   10 ++
>  fs/partitions/check.c                 |   10 ++
>  include/linux/blkdev.h                |   47 +++++++++
>  include/linux/genhd.h                 |    1 +
>  7 files changed, 344 insertions(+), 0 deletions(-)
> 
> diff --git a/Documentation/ABI/testing/sysfs-block b/Documentation/ABI/testing/sysfs-block
> index 44f52a4..93075cf 100644
> --- a/Documentation/ABI/testing/sysfs-block
> +++ b/Documentation/ABI/testing/sysfs-block
> @@ -60,3 +60,62 @@ Description:
>  		Indicates whether the block layer should automatically
>  		generate checksums for write requests bound for
>  		devices that support receiving integrity metadata.
> +
> +What:		/sys/block/<disk>/alignment
> +Date:		April 2009
> +Contact:	Martin K. Petersen <martin.petersen@oracle.com>
> +Description:
> +		Storage devices may report a physical block size that is
> +		bigger than the logical block size (for instance a drive
> +		with 4KB physical sectors exposing 512-byte logical
> +		blocks to the operating system).  This parameter
> +		indicates how many bytes the beginning of the device is
> +		offset from the disk's natural alignment.
> +
> +What:		/sys/block/<disk>/<partition>/alignment
> +Date:		April 2009
> +Contact:	Martin K. Petersen <martin.petersen@oracle.com>
> +Description:
> +		Storage devices may report a physical block size that is
> +		bigger than the logical block size (for instance a drive
> +		with 4KB physical sectors exposing 512-byte logical
> +		blocks to the operating system).  This parameter
> +		indicates how many bytes the beginning of the partition
> +		is offset from the disk's natural alignment.

I really hate the 'alignment' name, nobody will know wtf that is without
looking it up. The rest of the names are fairly self explanatory.
offset? offset_size? misalignment? Not very good with names, but perhaps
we can find something more appropriate :-)

The rest of the patch set looks ok to me, if we can just agree on a
silly name, then lets merge it for 2.6.31.

-- 
Jens Axboe