Re: [Qemu-devel] [PATCH v3 0/5] Geometry and blocksize detection for backing devices.

[Ekaterina Tumanova <tumanova@linux.vnet.ibm.com>]

On 12/05/2014 08:56 PM, Ekaterina Tumanova wrote:
> This 3rd revision of the patch set.
>
> Proper geometry and blocksize information is vital for support of
> DASD/ECKD drives in Linux guests. Otherwise things will fail in
> certain cases.
>
> The existing geometry and blocksize qemu defaults have no sense
> for DASD drives (hd_geometry_guess detection and 512 for sizes).
> Setting this information manually in XML file is far from user-friendly,
> as the admin has to manually look up the properties of the
> host disks and then modify the guest definition accordingly.
>
> Since Linux uses DASDs as normal block devices, we actually
> want to use virtio-blk to pass those to KVM guests.
>
> In order to avoid any change in behavior of other drives, the DASD
> special casing was advised. We call ioctl BIODASDINFO2 on the block
> device, which will only succeed if the device is really a DASD.
>
> In order to retrieve the underlying device geometry and blocksizes
> a new block-backend functions and underlying driver functions were
> introduced (blk_probe_blocksizes anf blk_probe_geometry wrappers
> and corresponding bdrv_xxxxxx functions).
>
> As for now only "host_device" driver received new detection methods.
> For "raw" we call childs method as usual. In future one may update
> other drivers to add some other detection heuristics.
>
> If the host_device appears to be a DASD, the driver functions
> (hdev_probe_blocksizes and hdev_probe_geometry) will call certain
> ioctls in order to detect geometry and blocksizes of the underlying device.
> if probing failed bdrv_probe_blocksizes caller will set defaults,
> and bdrv_probe_geometry will fail to allow fallback to old detection logic.
>
> The front-end (BlockConf API) was updated:
> 1. a new blkconf_blocksizes function was added. It doesn't
> change user-defined blocksize values. If properties are unset, it will
> set values, returned by blk_probe_backend. In order to allow this logic,
> blocksize properties were initialized with 0. (driver will return 512 if
> backing device probing didn't succeed or if driver method is not defined).
> 2. hd_geometry guess was changed to firstly try to retrieve values via
> blk_probe_geometry and if it fails, fallback to the old logic.
>
> updates from v2:
> - avoid passing structs as a function result in backend part
> - fix patch desctiptions
> - add the blkconf_blocksizes call to all the users of BlockConf
> - do not change geometry and blocksize values set via command-line, to do that:
> remove hardcoding 512 in DEFINE_BLOCK_PROPERTIES. set defaults in
> blk_probe_blocksizes (now always succeeds) and call it only if property is 0.
> - fix cylinders calculation.
> - document blk_probe_geometry call as "currently only for DASD".
> - anything I forgot :)
>
> Ekaterina Tumanova (5):
>    block: add bdrv functions for geometry and blocksize
>    raw-posix: Factor block size detection out of raw_probe_alignment()
>    block: Add driver methods to probe blocksizes and geometry
>    block-backend: Add wrappers for blocksizes and geometry probing
>    BlockConf: Call backend functions to detect geometry and blocksizes
>
>   block.c                        |  35 +++++++++++
>   block/block-backend.c          |  10 +++
>   block/raw-posix.c              | 135 +++++++++++++++++++++++++++++++++++------
>   block/raw_bsd.c                |  14 +++++
>   hw/block/block.c               |  18 ++++++
>   hw/block/hd-geometry.c         |  12 ++++
>   hw/block/nvme.c                |   1 +
>   hw/block/virtio-blk.c          |   1 +
>   hw/core/qdev-properties.c      |   3 +-
>   hw/ide/qdev.c                  |   1 +
>   hw/scsi/scsi-disk.c            |   1 +
>   hw/usb/dev-storage.c           |   1 +
>   include/block/block.h          |  13 ++++
>   include/block/block_int.h      |   5 ++
>   include/hw/block/block.h       |   5 +-
>   include/sysemu/block-backend.h |   2 +
>   16 files changed, 237 insertions(+), 20 deletions(-)
>

friendly *ping* to maintainers of block layer :) I would rather not send 
next version without getting your feedback first.