Re: [Qemu-devel] [PATCH v4 0/5] Geometry and blocksize detection for backing devices.

[Christian Borntraeger <borntraeger@de.ibm.com>]

Am 16.12.2014 um 12:10 schrieb Ekaterina Tumanova:
> Updates:
> v2 -> v3:
> 1. Fix comments
> 2. Fix error codes to -ENOTSUP.
> 3. Reduce LOC in probe_logical_blocksize.
> 4. Adjust #ifdef - #else logic in couple of places.
> 5. Rebased.
> 
> I hope that I addressed all the comments from the last round of review.
> If you think it's ok now, can you please give me your explicit Review-by.
> (I would really appreciate if you could give me some feedback this week,
> because I'm leaving for vacation next week)
> 
> Looking forward to your reply,
> Thanks a lot!
> Kate.
> ---------------------------------------------------------------
>    Patchset Description (didn't change):
> 
> 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.
> 
> 
> 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                        |  34 ++++++++++
>  block/block-backend.c          |  10 +++
>  block/raw-posix.c              | 138 ++++++++++++++++++++++++++++++++++++-----
>  block/raw_bsd.c                |  14 +++++
>  hw/block/block.c               |  15 +++++
>  hw/block/hd-geometry.c         |  10 ++-
>  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      |  15 +++++
>  include/hw/block/block.h       |   5 +-
>  include/sysemu/block-backend.h |   2 +
>  16 files changed, 243 insertions(+), 21 deletions(-)
> 

I can confirm that this patch still works for my DASDs.

Christian