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pc-bios/s390-ccw: Get Block Limits VPD device data

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The "Block Limits" Inquiry VPD page is optional for any SCSI device,
but if it's supported it provides a hint of the maximum I/O transfer
length for this particular device. If this page is supported by the
disk, let's issue that Inquiry and use the minimum of it and the
SCSI controller limit. That will cover this scenario:

  qemu-system-s390x ...
    -device virtio-scsi-ccw,id=scsi0,max_sectors=32768 ...
    -drive file=/dev/sda,if=none,id=drive0,format=raw ...
    -device scsi-hd,bus=scsi0.0,channel=0,scsi-id=0,
            drive=drive0,id=disk0,max_io_size=1048576

controller: 32768 sectors x 512 bytes/sector = 16777216 bytes
      disk:                                     1048576 bytes

Now that we have a limit for a virtio-scsi disk, compare that with the
limit for the virtio-scsi controller when we actually build the I/O.
The minimum of these two limits should be the one we use.

Signed-off-by: Eric Farman <farman@linux.vnet.ibm.com>
Message-Id: <20170510155359.32727-7-farman@linux.vnet.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
This commit is contained in:
Eric Farman 2017-05-10 17:53:57 +02:00 • committed by Cornelia Huck
parent 8edfe85bef
commit fe921fc8b7
3 changed files with 35 additions and 1 deletions
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1
pc-bios/s390-ccw/virtio.h
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@ -277,6 +277,7 @@ struct VDev {
bool scsi_device_selected;
ScsiDevice selected_scsi_device;
uint64_t netboot_start_addr;
uint32_t max_transfer;
};
typedef struct VDev VDev;