[Bug 1811543] Re: virtio-scsi gives improper discard sysfs entries

[Thomas Huth]

This is an automated cleanup. This bug report has been moved to QEMU's
new bug tracker on gitlab.com and thus gets marked as 'expired' now.
Please continue with the discussion here:

 https://gitlab.com/qemu-project/qemu/-/issues/161


** Changed in: qemu
       Status: New => Expired

** Bug watch added: gitlab.com/qemu-project/qemu/-/issues #161
   https://gitlab.com/qemu-project/qemu/-/issues/161

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https://bugs.launchpad.net/bugs/1811543

Title:
  virtio-scsi gives improper discard sysfs entries

Status in QEMU:
  Expired

Bug description:
  Apologies if this is just an inherent part of paravirtualization that
  should be expected.

  In my host, I have an LVM thin pool with chunk_size 128MB.  Within it,
  I have a thin volume "tmp".  In the host:

  # fdisk -l /dev/lvm/tmp
  Disk /dev/lvm/tmp: 256 MiB, 268435456 bytes, 524288 sectors
  Units: sectors of 1 * 512 = 512 bytes
  Sector size (logical/physical): 512 bytes / 4096 bytes
  I/O size (minimum/optimal): 262144 bytes / 134217728 bytes
  Disklabel type: gpt
  Disk identifier: BAE3154E-6E85-F642-8129-BAD7B58B2775

  Device        Start    End Sectors  Size Type
  /dev/lvm/tmp1  2048 524254  522207  255M Linux filesystem

  $ lsblk
  ...
        └─lvm-tmp                      254:13   0   256M  0 lvm
          └─lvm-tmp1                   254:14   0   255M  0 part

  $ cat /sys/dev/block/254:13/discard_alignment
  0
  $ cat /sys/dev/block/254:13/queue/discard_granularity
  134217728
  $ cat /sys/dev/block/254:13/queue/discard_max_bytes
  17179869184
  $ cat /sys/dev/block/254:13/queue/discard_max_hw_bytes
  0
  $ cat /sys/dev/block/254:13/queue/discard_zeroes_data
  0

  $ cat /sys/dev/block/254:14/discard_alignment
  133169152
  $ cat /sys/dev/block/254:14/queue/discard_granularity
  134217728
  $ cat /sys/dev/block/254:14/queue/discard_max_bytes
  17179869184
  $ cat /sys/dev/block/254:14/queue/discard_max_hw_bytes
  0
  $ cat /sys/dev/block/254:14/queue/discard_zeroes_data
  0

  If this is given to QEMU using virtio-scsi:

     -device virtio-scsi-pci,id=scsi1 \
     -drive 
driver=raw,node-name=hdb,file=/dev/lvm/tmp,if=none,discard=unmap,id=hd2 \
     -device scsi-hd,drive=hd2,bootindex=1 \

  Then incorrect values are given:

  $ lsblk
  ...
  sdb     8:16   0   256M  0 disk
  └─sdb1  8:17   0   255M  0 part /mnt

  $ cat /sys/dev/block/8:16/discard_alignment
  0
  $ cat /sys/dev/block/8:16/queue/discard_granularity
  4096
  $ cat /sys/dev/block/8:16/queue/discard_max_bytes
  1073741824
  $ cat /sys/dev/block/8:16/queue/discard_max_hw_bytes
  1073741824
  $ cat /sys/dev/block/8:16/queue/discard_zeroes_data
  0

  $ cat /sys/dev/block/8:17/discard_alignment
  133169152

  And, there isn't even a /sys/dev/block/8:17/queue direcotry.

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