[Bug 1884831] Re: qemu-nbd fails to discard bigger chunks

[Thomas Huth <1884831@bugs.launchpad.net>]

The QEMU project is currently moving its bug tracking to another system.
For this we need to know which bugs are still valid and which could be
closed already. Thus we are setting older bugs to "Incomplete" now.

If the bug has already been fixed in the latest upstream version of QEMU,
then please close this ticket as "Fix released".

If it is not fixed yet and you think that this bug report here is still
valid, then you have two options:

1) If you already have an account on gitlab.com, please open a new ticket
for this problem in our new tracker here:

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

and then close this ticket here on Launchpad (or let it expire auto-
matically after 60 days). Please mention the URL of this bug ticket on
Launchpad in the new ticket on GitLab.

2) If you don't have an account on gitlab.com and don't intend to get
one, but still would like to keep this ticket opened, then please switch
the state back to "New" within the next 60 days (otherwise it will get
closed as "Expired"). We will then eventually migrate the ticket auto-
matically to the new system (but you won't be the reporter of the bug
in the new system and thus won't get notified on changes anymore).

Thank you and sorry for the inconvenience.


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

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https://bugs.launchpad.net/bugs/1884831

Title:
  qemu-nbd fails to discard bigger chunks

Status in QEMU:
  Incomplete

Bug description:
  This report is moved from systemd to here:
  https://github.com/systemd/systemd/issues/16242

  A qemu-nbd device reports that it can discard a lot of bytes:

  cat /sys/block/nbd0/queue/discard_max_bytes
  2199023255040

  And indeed, discard works with small images:

  $ qemu-img create -f qcow2 /tmp/image.img 2M
  $ sudo qemu-nbd --connect=/dev/nbd0 /tmp/image.img
  $ sudo blkdiscard /dev/nbd0

  but not for bigger ones (still smaller than discard_max_bytes):

  $ qemu-img create -f qcow2 /tmp/image.img 5G
  $ sudo qemu-nbd --connect=/dev/nbd0 /tmp/image.img
  $ sudo blkdiscard /dev/nbd0

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