Improve zvol creation error handling
Description
Problem/Justification
Impact
SmartDraw Connector
Katalon Manual Tests (BETA)
Activity
Alexander Motin July 15, 2021 at 3:10 PM
This PR should fix it: https://github.com/openzfs/zfs/pull/12375
Alexander Motin July 15, 2021 at 1:30 PM
I've reproduced this. But as I have thought, reboot (or probably pool export/import too) fixes the issue – /dev/zvol/tank/short appears, so recreation is not required, though could be done if there is nothing on that zvol. It seems in case of the error zvol appears in some half-created state, when later rename does not work. Reboot or pool re-import fixes that.
David Durrleman July 14, 2021 at 10:11 PM
Following your nomenclature, here's the behaviour I describe
As you can see, /dev/zvol/tank/short doesn't exist even though tank/short is obviously less than 65 characters. If I had created tank/short directly, everything would have been fine, but because it was a rename of a zvol with a long name, the issue persists. The problem is that the error message one would get in the UI (Disk path /dev/zvol/tank/long123456789012345678901234567890123456789012345678901234567890 is too long, reduce to less than 63 characters) suggests to the user that renaming the zvol will fix the issue, whereas in fact it doesn't help at all.
I see three potential fixes, two I had mentioned earlier
change the error message to say "create a new zvol with a shorter name (don't rename this one, it won't work)"
or, support zvols that were created with a long name and renamed to a shorter one
But another alternative would also help
emit an error immediately when the user creates a zvol with a long name (and prevent the zvol from being created altogether), instead of at VM creation time.
This now being the second time I rephrase this issue, I hope I was able to be clear because I am not sure how I can do better.
Alexander Motin July 9, 2021 at 2:19 AM
I've tried it on 12.0-U2.1, for which I had a boot environment, and it worked fine too:
Wasn't your VM running while you was trying to rename it by chance?
Alexander Motin July 9, 2021 at 2:11 AM
The limitation of 63 symbols unfortunate is unavoidable for FreeBSD 12 and respectively TrueNAS 12. In 13 it finally will be 255.
What's about the rename, I just tested it on my 12.0-U4 VM:
So seems like it is working. Either it was fixed, or what am I doing wrong? Could you try to update and retry?
Follow up to as requested
When creating a VM based on the clone of an existing ZVol's snapshot, and that clone's name is too long (which is likely the case with the default naming suggestion), one gets the following error message:
[ENOENT] vm_create.devices.1.attributes.path: Disk path /dev/zvol/<redacted-long-name> does not exist. [ENAMETOOLONG] vm_create.devices.1.attributes.path: Disk path /dev/zvol/<redacted-long-name> is too long, reduce to less than 63 characters
This error message is misleading. In the UI, it's not possible to rename an existing ZVol. It's possible to do so in the shell, e.g.
zfs rename <redacted-long-name> <redacted-short-name>
But unfortunately, this does not create the necessary entry under /dev/zvol
So if you try to recreate the VM, using the now shortened name, as advised by the original error message, you now get this error:
[ENOENT] vm_create.devices.1.attributes.path: Disk path /dev/zvol/<redacted-short-name> does not exist.
The only way to actually create the VM as intended, is to make sure that when you clone the original snapshot, you set a short name there. But at that point, there is no reason to know that this will be important later.