Messages in this thread | | | Subject | Re: LVM snapshot broke between 4.14 and 4.16 | From | WGH <> | Date | Fri, 3 Aug 2018 00:32:21 +0300 |
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On 08/02/2018 09:32 PM, Linus Torvalds wrote: > WGH (sorry, no idea what your real name is) - what's the source of the > script that broke? Was it some system script you got from outside and > likely to affect others too? > > Or was it just some local thing you wrote yourself and was > unintentionally buggy and nobody else is likely to hit this? > > Because if the latter, if you can work around it and you're the only > user this hits, we might just be able to ignore it.
The script in question is written by me and contains literally two lines:
lvcreate --size 5G --snapshot --name snap0 --permission r /dev/mapper/vg0-lvol_rootfs mount /dev/mapper/vg0-snap0 /mnt/rootfs_snapshot
The script is not buggy (I think), it was written under simple assumption that --permission r works. And it does - unless you happen to have combination of kernel >=4.16 and lvm2 <2.02.178.
The commit in question appeared only in 4.16, and this kernel version is not widespread yet. You have to be running both recent kernel and not-so-recent lvm2 to be bitten by this. This probably explains why no one else reported this problem.
Workaround certainly exists: I can just create read-write snapshot, but mount it read-only. The reason why I didn't discover the workaround earlier is that after unsuccessful read-only snapshot creation system ends up in some weird state where read-write snapshots are also failing with the same error (until reboot). So I got a wrong impression that read-write snapshots were broken as well.
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