On 19/6/2014 12:22 πμ, Duncan wrote:
Konstantinos Skarlatos posted on Wed, 18 Jun 2014 16:23:04 +0300 as
excerpted:
I guess that btrfs developers have put these BUG_ONs so that they get
reports from users when btrfs gets in these unexpected situations. But
if most of these reports are ignored or not resolved, then maybe there
is no use for these BUG_ONs and they should be replaced with something
more mild.
Keep in mind that if a system panics, then the only way to get logs from
it is with serial or netconsole, so BUG_ON really makes it much harder
for users to know what happened and send reports, and only the most
technical and determined users will manage to send reports here.
In terms of the BUGONs, they've been converting them to WARNONs recently,
exactly due to the point you and Marc have made. Not being a dev and
simply based on the patch-flow I've seen as btrfs has been basically
behaving itself so far here[1], I had /thought/ that was more or less
done (perhaps some really bad bug-ons left but only a few, and basically
only where the kernel couldn't be sure it was in a logical enough state
to continue writing to other filesystems too, so bugon being logical in
that case), but based on you guys' comments there's apparently more to go.
So at least for BUGONs they agree. I guess it's simply a matter of
getting them all converted.
Thats good to hear. But we should have a way to recover from these kinds
of problems, first of all having btrfs report the exact location, disk
and file name that is affected, and then make scrub fix or at least
report about it, and finaly make fsck work for this.
My filesystem that consistently kernel panics when a specific logical
address is read, passes scrub without anything bad reported. What's the
use of scrub if it cant deal with this?
Tho at least in Marc's case, he's running kernels a couple back in some
cases and they may still have BUGONs already replaced in the most current
kernel.
As for experimental, they've been toning down and removing the warnings
recently. Yes, the on-device format may come with some level of
compatibility guarantee now so I do agree with that bit, but IMO anyway,
that warning should be being replaced with a more explicit "on-device-
format is now stable but the code is not yet entirely so, so keep your
backups and be prepared to use them, and run current kernels", language,
and that's not happening, they're mostly just toning it down without the
still explicit warnings, ATM.
---
[1] Btrfs (so far) behaving itself here: Possibly because my filesystems
are relatively small and I don't use snapshots much and prefer several
smaller independent filesystems rather than doing subvolumes, thus
keeping the number of eggs in a single basket small. Plus, with small
filesystems on SSD, I can balance reasonably regularly, and I do full
fresh mkfs.btrfs rounds every few kernels as well to take advantage of
newer features, which may well have the result of killing smaller
problems that aren't yet showing up before they get big enough to cause
real issues. Anyway, I'm not complaining! =:^)
Well my use case is about 25 filesystems on rotating disks, 20 of them
on single disks, and the rest are multiple disk filesystems, either
raid1 or single. I have many subvolumes and in some cases thousands of
snapshots, but no databases, systemd and the like on them. Of course I
have everything backed up, </nag mode on> but I believe that after all
those years of development I shouldnt still be forced to do mkfs every 6
monts or so, when i use no new features. </nag mode off>
--
Konstantinos Skarlatos
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