Re: Unexpected behavior involving file attributes and snapshots.

[Roman Mamedov <rm@romanrm.net>]

On Tue, 14 Feb 2017 10:30:43 -0500
"Austin S. Hemmelgarn" <ahferroin7@gmail.com> wrote:

> I was just experimenting with snapshots on 4.9.0, and came across some 
> unexpected behavior.
> 
> The simple explanation is that if you snapshot a subvolume, any files in 
> the subvolume that have the NOCOW attribute will not have that attribute 
> in the snapshot.  Some further testing indicates that this is the only 
> file attribute that isn't preserved (I checked all the chattr flags that 
> BTRFS supports).
> 
> I'm kind of curious whether:
> 1. This is actually documented somewhere, as it's somewhat unexpected 
> given that everything else is preserved when snapshotting.
> 2. This is intended behavior, or just happens to be a side effect of the 
> implementation.

I don't seem to get this on 4.4.45 and 4.4.47.

$ btrfs sub create test
Create subvolume './test'
$ touch test/abc
$ chattr +C test/abc 
$ echo def > test/abc
$ ls -la test/abc 
-rw-r--r-- 1 rm rm 4 Feb 14 20:52 test/abc
$ lsattr test/abc 
---------------C test/abc
$ btrfs sub snap test test2
Create a snapshot of 'test' in './test2'
$ ls -la test2/abc 
-rw-r--r-- 1 rm rm 4 Feb 14 20:52 test2/abc
$ lsattr test2/abc 
---------------C test2/abc

-- 
With respect,
Roman