From: Roman Mamedov <rm@romanrm.net>
To: Brian Hansen <dulanic@gmail.com>
Cc: linux-btrfs@vger.kernel.org
Subject: reflink copy now works with nocow?
Date: Sat, 2 Nov 2019 19:36:24 +0500 [thread overview]
Message-ID: <20191102193624.3411de0d@natsu> (raw)
In-Reply-To: <CAMiuOHXH1ic6Mcz+o1uWLNMCK+iCinhR+nnZ8N1wTHQoEms-7Q@mail.gmail.com>
On Sat, 2 Nov 2019 08:49:37 -0500
Brian Hansen <dulanic@gmail.com> wrote:
> Hello,
>
> First time i've sent to this group but I am trying to figure out the
> cause of this. Normal copy is working fine, but then if I use
> --reflink it says invalid argument. Not sure how to read some of this,
> but here is the strace.
>
> I'm running kernel v4.15
>
> Here is the full output of strace. I ran a strace on normal copy and
> most looks similar so I'm not able to figure out much here...
>
> https://pastebin.com/raw/YmQ8FvCH
At first I was going to say, "oh it's because you are using 'chattr +C', or
mounted the filesystem as nocow, and reflink copying is prevented by those".
In fact this article from 2014 confirms that to be the case:
http://infotinks.com/btrfs-nodatacow-reflink-copies-snapshots/
But then I tested on my machine, and what used to fail, now works:
# mkdir tmp
# chattr +C tmp
# echo abc > tmp/a
# cp -a --reflink=always tmp/a tmp/b
# lsattr tmp/
----------------C-- tmp/a
----------------C-- tmp/b
According to strace, the clone IOCTL succeeds:
...
openat(AT_FDCWD, "tmp/b", O_WRONLY|O_CREAT|O_EXCL, 0600) = 4
fstat(4, {st_mode=S_IFREG|0600, st_size=0, ...}) = 0
ioctl(4, BTRFS_IOC_CLONE or FICLONE, 3) = 0
...
Same on kernels 4.14.151, 4.14.113 and 4.9.189.
So I wonder, is setting nocow via 'chattr +C' getting ignored now, or is there
an improvement that it no longer prevents reflink copying?
--
With respect,
Roman
next prev parent reply other threads:[~2019-11-02 14:36 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-02 13:49 cp --reflink invalid argument error Brian Hansen
2019-11-02 14:36 ` Roman Mamedov [this message]
2019-11-02 15:09 ` reflink copy now works with nocow? Brian Hansen
2019-11-02 15:24 ` Roman Mamedov
2019-11-02 20:15 ` Brian Hansen
2019-11-14 5:21 ` Zygo Blaxell
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