linux-kernel - Re: [PATCH 0/6] block atomic writes for XFS

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Date: Tue, 13 Feb 2024 13:15:29 +0530
From: Ritesh Harjani (IBM) <ritesh.list@...il.com>
To: John Garry <john.g.garry@...cle.com>, hch@....de, djwong@...nel.org, viro@...iv.linux.org.uk, brauner@...nel.org, dchinner@...hat.com, jack@...e.cz, chandan.babu@...cle.com
Cc: martin.petersen@...cle.com, linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org, tytso@....edu, jbongio@...gle.com, ojaswin@...ux.ibm.com, John Garry <john.g.garry@...cle.com>
Subject: Re: [PATCH 0/6] block atomic writes for XFS

John Garry <john.g.garry@...cle.com> writes:

> This series expands atomic write support to filesystems, specifically
> XFS. Since XFS rtvol supports extent alignment already, support will
> initially be added there. When XFS forcealign feature is merged, then we
> can similarly support atomic writes for a non-rtvol filesystem.
>
> Flag FS_XFLAG_ATOMICWRITES is added as an enabling flag for atomic writes.
>
> For XFS rtvol, support can be enabled through xfs_io command:
> $xfs_io -c "chattr +W" filename
> $xfs_io -c "lsattr -v" filename
> [realtime, atomic-writes] filename

Hi John,

I first took your block atomic write patch series [1] and then applied this
series on top. I also compiled xfsprogs with chattr atomic write support from [2]. 

[1]: https://lore.kernel.org/linux-nvme/20240124113841.31824-1-john.g.garry@oracle.com/T/#m4ad28b480a8e12eb51467e17208d98ca50041ff2
[2]: https://github.com/johnpgarry/xfsprogs-dev/commits/atomicwrites/


But while setting +W attr, I see an Invalid argument error. Is there
anything I need to do first?

root@...ntu:~# /root/xt/xfsprogs-dev/io/xfs_io -c "chattr +W" /mnt1/test/f1
xfs_io: cannot set flags on /mnt1/test/f1: Invalid argument

root@...ntu:~# /root/xt/xfsprogs-dev/io/xfs_io -c "lsattr -v" /mnt1/test/f1
[realtime] /mnt1/test/f1

>
> The FS needs to be formatted with a specific extent alignment size, like:
> mkf.xfs -r rtdev=/dev/sdb,extsize=16K -d rtinherit=1 /dev/sda
>
> This enables 16K atomic write support. There are no checks whether the
> underlying HW actually supports that for enabling atomic writes with
> xfs_io, though, so statx needs to be issued for a file to know atomic
> write limits.
>

Here you say that xfs_io does not check whether underlying HW actually
supports atomic writes or not. So I am assuming xfs_io -c "chattr +W"
should have just worked?

Sorry, I am still in the process of going over the patches, but I thought let
me anyways ask this first.


-ritesh