linux-kernel - Re: [PATCH 3/6] fs: xfs: Support FS_XFLAG

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Date: Wed, 14 Feb 2024 12:19:11 +0000
From: John Garry <john.g.garry@...cle.com>
To: "Darrick J. Wong" <djwong@...nel.org>
Cc: hch@....de, viro@...iv.linux.org.uk, brauner@...nel.org,
        dchinner@...hat.com, jack@...e.cz, chandan.babu@...cle.com,
        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
Subject: Re: [PATCH 3/6] fs: xfs: Support FS_XFLAG_ATOMICWRITES for rtvol

On 13/02/2024 17:22, Darrick J. Wong wrote:
>> I am not sure what bdev_validate_atomic_write() would even do. If
>> sb_rextsize exceeded the bdev atomic write unit max, then we just cap
>> reported atomic write unit max in statx to that which the bdev reports and
>> vice-versa.
>>
>> And didn't we previously have a concern that it is possible to change the
>> geometry of the device?
> The thing is, I don't want this logic:
> 
> 	if (!is_power_of_2(mp->m_sb.sb_rextsize))
> 		/* fail */

This is really specific to XFS. Let's see where all this alignment stuff 
goes before trying to unify all these checks.

> 
> to be open-coded inside xfs.  I'd rather have a standard bdev_* helper
> that every filesystem can call, so we don't end up with more generic
> code copy-pasted all over the codebase.
> 
> The awkward part (for me) is the naming, since filesystems usually don't
> have to check with the block layer about their units of space allocation.
> 
> /*
>   * Ensure that a file space allocation unit is congruent with the atomic
>   * write unit capabilities of supported block devices.
>   */
> static inline bool bdev_validate_atomic_write_allocunit(unsigned au)
> {
> 	return is_power_of_2(au);
> }
> 
> 	if (!bdev_validate_atomic_write_allocunit(mp->m-sb.sb_rextsize))
> 		return -EINVAL;

As above, I can try to unify, but this alignment stuff is a bit up in 
the air at the moment.

Thanks,
John