linux-ext4 - Re: [RFC PATCH v4 07/11] fs: statx add write zeroes unmap attribute

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Message-ID: <20250505142945.GJ1035866@frogsfrogsfrogs>
Date: Mon, 5 May 2025 07:29:45 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: Christoph Hellwig <hch@....de>
Cc: Zhang Yi <yi.zhang@...weicloud.com>, linux-fsdevel@...r.kernel.org,
	linux-ext4@...r.kernel.org, linux-block@...r.kernel.org,
	dm-devel@...ts.linux.dev, linux-nvme@...ts.infradead.org,
	linux-scsi@...r.kernel.org, linux-xfs@...r.kernel.org,
	linux-kernel@...r.kernel.org, tytso@....edu,
	john.g.garry@...cle.com, bmarzins@...hat.com, chaitanyak@...dia.com,
	shinichiro.kawasaki@....com, brauner@...nel.org,
	yi.zhang@...wei.com, chengzhihao1@...wei.com, yukuai3@...wei.com,
	yangerkun@...wei.com
Subject: Re: [RFC PATCH v4 07/11] fs: statx add write zeroes unmap attribute

On Mon, May 05, 2025 at 03:22:08PM +0200, Christoph Hellwig wrote:
> On Mon, Apr 21, 2025 at 10:15:05AM +0800, Zhang Yi wrote:
> > From: Zhang Yi <yi.zhang@...wei.com>
> > 
> > Add a new attribute flag to statx to determine whether a bdev or a file
> > supports the unmap write zeroes command.
> > 
> > Signed-off-by: Zhang Yi <yi.zhang@...wei.com>
> > ---
> >  block/bdev.c              | 4 ++++
> >  fs/ext4/inode.c           | 9 ++++++---
> >  include/uapi/linux/stat.h | 1 +
> >  3 files changed, 11 insertions(+), 3 deletions(-)
> > 
> > diff --git a/block/bdev.c b/block/bdev.c
> > index 4844d1e27b6f..29b0e5feb138 100644
> > --- a/block/bdev.c
> > +++ b/block/bdev.c
> > @@ -1304,6 +1304,10 @@ void bdev_statx(struct path *path, struct kstat *stat,
> >  			queue_atomic_write_unit_max_bytes(bd_queue));
> >  	}
> >  
> > +	if (bdev_write_zeroes_unmap(bdev))
> > +		stat->attributes |= STATX_ATTR_WRITE_ZEROES_UNMAP;
> > +	stat->attributes_mask |= STATX_ATTR_WRITE_ZEROES_UNMAP;
> 
> Hmm, shouldn't this always be set by stat?  But I might just be
> really confused what attributes_mask is, and might in fact have
> misapplied it in past patches of my own..

attributes_mask contains attribute flags known to the filesystem,
whereas attributes contains flags actually set on the file.
"known_attributes" would have been a better name, but that's water under
the bridge. :P

> Also shouldn't the patches to report the flag go into the bdev/ext4
> patches that actually implement the feature for the respective files
> to keep bisectability?

/I/ think so...

--D