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Message-ID: <b902bee1-fcfd-4542-8a4e-c6b9861828c9@oracle.com>
Date: Wed, 14 Feb 2024 12:36:40 +0000
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Subject: Re: [PATCH 6/6] fs: xfs: Set FMODE_CAN_ATOMIC_WRITE for
 FS_XFLAG_ATOMICWRITES set
Content-Language: en-US
To: "Darrick J. Wong" <djwong@kernel.org>
Cc: hch@lst.de, viro@zeniv.linux.org.uk, brauner@kernel.org,
        dchinner@redhat.com, jack@suse.cz, chandan.babu@oracle.com,
        martin.petersen@oracle.com, linux-kernel@vger.kernel.org,
        linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        tytso@mit.edu, jbongio@google.com, ojaswin@linux.ibm.com
References: <20240124142645.9334-1-john.g.garry@oracle.com>
 <20240124142645.9334-7-john.g.garry@oracle.com>
 <20240202180619.GK6184@frogsfrogsfrogs>
 <7e3b9556-f083-4c14-a48f-46242d1c744b@oracle.com>
 <20240213175954.GV616564@frogsfrogsfrogs>
From: John Garry <john.g.garry@oracle.com>
Organization: Oracle Corporation
In-Reply-To: <20240213175954.GV616564@frogsfrogsfrogs>
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On 13/02/2024 17:59, Darrick J. Wong wrote:
>>> Shouldn't we check that the device supports AWU at all before turning on
>>> the FMODE flag?
>> Can we easily get this sort of bdev info here?
>>
>> Currently if we do try to issue an atomic write and AWU for the bdev is
>> zero, then XFS iomap code will reject it.
> Hmm.  Well, if we move towards pushing all the hardware checks out of
> xfs/iomap and into whatever goes on underneath submit_bio then I guess
> we don't need to check device support here at all.

Yeah, I have been thinking about this. But I was still planning on 
putting a "bdev on atomic write" check here, as you mentioned.

But is this a proper method to access the bdev for an xfs inode:

STATIC bool
xfs_file_can_atomic_write(
struct xfs_inode *inode)
{
	struct xfs_buftarg *target = xfs_inode_buftarg(inode);
	struct block_device *bdev = target->bt_bdev;

	if (!xfs_inode_atomicwrites(inode))
		return false;

	return bdev_can_atomic_write(bdev);
}

I do notice the dax check in xfs_bmbt_to_iomap() when assigning 
iomap->bdev, which is creating some doubt?

Thanks,
John