linux-ext4 - Re: [PATCH] ext4: set FMODE_CAN_ODIRECT instead of a dummy direct

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Date:   Tue, 13 Jun 2023 07:47:00 +0200
From:   Christoph Hellwig <hch@....de>
To:     Ritesh Harjani <ritesh.list@...il.com>
Cc:     Christoph Hellwig <hch@....de>, tytso@....edu,
        linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: set FMODE_CAN_ODIRECT instead of a dummy
 direct_IO method

On Tue, Jun 13, 2023 at 11:00:19AM +0530, Ritesh Harjani wrote:
> why do we require .direct_IO function op for any of the dax_aops?
> IIUC, any inode if it supports DAX i.e. IS_DAX(inode), then it takes the
> separate path in file read/write iter path.
> 
> so it should never do ->direct_IO on an inode which supports DAX right?

do_dentry_open rejects opens with O_DIRECT if FMODE_CAN_ODIRECT is
not set.  So we either needs to set that manually or because there is a
->direct_IO if we want to keep supporting O_DIRECT opens for DAX
files, which we've traditionally supported.