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Date:   Thu, 27 Jan 2022 04:37:33 +0000
From:   Matthew Wilcox <willy@infradead.org>
To:     Daniel Black <daniel@mariadb.org>
Cc:     linux-fsdevel@vger.kernel.org
Subject: Re: fcntl(fd, F_SETFL, O_DIRECT) succeeds followed by EINVAL in write
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On Thu, Jan 27, 2022 at 01:38:58PM +1100, Daniel Black wrote:
> > Sorry for the confusion.  You've caught us mid-transition.  Eventually,
> > ->direct_IO will be deleted, but for now it signifies whether or not the
> > filesystem supports O_DIRECT, even though it's not used (except in some
> > scenarios you don't care about).
> 
> being executed at the bottom of setfl which keeps the file descriptor
> out of O_DIRECT mode when
> the filesystem (like CIFS doesn't support it). In the original strace

Apparently I wasn't clear ...

CIFS absolutely does support O_DIRECT.  It does not do it by calling
->direct_IO; instead it's handled in cifs_loose_read_iter().