From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ot0-f194.google.com ([74.125.82.194]:44808 "EHLO mail-ot0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754037AbeFKIIb (ORCPT ); Mon, 11 Jun 2018 04:08:31 -0400 Received: by mail-ot0-f194.google.com with SMTP id w13-v6so22721868ote.11 for ; Mon, 11 Jun 2018 01:08:31 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20180610053128.GO30522@ZenIV.linux.org.uk> References: <20180529144339.16538-1-mszeredi@redhat.com> <20180529144339.16538-24-mszeredi@redhat.com> <20180610053128.GO30522@ZenIV.linux.org.uk> From: Miklos Szeredi Date: Mon, 11 Jun 2018 10:08:30 +0200 Message-ID: Subject: Re: [PATCH 23/39] ovl: add O_DIRECT support To: Al Viro Cc: Miklos Szeredi , overlayfs , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Sun, Jun 10, 2018 at 7:31 AM, Al Viro wrote: > On Tue, May 29, 2018 at 04:43:23PM +0200, Miklos Szeredi wrote: >> Signed-off-by: Miklos Szeredi >> --- >> fs/overlayfs/file.c | 3 +++ >> 1 file changed, 3 insertions(+) >> >> diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c >> index 3f610a5b38e4..e5e7ccaaf9ec 100644 >> --- a/fs/overlayfs/file.c >> +++ b/fs/overlayfs/file.c >> @@ -110,6 +110,9 @@ static int ovl_open(struct inode *inode, struct file *file) >> if (IS_ERR(realfile)) >> return PTR_ERR(realfile); >> >> + /* For O_DIRECT dentry_open() checks f_mapping->a_ops->direct_IO */ >> + file->f_mapping = realfile->f_mapping; > > Umm... What happens if upper layer doesn't allow O_DIRECT, while the lower one does? Will get EINVAL on read(2) after copy up. Not sure if it can be called a regression, since it's a corner case of a corner case. I think proper solution is to support O_DIRECT unconditionally on upper (and for the likes of shmfs, just fall back to "cached" I/O). Thanks, Miklos