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From: Amir Goldstein <amir73il@gmail.com>
To: Sargun Dhillon <sargun@sargun.me>
Cc: Vivek Goyal <vgoyal@redhat.com>,
	overlayfs <linux-unionfs@vger.kernel.org>,
	Miklos Szeredi <miklos@szeredi.hu>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Giuseppe Scrivano <gscrivan@redhat.com>,
	Daniel J Walsh <dwalsh@redhat.com>,
	David Howells <dhowells@redhat.com>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Chengguang Xu <cgxu519@mykernel.net>
Subject: Re: [RFC PATCH 3/3] overlay: Add the ability to remount volatile directories when safe
Date: Tue, 17 Nov 2020 07:41:39 +0200	[thread overview]
Message-ID: <CAOQ4uxijv8JiJzZ+Sxt8iXfZVbZvDNzK1PJRLexMAHnVdJEg=g@mail.gmail.com> (raw)
In-Reply-To: <20201116221401.GA21744@ircssh-2.c.rugged-nimbus-611.internal>

> > > I think upper files data can "evaporate" even as the overlay is still mounted.
> >
> > I think assumption of volatile containers was that data will remain
> > valid as long as machine does not crash/shutdown. We missed the case
> > of possibility of writeback errors during those discussions.
> >
> > And if data can evaporate without anyway to know that somehthing
> > is gone wrong, I don't know how that's useful for applications.
> >
> > Also, first we need to fix the case of writeback error handling
> > for volatile containers while it is mounted before one tries to fix it
> > for writeback error detection during remount, IMHO.
> >
> > Thanks
> > Vivek
> >
>
> I feel like this is an infamous Linux problem, and lots[1][2][3][4] has been said
> on the topic, and there's not really a general purpose solution to it. I think that
> most filesystems offer a choice of "continue" or "fail-stop" (readonly), and if
> the upperdir lives on that filesystem, we will get the feedback from it.
>
> I can respin my patch with just the "boot id" and superblock ID check if folks
> are fine with that, and we can figure out how to resolve the writeback issues
> later.
>

On the contrary. Your code for error check is very valuable and more
important than the remount feature.

If you change ovl_should_sync() to check for error since mount and
return error in that case, which all callers will check, then I think you
fix the evaporating files issue and that needs to come first with
stable kernel backport IMO.

Thanks,
Amir.

  reply	other threads:[~2020-11-17  5:42 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-16  4:57 [RFC PATCH 0/3] Make overlayfs volatile mounts reusable Sargun Dhillon
2020-11-16  4:57 ` [RFC PATCH 1/3] fs: Add s_instance_id field to superblock for unique identification Sargun Dhillon
2020-11-16  5:07   ` Sargun Dhillon
2020-11-16  4:57 ` [RFC PATCH 2/3] overlay: Add ovl_do_getxattr helper Sargun Dhillon
2020-11-16 11:00   ` Amir Goldstein
2020-11-16  4:57 ` [RFC PATCH 3/3] overlay: Add the ability to remount volatile directories when safe Sargun Dhillon
2020-11-16  9:31   ` Amir Goldstein
2020-11-16 10:30     ` Sargun Dhillon
2020-11-16 11:17       ` Amir Goldstein
2020-11-16 12:52         ` Amir Goldstein
2020-11-16 14:42   ` Vivek Goyal
2020-11-16 14:45     ` Vivek Goyal
2020-11-16 15:20     ` Amir Goldstein
2020-11-16 16:36       ` Vivek Goyal
2020-11-16 18:25         ` Sargun Dhillon
2020-11-16 19:27           ` Vivek Goyal
2020-11-16 20:18         ` Amir Goldstein
2020-11-16 21:09           ` Vivek Goyal
2020-11-17  5:33             ` Amir Goldstein
2020-11-17 14:48               ` Vivek Goyal
2020-11-17 15:24                 ` Amir Goldstein
2020-11-17 15:40                   ` Vivek Goyal
2020-11-17 16:46                   ` Vivek Goyal
2020-11-17 18:03                     ` Amir Goldstein
2020-11-17 18:29                       ` Vivek Goyal
2020-11-18  7:24                         ` Amir Goldstein
2020-11-18  8:27                           ` Sargun Dhillon
2020-11-18 10:46                             ` Amir Goldstein
2020-11-18 14:55                           ` Vivek Goyal
2020-11-16 21:26           ` Vivek Goyal
2020-11-16 22:14             ` Sargun Dhillon
2020-11-17  5:41               ` Amir Goldstein [this message]
2020-11-17 17:05               ` Vivek Goyal
2020-11-16 17:38     ` Sargun Dhillon

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