Re: failed open: No data available

From: Michael Labriola <michael.d.labriola@gmail.com>
To: Amir Goldstein <amir73il@gmail.com>
Cc: overlayfs <linux-unionfs@vger.kernel.org>,
	Miklos Szeredi <miklos@szeredi.hu>
Subject: Re: failed open: No data available
Date: Thu, 17 Dec 2020 14:46:38 -0500	[thread overview]
Message-ID: <CAOQxz3y8N6ny23iA1Fe0L4M1gR=FHP5xANZXquu4NSLoucorKw@mail.gmail.com> (raw)
In-Reply-To: <CAOQ4uxjmUY+N6sBoD-d2MN4eehPCcWzBXTHkDqAcCVtkpbG2kw@mail.gmail.com>

On Thu, Dec 17, 2020 at 1:07 PM Amir Goldstein <amir73il@gmail.com> wrote:
>
> On Thu, Dec 17, 2020 at 6:22 PM Michael Labriola
*snip*
> > On Thu, Dec 17, 2020 at 7:00 AM Amir Goldstein <amir73il@gmail.com> wrote:
> > Thanks, Amir.  I didn't have CONFIG_DYNAMIC_DEBUG enabled, so
>
> I honestly don't expect to find much in the existing overlay debug prints
> but you never know..
> I suspect you will have to add debug prints to find the problem.

Ok, here goes.  I had to setup a new virtual machine that doesn't use
overlayfs for its root filesystem because turning on dynamic debug
gave way too much output for a nice controlled test.  It's exhibiting
the same behavior as my previous tests (5.8 good, 5.9 bad).  The is
with a freshly compiled 5.9.15 w/ CONFIG_OVERLAY_FS_XINO_AUTO turned
off and CONFIG_DYNAMIC_DEBUG turned on.  Here's what we get:

 echo "file fs/overlayfs/*  +p" > /sys/kernel/debug/dynamic_debug/control
 mount borky2.sqsh t
 mount -t tmpfs tmp tt
 mkdir -p tt/upper/{upper,work}
 mount -t overlay -o \
    lowerdir=t,upperdir=tt/upper/upper,workdir=tt/upper/work blarg ttt
[  164.505193] overlayfs: mkdir(work/work, 040000) = 0
[  164.505204] overlayfs: tmpfile(work/work, 0100000) = 0
[  164.505209] overlayfs: create(work/#3, 0100000) = 0
[  164.505210] overlayfs: rename(work/#3, work/#4, 0x4)
[  164.505216] overlayfs: unlink(work/#3) = 0
[  164.505217] overlayfs: unlink(work/#4) = 0
[  164.505221] overlayfs: setxattr(work/work,
"trusted.overlay.opaque", "0", 1, 0x0) = 0

 touch ttt/FOO
touch: cannot touch 'ttt/FOO': No data available
[  191.919498] overlayfs: setxattr(upper/upper,
"trusted.overlay.impure", "y", 1, 0x0) = 0
[  191.919523] overlayfs: tmpfile(work/work, 0100644) = 0
[  191.919788] overlayfs: tmpfile(work/work, 0100644) = 0

That give you any hints?  I'll start reading through the overlayfs
code.  I've never actually looked at it, so I'll be planting printk
calls at random.  ;-)

-- 
Michael D Labriola
21 Rip Van Winkle Cir
Warwick, RI 02886
401-316-9844 (cell)