On 2025-05-06 19:16:04 +0100, Al Viro wrote:
> On Tue, May 06, 2025 at 07:54:32PM +0200, Klara Modin wrote:
>
> > > > Though now I hit another issue which I don't know if it's related or
> > > > not. I'm using an overlay mount with squashfs as lower and btrfs as
> > > > upper. The mount fails with invalid argument and I see this in the log:
> > > >
> > > > overlayfs: failed to clone upperpath
> > >
> > > Seeing that you already have a kernel with that thing reverted, could
> > > you check if the problem exists there?
> >
> > Yeah, it works fine with the revert instead.
>
> Interesting... That message means that you've got clone_private_mount()
> returning an error; the thing is, mount passed to it has come from
> pathname lookup - it is *not* the mount created by that fc_mount() of
> vfs_create_mount() in the modified code. That one gets passed to
> mount_subvol() and consumed there (by mount_subtree()). All that is returned
> is root dentry; the mount passed to clone_private_mount() is created
> from scratch using dentry left by btrfs_get_tree_subvol() in its fc->root -
> see
> dentry = mount_subvol(ctx->subvol_name, ctx->subvol_objectid, mnt);
> ctx->subvol_name = NULL;
> if (IS_ERR(dentry))
> return PTR_ERR(dentry);
>
> fc->root = dentry;
> return 0;
> in the end of btrfs_get_tree_subvol().
>
> What's more, on the overlayfs side we managed to get to
> upper_mnt = clone_private_mount(upperpath);
> err = PTR_ERR(upper_mnt);
> if (IS_ERR(upper_mnt)) {
> pr_err("failed to clone upperpath\n");
> goto out;
> so the upper path had been resolved...
>
> OK, let's try to see what clone_private_mount() is unhappy about...
> Could you try the following on top of -next + braino fix and see
> what shows up? Another interesting thing, assuming you can get
> to shell after overlayfs mount failure, would be /proc/self/mountinfo
> contents and stat(1) output for upper path of your overlayfs mount...
It looks like the mount never succeded in the first place? It doesn't
appear in /proc/self/mountinfo at all:
2 2 0:2 / / rw - rootfs rootfs rw
24 2 0:22 / /proc rw,relatime - proc proc rw
25 2 0:23 / /sys rw,relatime - sysfs sys rw
26 2 0:6 / /dev rw,relatime - devtmpfs dev rw,size=481992k,nr_inodes=120498,mode=755
27 2 259:1 / /mnt/root-ro ro,relatime - squashfs /dev/nvme0n1 ro,errors=continue
I get the "kern_mount?" message.
