On Mon, Jan 06, 2020 at 08:58:23PM +0100, Miklos Szeredi wrote:
> On Mon, Jan 6, 2020 at 7:35 PM Vivek Goyal <vgoyal@xxxxxxxxxx> wrote:
> >
> > On Mon, Jan 06, 2020 at 05:27:05PM +0000, Ernst, Eric wrote:
> >
> > [CC linux-unionfs@xxxxxxxxxxxxxxx and amir]
> >
> > > Hi Miklos,
> > >
> > > One of the popular use cases for Kata Containers is running docker-in-docker. That is, a container image is run which in turn will make use of a container runtime to do a container build.
> > >
> > > When combined with virtio-fs, we end up with a configuration like:
> > > xfs/ext4 -> overlayfs -> virtio-fs -> overlayfs
> > >
> > > As discussed in [1], per overlayfs spec:
> > > "The upper filesystem will normally be writable and if it is it must support the creation of trusted.* extended attributes, and must provide valid d_type in readdir responses, so NFS is not suitable."
> > >
> >
> > I don't know exaactly the reasons why NFS is not supported as upper. Are
> > above only two reasons? These might work with virtio-fs depending on
> > underlying filesystem. If yes, should we check for these properties
> > at mount time (instead of relying on dentry flags only,
> > ovl_dentry_remote()).
> >
> > I feel there is more to it.
>
> NFS also has these automount points, that we currently can't cope with
> in overlayfs. And there's revalidation, which we reject on upper
> simply because overlayfs currently doesn't call ->revalidate() on
> upper. Not that we would not be able to, it's just something that
> probably needs some thought.
>
> Virtio-fs does not yet have the magic automount thing (which would be
> useful to resolve inode number conflicts), but it does have
> revalidate. In the virtio-fs case, not calling ->revalidate() should
> not be a problem, so it's safe to try out this configuration by adding
> a hack to disable the remote check in case of a virtio-fs upper.
Here is a hack patch to provide an exception to allow virtiofs as upper
filesystem for overlayfs.
I can mount now but I get warning that upper does not support xattr, hence
disabling index and metaocopy. Still need to test why that's the case. I
thought xattr are supported on virtiofs.
Subject: overlayfs: Allow virtiofs as overlayfs upper
This is a hack patch to allow virtiofs as overlayfs upper filesystem. At
this point of time it is meant for testing and see what issues crop up.
Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx>
---
fs/overlayfs/namei.c | 3 ++-
fs/overlayfs/overlayfs.h | 2 ++
fs/overlayfs/super.c | 4 ++--
fs/overlayfs/util.c | 24 ++++++++++++++++++++++--
4 files changed, 28 insertions(+), 5 deletions(-)
Index: rhvgoyal-linux/fs/overlayfs/util.c
===================================================================
--- rhvgoyal-linux.orig/fs/overlayfs/util.c 2020-01-07 11:03:22.584732137 -0500
+++ rhvgoyal-linux/fs/overlayfs/util.c 2020-01-07 11:03:55.424732137 -0500
@@ -102,11 +102,31 @@ struct ovl_entry *ovl_alloc_entry(unsign
return oe;
}
+bool ovl_dentry_union(struct dentry *dentry)
+{
+ return dentry->d_flags & DCACHE_OP_REAL;
+}
+
bool ovl_dentry_remote(struct dentry *dentry)
{
return dentry->d_flags &
- (DCACHE_OP_REVALIDATE | DCACHE_OP_WEAK_REVALIDATE
- DCACHE_OP_REAL);
+ (DCACHE_OP_REVALIDATE | DCACHE_OP_WEAK_REVALIDATE);
+}
+
+bool ovl_dentry_valid_upper(struct dentry *dentry)
+{
+ struct file_system_type *fs_type;
+
+ if (ovl_dentry_union(dentry))
+ return false;
+
+ fs_type = dentry->d_sb->s_type;
+
+ /* Provide an exception for virtiofs */
+ if (ovl_dentry_remote(dentry) && strcmp(fs_type->name, "virtiofs"))
+ return false;
+
+ return true;
}
bool ovl_dentry_weird(struct dentry *dentry)
Index: rhvgoyal-linux/fs/overlayfs/super.c
===================================================================
--- rhvgoyal-linux.orig/fs/overlayfs/super.c 2020-01-07 11:03:22.584732137 -0500
+++ rhvgoyal-linux/fs/overlayfs/super.c 2020-01-07 11:03:55.427732137 -0500
@@ -751,7 +751,7 @@ static int ovl_mount_dir(const char *nam
err = ovl_mount_dir_noesc(tmp, path);
if (!err)
- if (ovl_dentry_remote(path->dentry)) {
+ if (!ovl_dentry_valid_upper(path->dentry)) {
pr_err("overlayfs: filesystem on '%s' not supported as upperdir\n",
tmp);
path_put_init(path);
@@ -792,7 +792,7 @@ static int ovl_lower_dir(const char *nam
*stack_depth = max(*stack_depth, path->mnt->mnt_sb->s_stack_depth);
- if (ovl_dentry_remote(path->dentry))
+ if (ovl_dentry_remote(path->dentry) || ovl_dentry_union(path->dentry))
*remote = true;
/*
Index: rhvgoyal-linux/fs/overlayfs/overlayfs.h
===================================================================
--- rhvgoyal-linux.orig/fs/overlayfs/overlayfs.h 2020-01-07 11:03:22.584732137 -0500
+++ rhvgoyal-linux/fs/overlayfs/overlayfs.h 2020-01-07 11:03:55.426732137 -0500
@@ -228,6 +228,8 @@ bool ovl_index_all(struct super_block *s
bool ovl_verify_lower(struct super_block *sb);
struct ovl_entry *ovl_alloc_entry(unsigned int numlower);
bool ovl_dentry_remote(struct dentry *dentry);
+bool ovl_dentry_union(struct dentry *dentry);
+bool ovl_dentry_valid_upper(struct dentry *dentry);
bool ovl_dentry_weird(struct dentry *dentry);
enum ovl_path_type ovl_path_type(struct dentry *dentry);
void ovl_path_upper(struct dentry *dentry, struct path *path);
Index: rhvgoyal-linux/fs/overlayfs/namei.c
===================================================================
--- rhvgoyal-linux.orig/fs/overlayfs/namei.c 2020-01-07 11:03:22.584732137 -0500
+++ rhvgoyal-linux/fs/overlayfs/namei.c 2020-01-07 11:03:55.428732137 -0500
@@ -845,7 +845,8 @@ struct dentry *ovl_lookup(struct inode *
if (err)
goto out;
- if (upperdentry && unlikely(ovl_dentry_remote(upperdentry))) {
+ if (upperdentry &&
+ unlikely(!ovl_dentry_valid_upper(upperdentry))) {
dput(upperdentry);
err = -EREMOTE;
goto out;
