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@redhat.com> wrote:
On Mon, Jan 06, 2020 at 05:27:05PM +0000, Ernst, Eric wrote:
[CC linux-unionfs@vger.kernel.org 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@redhat.com> --- 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;