Re: linux / overlay / OpenWrt / problems with full working dir

Re: linux / overlay / OpenWrt / problems with full working dir

[Miklos Szeredi]

[linux-unionfs added to Cc]

On Tue, May 19, 2015 at 09:51:20AM +0200, Bastian Bittorf wrote:
> Hi Miklos,
> 
> sorry for writing directly to you, feel free to forward
> this to the appropriate mailinglist.
> 
> we have a problem with mainline overlay filesystem on kernel 3.18:
> https://dev.openwrt.org/ticket/19564
> 
> 2 things are odd:
> when the working filesystem is full, overlays fails with:
> 
> overlayfs: failed to create directory /overlay/work/work
> 
> what is strange, that we call it with:
> 
> mount(overlay, "/mnt", "overlay", MS_NOATIME, lowerdir)
> 
> see here:
> http://nbd.name/gitweb.cgi?p=fstools.git;a=blob;f=libfstools/mount.c;h=81176ce399b4cd8e2d347c0008c13dec92407f55;hb=e6004000ff15d7bd32cf5663e8690fc94d7ec747#l125
> 
> do you have an idea whats wrong?
> 1) is it really needed, that we need space for creating dir "/overlay/work"?
> 2) why does overlay need "/overlay/work/work"?

The work directory is needed for atomic copy-up and similar.  It is not actually
necessary to mount a read-only overlay.  Post 4.0 it is possible to mount the
overlay without workdir (but even then it won't happen automatically in case the
upper fs is full, so this should be fixed in the latest kernel too).

Could you please try the following patch?  If the workdir can't be created it
will fall back to mounting the overlay read-only.

Thanks,
Miklos

---
 fs/overlayfs/copy_up.c |    3 +++
 fs/overlayfs/dir.c     |    9 +++++++++
 fs/overlayfs/super.c   |   12 +++++++++---
 3 files changed, 21 insertions(+), 3 deletions(-)

--- a/fs/overlayfs/copy_up.c
+++ b/fs/overlayfs/copy_up.c
@@ -300,6 +300,9 @@ int ovl_copy_up_one(struct dentry *paren
 	struct cred *override_cred;
 	char *link = NULL;
 
+	if (WARN_ON(!workdir))
+		return -EROFS;
+
 	ovl_path_upper(parent, &parentpath);
 	upperdir = parentpath.dentry;
 
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -222,6 +222,9 @@ static struct dentry *ovl_clear_empty(st
 	struct kstat stat;
 	int err;
 
+	if (WARN_ON(!workdir))
+		return ERR_PTR(-EROFS);
+
 	err = ovl_lock_rename_workdir(workdir, upperdir);
 	if (err)
 		goto out;
@@ -322,6 +325,9 @@ static int ovl_create_over_whiteout(stru
 	struct dentry *newdentry;
 	int err;
 
+	if (WARN_ON(!workdir))
+		return -EROFS;
+
 	err = ovl_lock_rename_workdir(workdir, upperdir);
 	if (err)
 		goto out;
@@ -506,6 +512,9 @@ static int ovl_remove_and_whiteout(struc
 	struct dentry *opaquedir = NULL;
 	int err;
 
+	if (WARN_ON(!workdir))
+		return -EROFS;
+
 	if (is_dir) {
 		opaquedir = ovl_check_empty_and_clear(dentry);
 		err = PTR_ERR(opaquedir);
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -740,9 +740,15 @@ static int ovl_fill_super(struct super_b
 	ufs->workdir = ovl_workdir_create(ufs->upper_mnt, workpath.dentry);
 	err = PTR_ERR(ufs->workdir);
 	if (IS_ERR(ufs->workdir)) {
-		pr_err("overlayfs: failed to create directory %s/%s\n",
-		       ufs->config.workdir, OVL_WORKDIR_NAME);
-		goto out_put_lower_mnt;
+		if (err == -ENOSPC || err == -EROFS) {
+			pr_warning("overlayfs: failed to work directory (%s), mounting read-only\n", err == ENOSPC ? "ENOSPC" : "EROFS");
+			sb->s_flags |= MS_RDONLY;
+			ufs->workdir = NULL;
+		} else {
+			pr_err("overlayfs: failed to create directory %s/%s\n",
+			       ufs->config.workdir, OVL_WORKDIR_NAME);
+			goto out_put_lower_mnt;
+		}
 	}
 
 	/*

Re: linux / overlay / OpenWrt / problems with full working dir

[hujianyang]

Hi Miklos,

On 2015/5/19 17:03, Miklos Szeredi wrote:
> 
> ---
>  fs/overlayfs/copy_up.c |    3 +++
>  fs/overlayfs/dir.c     |    9 +++++++++
>  fs/overlayfs/super.c   |   12 +++++++++---
>  3 files changed, 21 insertions(+), 3 deletions(-)
> 
> --- a/fs/overlayfs/copy_up.c
> +++ b/fs/overlayfs/copy_up.c
> @@ -300,6 +300,9 @@ int ovl_copy_up_one(struct dentry *paren
>  	struct cred *override_cred;
>  	char *link = NULL;
>  
> +	if (WARN_ON(!workdir))
> +		return -EROFS;
> +

When will this condition occur?

>  	ovl_path_upper(parent, &parentpath);
>  	upperdir = parentpath.dentry;
>  
> --- a/fs/overlayfs/dir.c
> +++ b/fs/overlayfs/dir.c
> @@ -222,6 +222,9 @@ static struct dentry *ovl_clear_empty(st
>  	struct kstat stat;
>  	int err;
>  
> +	if (WARN_ON(!workdir))
> +		return ERR_PTR(-EROFS);
> +
>  	err = ovl_lock_rename_workdir(workdir, upperdir);
>  	if (err)
>  		goto out;
> @@ -322,6 +325,9 @@ static int ovl_create_over_whiteout(stru
>  	struct dentry *newdentry;
>  	int err;
>  
> +	if (WARN_ON(!workdir))
> +		return -EROFS;
> +
>  	err = ovl_lock_rename_workdir(workdir, upperdir);
>  	if (err)
>  		goto out;
> @@ -506,6 +512,9 @@ static int ovl_remove_and_whiteout(struc
>  	struct dentry *opaquedir = NULL;
>  	int err;
>  
> +	if (WARN_ON(!workdir))
> +		return -EROFS;
> +
>  	if (is_dir) {
>  		opaquedir = ovl_check_empty_and_clear(dentry);
>  		err = PTR_ERR(opaquedir);
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -740,9 +740,15 @@ static int ovl_fill_super(struct super_b
>  	ufs->workdir = ovl_workdir_create(ufs->upper_mnt, workpath.dentry);
>  	err = PTR_ERR(ufs->workdir);
>  	if (IS_ERR(ufs->workdir)) {
> -		pr_err("overlayfs: failed to create directory %s/%s\n",
> -		       ufs->config.workdir, OVL_WORKDIR_NAME);
> -		goto out_put_lower_mnt;
> +		if (err == -ENOSPC || err == -EROFS) {

Since upper fs should not be R/O after commit 71cbad7e694ee81,
could the return value here be -EROFS?

> +			pr_warning("overlayfs: failed to work directory (%s), mounting read-only\n", err == ENOSPC ? "ENOSPC" : "EROFS");
> +			sb->s_flags |= MS_RDONLY;
> +			ufs->workdir = NULL;
> +		} else {
> +			pr_err("overlayfs: failed to create directory %s/%s\n",
> +			       ufs->config.workdir, OVL_WORKDIR_NAME);
> +			goto out_put_lower_mnt;
> +		}
>  	}
>  
>  	/*
> --
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> 
> .
> 

Re: linux / overlay / OpenWrt / problems with full working dir

[Bastian Bittorf]

* Miklos Szeredi <miklos@szeredi.hu> [19.05.2015 11:19]:
> The work directory is needed for atomic copy-up and similar.  It is not actually
> necessary to mount a read-only overlay.  Post 4.0 it is possible to mount the
> overlay without workdir (but even then it won't happen automatically in case the
> upper fs is full, so this should be fixed in the latest kernel too).
> 
> Could you please try the following patch?  If the workdir can't be created it
> will fall back to mounting the overlay read-only.

Thank you!
I applied it on top of 3.18 and it works.
Here some output with full 'work-dir'/jffs2:

...
[    8.800000] jffs2: notice: (323) jffs2_build_xattr_subsystem: complete building xattr subsystem, 2 of xdatum (2 unc hecked, 0 orphan) and 2 of xref (0 dead, 0 orphan) found.
[    8.820000] mount_root: switching to jffs2 overlay
[    9.030000] overlayfs: failed to work directory (EROFS), mounting read-only
...
 
root@box:~ df -h
Filesystem                Size      Used Available Use% Mounted on
rootfs                  576.0K    532.0K     44.0K  92% /
/dev/root                 2.3M      2.3M         0 100% /rom
tmpfs                    14.0M      1.2M     12.8M   8% /tmp
/dev/mtdblock3          576.0K    532.0K     44.0K  92% /overlay
overlayfs:/overlay      576.0K    532.0K     44.0K  92% /
tmpfs                   512.0K         0    512.0K   0% /dev

root@box:~ mount
rootfs on / type rootfs (rw)
/dev/root on /rom type squashfs (ro,relatime)
proc on /proc type proc (rw,noatime)
sysfs on /sys type sysfs (rw,noatime)
tmpfs on /tmp type tmpfs (rw,nosuid,nodev,noatime)
/dev/mtdblock3 on /overlay type jffs2 (rw,noatime)
overlayfs:/overlay on / type overlay (ro,noatime,lowerdir=/,upperdir=/overlay/upper,workdir=/overlay/work)
tmpfs on /dev type tmpfs (rw,relatime,size=512k,mode=755)
devpts on /dev/pts type devpts (rw,relatime,mode=600)
debugfs on /sys/kernel/debug type debugfs (rw,noatime)

please apply it on your git, and we will cherrypick/backport it for OpenWrt.
(and close ticket https://dev.openwrt.org/ticket/19564)

bye, bastian

Re: linux / overlay / OpenWrt / problems with full working dir

[Miklos Szeredi]

On Tue, May 19, 2015 at 2:00 PM, Bastian Bittorf <bittorf@bluebottle.com> wrote:

> please apply it on your git, and we will cherrypick/backport it for OpenWrt.
> (and close ticket https://dev.openwrt.org/ticket/19564)

Pushed to:

  git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs.git
overlayfs-current

Thanks,
Miklos