Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit a78d9f0d authored by Miklos Szeredi's avatar Miklos Szeredi
Browse files

ovl: support multiple lower layers 



Allow "lowerdir=" option to contain multiple lower directories separated by
a colon (e.g. "lowerdir=/bin:/usr/bin").  Colon characters in filenames can
be escaped with a backslash.

Signed-off-by: default avatarMiklos Szeredi <mszeredi@suse.cz>
parent 53a08cb9

Documentation/filesystems/overlayfs.txt

+12 −0
Original line number Diff line number Diff line
@@ -159,6 +159,18 @@ overlay filesystem (though an operation on the name of the file such as 
rename or unlink will of course be noticed and handled).





Multiple lower layers

---------------------



Multiple lower layers can now be given using the the colon (":") as a

separator character between the directory names.  For example:



  mount -t overlay overlay -olowerdir=/lower1:/lower2:/lower3 /merged



As the example shows, "upperdir=" and "workdir=" may be omitted.  In that case

the overlay will be read-only.





Non-standard behavior

---------------------

fs/overlayfs/super.c

+83 −27
Original line number Diff line number Diff line
@@ -60,6 +60,8 @@ struct ovl_entry { 
	struct path lowerstack[];

};



#define OVL_MAX_STACK 500



const char *ovl_opaque_xattr = "trusted.overlay.opaque";



static struct dentry *__ovl_dentry_lower(struct ovl_entry *oe)
@@ -692,8 +694,12 @@ static bool ovl_is_allowed_fs_type(struct dentry *root) 


static int ovl_mount_dir_noesc(const char *name, struct path *path)

{

	int err;

	int err = -EINVAL;



	if (!*name) {

		pr_err("overlayfs: empty lowerdir\n");

		goto out;

	}

	err = kern_path(name, LOOKUP_FOLLOW, path);

	if (err) {

		pr_err("overlayfs: failed to resolve '%s': %i\n", name, err);
@@ -735,7 +741,7 @@ static int ovl_lower_dir(const char *name, struct path *path, long *namelen, 
	int err;

	struct kstatfs statfs;



	err = ovl_mount_dir(name, path);

	err = ovl_mount_dir_noesc(name, path);

	if (err)

		goto out;
@@ -767,15 +773,38 @@ static bool ovl_workdir_ok(struct dentry *workdir, struct dentry *upperdir) 
	return ok;

}



static unsigned int ovl_split_lowerdirs(char *str)

{

	unsigned int ctr = 1;

	char *s, *d;



	for (s = d = str;; s++, d++) {

		if (*s == '\\') {

			s++;

		} else if (*s == ':') {

			*d = '\0';

			ctr++;

			continue;

		}

		*d = *s;

		if (!*s)

			break;

	}

	return ctr;

}



static int ovl_fill_super(struct super_block *sb, void *data, int silent)

{

	struct path lowerpath;

	struct path upperpath = { NULL, NULL };

	struct path workpath = { NULL, NULL };

	struct dentry *root_dentry;

	struct ovl_entry *oe;

	struct ovl_fs *ufs;

	struct vfsmount *mnt;

	struct path *stack = NULL;

	char *lowertmp;

	char *lower;

	unsigned int numlower;

	unsigned int stacklen = 0;

	unsigned int i;

	int err;
@@ -820,11 +849,29 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent) 
		}

		sb->s_stack_depth = upperpath.mnt->mnt_sb->s_stack_depth;

	}

	err = -ENOMEM;

	lowertmp = kstrdup(ufs->config.lowerdir, GFP_KERNEL);

	if (!lowertmp)

		goto out_put_workpath;



	err = -EINVAL;

	stacklen = ovl_split_lowerdirs(lowertmp);

	if (stacklen > OVL_MAX_STACK)

		goto out_free_lowertmp;



	stack = kcalloc(stacklen, sizeof(struct path), GFP_KERNEL);

	if (!stack)

		goto out_free_lowertmp;



	err = ovl_lower_dir(ufs->config.lowerdir, &lowerpath,

	lower = lowertmp;

	for (numlower = 0; numlower < stacklen; numlower++) {

		err = ovl_lower_dir(lower, &stack[numlower],

				    &ufs->lower_namelen, &sb->s_stack_depth);

		if (err)

		goto out_put_workpath;

			goto out_put_lowerpath;



		lower = strchr(lower, '\0') + 1;

	}



	err = -EINVAL;

	sb->s_stack_depth++;
@@ -850,12 +897,12 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent) 
		}

	}



	ufs->lower_mnt = kcalloc(1, sizeof(struct vfsmount *), GFP_KERNEL);

	ufs->lower_mnt = kcalloc(numlower, sizeof(struct vfsmount *), GFP_KERNEL);

	if (ufs->lower_mnt == NULL)

		goto out_put_workdir;

	for (i = 0; i < numlower; i++) {

		struct vfsmount *mnt = clone_private_mount(&stack[i]);



	mnt = clone_private_mount(&lowerpath);

	err = PTR_ERR(mnt);

		if (IS_ERR(mnt)) {

			pr_err("overlayfs: failed to clone lowerpath\n");

			goto out_put_lower_mnt;
@@ -866,8 +913,9 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent) 
		 */

		mnt->mnt_flags |= MNT_READONLY;



	ufs->lower_mnt[0] = mnt;

	ufs->numlower = 1;

		ufs->lower_mnt[ufs->numlower] = mnt;

		ufs->numlower++;

	}



	/* If the upper fs is r/o or nonexistent, we mark overlayfs r/o too */

	if (!ufs->upper_mnt || (ufs->upper_mnt->mnt_sb->s_flags & MS_RDONLY))
@@ -876,7 +924,7 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent) 
	sb->s_d_op = &ovl_dentry_operations;



	err = -ENOMEM;

	oe = ovl_alloc_entry(1);

	oe = ovl_alloc_entry(numlower);

	if (!oe)

		goto out_put_lower_mnt;
@@ -885,12 +933,16 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent) 
		goto out_free_oe;



	mntput(upperpath.mnt);

	mntput(lowerpath.mnt);

	for (i = 0; i < numlower; i++)

		mntput(stack[i].mnt);

	path_put(&workpath);

	kfree(lowertmp);



	oe->__upperdentry = upperpath.dentry;

	oe->lowerstack[0].dentry = lowerpath.dentry;

	oe->lowerstack[0].mnt = ufs->lower_mnt[0];

	for (i = 0; i < numlower; i++) {

		oe->lowerstack[i].dentry = stack[i].dentry;

		oe->lowerstack[i].mnt = ufs->lower_mnt[i];

	}



	root_dentry->d_fsdata = oe;
@@ -912,7 +964,11 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent) 
out_put_upper_mnt:

	mntput(ufs->upper_mnt);

out_put_lowerpath:

	path_put(&lowerpath);

	for (i = 0; i < numlower; i++)

		path_put(&stack[i]);

	kfree(stack);

out_free_lowertmp:

	kfree(lowertmp);

out_put_workpath:

	path_put(&workpath);

out_put_upperpath: