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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
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+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
---------------------

+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: