ovl: introduce the inodes index dir feature

Create the index dir on mount. The index dir will contain hardlinks to
upper inodes, named after the hex representation of their origin lower
inodes.

The index dir is going to be used to prevent breaking lower hardlinks
on copy up and to implement overlayfs NFS export.

Because the feature is not fully backward compat, enabling the feature
is opt-in by config/module/mount option.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

1 files changed, 64 insertions, 2 deletions

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index fea7bd496f2e..fa83b3245124 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -34,6 +34,11 @@ module_param_named(redirect_dir, ovl_redirect_dir_def, bool, 0644);
 MODULE_PARM_DESC(ovl_redirect_dir_def,
 		 "Default to on or off for the redirect_dir feature");
 
+static bool ovl_index_def = IS_ENABLED(CONFIG_OVERLAY_FS_INDEX);
+module_param_named(index, ovl_index_def, bool, 0644);
+MODULE_PARM_DESC(ovl_index_def,
+		 "Default to on or off for the inodes index feature");
+
 static void ovl_dentry_release(struct dentry *dentry)
 {
 	struct ovl_entry *oe = dentry->d_fsdata;
@@ -203,6 +208,7 @@ static void ovl_put_super(struct super_block *sb)
 	struct ovl_fs *ufs = sb->s_fs_info;
 	unsigned i;
 
+	dput(ufs->indexdir);
 	dput(ufs->workdir);
 	ovl_inuse_unlock(ufs->workbasedir);
 	dput(ufs->workbasedir);
@@ -265,6 +271,12 @@ static int ovl_statfs(struct dentry *dentry, struct kstatfs *buf)
 	return err;
 }
 
+/* Will this overlay be forced to mount/remount ro? */
+static bool ovl_force_readonly(struct ovl_fs *ufs)
+{
+	return (!ufs->upper_mnt || !ufs->workdir);
+}
+
 /**
  * ovl_show_options
  *
@@ -286,6 +298,9 @@ static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
 	if (ufs->config.redirect_dir != ovl_redirect_dir_def)
 		seq_printf(m, ",redirect_dir=%s",
 			   ufs->config.redirect_dir ? "on" : "off");
+	if (ufs->config.index != ovl_index_def)
+		seq_printf(m, ",index=%s",
+			   ufs->config.index ? "on" : "off");
 	return 0;
 }
 
@@ -293,7 +308,7 @@ static int ovl_remount(struct super_block *sb, int *flags, char *data)
 {
 	struct ovl_fs *ufs = sb->s_fs_info;
 
-	if (!(*flags & MS_RDONLY) && (!ufs->upper_mnt || !ufs->workdir))
+	if (!(*flags & MS_RDONLY) && ovl_force_readonly(ufs))
 		return -EROFS;
 
 	return 0;
@@ -317,6 +332,8 @@ enum {
 	OPT_DEFAULT_PERMISSIONS,
 	OPT_REDIRECT_DIR_ON,
 	OPT_REDIRECT_DIR_OFF,
+	OPT_INDEX_ON,
+	OPT_INDEX_OFF,
 	OPT_ERR,
 };
 
@@ -327,6 +344,8 @@ static const match_table_t ovl_tokens = {
 	{OPT_DEFAULT_PERMISSIONS,	"default_permissions"},
 	{OPT_REDIRECT_DIR_ON,		"redirect_dir=on"},
 	{OPT_REDIRECT_DIR_OFF,		"redirect_dir=off"},
+	{OPT_INDEX_ON,			"index=on"},
+	{OPT_INDEX_OFF,			"index=off"},
 	{OPT_ERR,			NULL}
 };
 
@@ -399,6 +418,14 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config)
 			config->redirect_dir = false;
 			break;
 
+		case OPT_INDEX_ON:
+			config->index = true;
+			break;
+
+		case OPT_INDEX_OFF:
+			config->index = false;
+			break;
+
 		default:
 			pr_err("overlayfs: unrecognized mount option \"%s\" or missing value\n", p);
 			return -EINVAL;
@@ -417,6 +444,7 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config)
 }
 
 #define OVL_WORKDIR_NAME "work"
+#define OVL_INDEXDIR_NAME "index"
 
 static struct dentry *ovl_workdir_create(struct super_block *sb,
 					 struct ovl_fs *ufs,
@@ -610,6 +638,15 @@ static int ovl_lower_dir(const char *name, struct path *path,
 	if (ovl_dentry_remote(path->dentry))
 		*remote = true;
 
+	/*
+	 * The inodes index feature needs to encode and decode file
+	 * handles, so it requires that all layers support them.
+	 */
+	if (ofs->config.index && !ovl_can_decode_fh(path->dentry->d_sb)) {
+		ofs->config.index = false;
+		pr_warn("overlayfs: fs on '%s' does not support file handles, falling back to index=off.\n", name);
+	}
+
 	return 0;
 
 out_put:
@@ -807,6 +844,7 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 		goto out;
 
 	ufs->config.redirect_dir = ovl_redirect_dir_def;
+	ufs->config.index = ovl_index_def;
 	err = ovl_parse_opt((char *) data, &ufs->config);
 	if (err)
 		goto out_free_config;
@@ -965,6 +1003,13 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 			} else {
 				vfs_removexattr(ufs->workdir, OVL_XATTR_OPAQUE);
 			}
+
+			/* Check if upper/work fs supports file handles */
+			if (ufs->config.index &&
+			    !ovl_can_decode_fh(ufs->workdir->d_sb)) {
+				ufs->config.index = false;
+				pr_warn("overlayfs: upper fs does not support file handles, falling back to index=off.\n");
+			}
 		}
 	}
 
@@ -1002,6 +1047,21 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 	else if (ufs->upper_mnt->mnt_sb != ufs->same_sb)
 		ufs->same_sb = NULL;
 
+	if (!(ovl_force_readonly(ufs)) && ufs->config.index) {
+		ufs->indexdir = ovl_workdir_create(sb, ufs, workpath.dentry,
+						   OVL_INDEXDIR_NAME, true);
+		err = PTR_ERR(ufs->indexdir);
+		if (IS_ERR(ufs->indexdir))
+			goto out_put_lower_mnt;
+
+		if (!ufs->indexdir)
+			pr_warn("overlayfs: try deleting index dir or mounting with '-o index=off' to disable inodes index.\n");
+	}
+
+	/* Show index=off/on in /proc/mounts for any of the reasons above */
+	if (!ufs->indexdir)
+		ufs->config.index = false;
+
 	if (remote)
 		sb->s_d_op = &ovl_reval_dentry_operations;
 	else
@@ -1009,7 +1069,7 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 
 	ufs->creator_cred = cred = prepare_creds();
 	if (!cred)
-		goto out_put_lower_mnt;
+		goto out_put_indexdir;
 
 	/* Never override disk quota limits or use reserved space */
 	cap_lower(cred->cap_effective, CAP_SYS_RESOURCE);
@@ -1058,6 +1118,8 @@ out_free_oe:
 	kfree(oe);
 out_put_cred:
 	put_cred(ufs->creator_cred);
+out_put_indexdir:
+	dput(ufs->indexdir);
 out_put_lower_mnt:
 	for (i = 0; i < ufs->numlower; i++)
 		mntput(ufs->lower_mnt[i]);