ovl: add support for "nfs_export" configuration (f168f109) · Commits · 戴 / test

Documentation/filesystems/overlayfs.txt

+35 −0

Original line number	Diff line number	Diff line
		@@ -190,6 +190,24 @@ Mount options:
		Redirects are not created and not followed (equivalent to "redirect_dir=off"
		if "redirect_always_follow" feature is not enabled).

		When the NFS export feature is enabled, every copied up directory is
		indexed by the file handle of the lower inode and a file handle of the
		upper directory is stored in a "trusted.overlay.upper" extended attribute
		on the index entry. On lookup of a merged directory, if the upper
		directory does not match the file handle stores in the index, that is an
		indication that multiple upper directories may be redirected to the same
		lower directory. In that case, lookup returns an error and warns about
		a possible inconsistency.

		Because lower layer redirects cannot be verified with the index, enabling
		NFS export support on an overlay filesystem with no upper layer requires
		turning off redirect follow (e.g. "redirect_dir=nofollow").

		When the NFS export feature is enabled, all directory index entries are
		verified on mount time to check that upper file handles are not stale.
		This verification may cause significant overhead in some cases.


		Non-directories
		---------------

		@@ -299,6 +317,23 @@ filesystem are not allowed. If the underlying filesystem is changed,
		the behavior of the overlay is undefined, though it will not result in
		a crash or deadlock.

		When the overlay NFS export feature is enabled, overlay filesystems
		behavior on offline changes of the underlying lower layer is different
		than the behavior when NFS export is disabled.

		On every copy_up, an NFS file handle of the lower inode, along with the
		UUID of the lower filesystem, are encoded and stored in an extended
		attribute "trusted.overlay.origin" on the upper inode.

		When the NFS export feature is enabled, a lookup of a merged directory,
		that found a lower directory at the lookup path or at the path pointed
		to by the "trusted.overlay.redirect" extended attribute, will verify
		that the found lower directory file handle and lower filesystem UUID
		match the origin file handle that was stored at copy_up time. If a
		found lower directory does not match the stored origin, that directory
		will not be merged with the upper directory.


		Testsuite
		---------

fs/overlayfs/Kconfig

+22 −0

Original line number	Diff line number	Diff line
		@@ -50,3 +50,25 @@ config OVERLAY_FS_INDEX
		Note, that the inodes index feature is not backward compatible.
		That is, mounting an overlay which has an inodes index on a kernel
		that doesn't support this feature will have unexpected results.

		config OVERLAY_FS_NFS_EXPORT
		bool "Overlayfs: turn on NFS export feature by default"
		depends on OVERLAY_FS
		depends on OVERLAY_FS_INDEX
		help
		If this config option is enabled then overlay filesystems will use
		the inodes index dir to decode overlay NFS file handles by default.
		In this case, it is still possible to turn off NFS export support
		globally with the "nfs_export=off" module option or on a filesystem
		instance basis with the "nfs_export=off" mount option.

		The NFS export feature creates an index on copy up of every file and
		directory. This full index is used to detect overlay filesystems
		inconsistencies on lookup, like redirect from multiple upper dirs to
		the same lower dir. The full index may incur some overhead on mount
		time, especially when verifying that directory file handles are not
		stale.

		Note, that the NFS export feature is not backward compatible.
		That is, mounting an overlay which has a full index on a kernel
		that doesn't support this feature will have unexpected results.

fs/overlayfs/overlayfs.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -194,6 +194,8 @@ const struct cred ovl_override_creds(struct super_block sb);
		struct super_block ovl_same_sb(struct super_block sb);
		bool ovl_can_decode_fh(struct super_block *sb);
		struct dentry ovl_indexdir(struct super_block sb);
		bool ovl_index_all(struct super_block *sb);
		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_weird(struct dentry *dentry);

fs/overlayfs/ovl_entry.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -17,6 +17,7 @@ struct ovl_config {
		bool redirect_follow;
		const char *redirect_mode;
		bool index;
		bool nfs_export;
		};

		struct ovl_layer {

fs/overlayfs/super.c

+44 −5

Original line number	Diff line number	Diff line
		@@ -45,6 +45,11 @@ 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 bool ovl_nfs_export_def = IS_ENABLED(CONFIG_OVERLAY_FS_NFS_EXPORT);
		module_param_named(nfs_export, ovl_nfs_export_def, bool, 0644);
		MODULE_PARM_DESC(ovl_nfs_export_def,
		"Default to on or off for the NFS export feature");

		static void ovl_entry_stack_free(struct ovl_entry *oe)
		{
		unsigned int i;
		@@ -342,6 +347,9 @@ static int ovl_show_options(struct seq_file m, struct dentry dentry)
		seq_printf(m, ",redirect_dir=%s", ofs->config.redirect_mode);
		if (ofs->config.index != ovl_index_def)
		seq_printf(m, ",index=%s", ofs->config.index ? "on" : "off");
		if (ofs->config.nfs_export != ovl_nfs_export_def)
		seq_printf(m, ",nfs_export=%s", ofs->config.nfs_export ?
		"on" : "off");
		return 0;
		}

		@@ -374,6 +382,8 @@ enum {
		OPT_REDIRECT_DIR,
		OPT_INDEX_ON,
		OPT_INDEX_OFF,
		OPT_NFS_EXPORT_ON,
		OPT_NFS_EXPORT_OFF,
		OPT_ERR,
		};

		@@ -385,6 +395,8 @@ static const match_table_t ovl_tokens = {
		{OPT_REDIRECT_DIR, "redirect_dir=%s"},
		{OPT_INDEX_ON, "index=on"},
		{OPT_INDEX_OFF, "index=off"},
		{OPT_NFS_EXPORT_ON, "nfs_export=on"},
		{OPT_NFS_EXPORT_OFF, "nfs_export=off"},
		{OPT_ERR, NULL}
		};

		@@ -491,6 +503,14 @@ static int ovl_parse_opt(char opt, struct ovl_config config)
		config->index = false;
		break;

		case OPT_NFS_EXPORT_ON:
		config->nfs_export = true;
		break;

		case OPT_NFS_EXPORT_OFF:
		config->nfs_export = false;
		break;

		default:
		pr_err("overlayfs: unrecognized mount option \"%s\" or missing value\n", p);
		return -EINVAL;
		@@ -696,13 +716,16 @@ static int ovl_lower_dir(const char name, struct path path,
		*remote = true;

		/*
		* The inodes index feature needs to encode and decode file
		* handles, so it requires that all layers support them.
		* The inodes index feature and NFS export need to encode and decode
		* file handles, so they require that all layers support them.
		*/
		if (ofs->config.index && ofs->config.upperdir &&
		if ((ofs->config.nfs_export \|\|
		(ofs->config.index && ofs->config.upperdir)) &&
		!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);
		ofs->config.nfs_export = false;
		pr_warn("overlayfs: fs on '%s' does not support file handles, falling back to index=off,nfs_export=off.\n",
		name);
		}

		return 0;
		@@ -983,6 +1006,12 @@ static int ovl_make_workdir(struct ovl_fs ofs, struct path workpath)
		pr_warn("overlayfs: upper fs does not support file handles, falling back to index=off.\n");
		}

		/* NFS export of r/w mount depends on index */
		if (ofs->config.nfs_export && !ofs->config.index) {
		pr_warn("overlayfs: NFS export requires \"index=on\", falling back to nfs_export=off.\n");
		ofs->config.nfs_export = false;
		}

		out:
		mnt_drop_write(mnt);
		return err;
		@@ -1141,6 +1170,10 @@ static struct ovl_entry ovl_get_lowerstack(struct super_block sb,
		} else if (!ofs->config.upperdir && stacklen == 1) {
		pr_err("overlayfs: at least 2 lowerdir are needed while upperdir nonexistent\n");
		goto out_err;
		} else if (!ofs->config.upperdir && ofs->config.nfs_export &&
		ofs->config.redirect_follow) {
		pr_warn("overlayfs: NFS export requires \"redirect_dir=nofollow\" on non-upper mount, falling back to nfs_export=off.\n");
		ofs->config.nfs_export = false;
		}

		err = -ENOMEM;
		@@ -1217,6 +1250,7 @@ static int ovl_fill_super(struct super_block sb, void data, int silent)
		goto out_err;

		ofs->config.index = ovl_index_def;
		ofs->config.nfs_export = ovl_nfs_export_def;
		err = ovl_parse_opt((char *) data, &ofs->config);
		if (err)
		goto out_err;
		@@ -1277,8 +1311,13 @@ static int ovl_fill_super(struct super_block sb, void data, int silent)
		}

		/* Show index=off in /proc/mounts for forced r/o mount */
		if (!ofs->indexdir)
		if (!ofs->indexdir) {
		ofs->config.index = false;
		if (ofs->upper_mnt && ofs->config.nfs_export) {
		pr_warn("overlayfs: NFS export requires an index dir, falling back to nfs_export=off.\n");
		ofs->config.nfs_export = false;
		}
		}

		/* Never override disk quota limits or use reserved space */
		cap_lower(cred->cap_effective, CAP_SYS_RESOURCE);

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