lws_fsmount: overlayfs apis

CMakeLists.txt

@@ -151,6 +151,8 @@ option(LWS_WITH_FILE_OPS "Support file operations vfs" ON)
 option(LWS_WITH_DETAILED_LATENCY "Record detailed latency stats for each read and write" OFF)
 option(LWS_WITH_UDP "Platform supports UDP" ON)
 option(LWS_WITH_SPAWN "Spawn subprocesses with piped stdin/out/stderr" OFF)
+option(LWS_WITH_FSMOUNT "Overlayfs and fallback mounting apis" OFF)
+
 
 #
 # to use miniz, enable both LWS_WITH_ZLIB and LWS_WITH_MINIZ
@@ -197,6 +199,7 @@ if (LWS_FOR_GITOHASHI)
 	set(LWS_WITH_LWSAC 1)
 	set(LWS_WITH_LEJP_CONF 1)
 	set(LWS_WITH_SPAWN 1)
+	set(LWS_WITH_FSMOUNT 1)
 	set(LWS_WITH_STRUCT_JSON 1)
 	set(LWS_WITH_STRUCT_SQLITE3 1)
 endif()
@@ -232,6 +235,7 @@ if(LWS_WITH_DISTRO_RECOMMENDED)
 	set(LWS_WITH_STRUCT_JSON 1)
 	set(LWS_WITH_STRUCT_SQLITE3 1)
 	set(LWS_WITH_SPAWN 1)
+	set(LWS_WITH_FSMOUNT 1)
 endif()
 
 if (NOT LWS_WITH_NETWORK)
@@ -561,7 +565,8 @@ set(LWS_LIBEVENT_INCLUDE_DIRS CACHE PATH "Path to the libevent include directory
 set(LWS_LIBEVENT_LIBRARIES CACHE PATH "Path to the libevent library")
 set(LWS_GLIB_INCLUDE_DIRS CACHE PATH "Path to the glib include directory")
 set(LWS_GLIB_LIBRARIES CACHE PATH "Path to the glib library")
-
+set(LWS_LIBMOUNT_INCLUDE_DIRS CACHE PATH "Path to the libmount include directory")
+set(LWS_LIBMOUNT_LIBRARIES CACHE PATH "Path to the libmount library")
 
 
 if (NOT LWS_WITH_SSL)
@@ -636,6 +641,23 @@ if (LWS_WITH_HTTP_STREAM_COMPRESSION)
 	set(LWS_WITH_ZLIB 1)
 endif()
 
+if (LWS_WITH_FSMOUNT AND ${CMAKE_SYSTEM_NAME} STREQUAL "Linux")
+	if ("${LWS_LIBMOUNT_LIBRARIES}" STREQUAL "" OR "${LWS_LIBMOUNT_INCLUDE_DIRS}" STREQUAL "")
+
+                # libmount paths (this is only on Linux)
+                #
+                find_path(   LIBMOUNT_INC_PATH NAMES "libmount/libmount.h")
+                find_library(LIBMOUNT_LIB_PATH NAMES "mount")
+	else()
+		set(LIBMOUNT_INC_PATH ${LWS_LIBMOUNT_INCLUDE_DIRS})
+		set(LIBMOUNT_LIB_PATH ${LWS_LIBMOUNT_LIBRARIES})
+	endif()
+
+	if (NOT LIBMOUNT_INC_PATH OR NOT LIBMOUNT_LIB_PATH)
+		message(FATAL_ERROR " Unable to find libmount")
+	endif()
+endif()
+
 if (LWS_WITH_ZLIB AND NOT LWS_WITH_BUNDLED_ZLIB)
 	if ("${LWS_ZLIB_LIBRARIES}" STREQUAL "" OR "${LWS_ZLIB_INCLUDE_DIRS}" STREQUAL "")
 	else()
@@ -1055,6 +1077,11 @@ if (LWS_WITH_SPAWN)
 	list(APPEND SOURCES lib/misc/spawn.c)
 endif()
 
+if (LWS_WITH_FSMOUNT AND ${CMAKE_SYSTEM_NAME} STREQUAL "Linux")
+	list(APPEND SOURCES lib/misc/fsmount.c)
+endif()
+
+
 
 if (LWS_WITH_FILE_OPS)
 	list(APPEND SOURCES lib/core/vfs.c)
@@ -1961,6 +1988,13 @@ if (LWS_WITH_GLIB)
 	list(APPEND LIB_LIST ${GLIB_LIBRARIES})
 endif(LWS_WITH_GLIB)
 
+if (LWS_WITH_FSMOUNT AND ${CMAKE_SYSTEM_NAME} STREQUAL "Linux")
+	message("libmount include dir: ${LIBMOUNT_INC_PATH}")
+	message("libmount libraries: ${LIBMOUNT_LIB_PATH}")
+
+	include_directories("${LIBMOUNT_INC_PATH}")
+	list(APPEND LIB_LIST ${LIBMOUNT_LIB_PATH})
+endif()
 
 
 if (LWS_WITH_SQLITE3)

cmake/lws_config.h.in

@@ -111,6 +111,7 @@
 #cmakedefine LWS_HAVE_EVBACKEND_LINUXAIO
 #cmakedefine LWS_WITH_EXTERNAL_POLL
 #cmakedefine LWS_WITH_FILE_OPS
+#cmakedefine LWS_WITH_FSMOUNT
 #cmakedefine LWS_WITH_FTS
 #cmakedefine LWS_WITH_GENCRYPTO
 #cmakedefine LWS_WITH_GENERIC_SESSIONS

include/libwebsockets/lws-misc.h

@@ -834,3 +834,66 @@ lws_spawn_get_stdfd(struct lws *wsi);
 
 #endif
 
+struct lws_fsmount {
+	const char	*layers_path;	/* where layers live */
+	const char	*overlay_path;	/* where overlay instantiations live */
+
+	char		mp[256];	/* mountpoint path */
+	char		ovname[64];	/* unique name for mount instance */
+	char		distro[64];	/* unique name for layer source */
+
+#if defined(__linux__)
+	const char	*layers[4];	/* distro layers, like "base", "env" */
+#endif
+};
+
+/**
+ * lws_fsmount_mount() - Mounts an overlayfs stack of layers
+ *
+ * \p fsm: struct lws_fsmount specifying the mount layout
+ *
+ * This api is able to assemble up to 4 layer directories on to a mountpoint
+ * using overlayfs mount (Linux only).
+ *
+ * Set fsm.layers_path to the base dir where the layers themselves live, the
+ * entries in fsm.layers[] specifies the relative path to the layer, comprising
+ * fsm.layers_path/fsm.distro/fsm.layers[], with [0] being the deepest, earliest
+ * layer and the rest being progressively on top of [0]; NULL indicates the
+ * layer is unused.
+ *
+ * fsm.overlay_path is the base path of the overlayfs instantiations... empty
+ * dirs must exist at
+ *
+ * fsm.overlay_path/overlays/fsm.ovname/work
+ * fsm.overlay_path/overlays/fsm.ovname/session
+ *
+ * Set fsm.mp to the path of an already-existing empty dir that will be the
+ * mountpoint, this can be whereever you like.
+ *
+ * Overlayfs merges the union of all the contributing layers at the mountpoint,
+ * the mount is writeable but the layer themselves are immutable, all additions
+ * and changes are stored in
+ *
+ * fsm.overlay_path/overlays/fsm.ovname/session
+ *
+ * Returns 0 if mounted OK, nonzero if errors.
+ *
+ * Retain fsm for use with unmounting.
+ */
+LWS_VISIBLE LWS_EXTERN int
+lws_fsmount_mount(struct lws_fsmount *fsm);
+
+/**
+ * lws_fsmount_unmount() - Unmounts an overlayfs dir
+ *
+ * \p fsm: struct lws_fsmount specifying the mount layout
+ *
+ * Unmounts the mountpoint in fsm.mp.
+ *
+ * Delete fsm.overlay_path/overlays/fsm.ovname/session to permanently eradicate
+ * all changes from the time the mountpoint was in use.
+ *
+ * Returns 0 if unmounted OK.
+ */
+LWS_VISIBLE LWS_EXTERN int
+lws_fsmount_unmount(struct lws_fsmount *fsm);

lib/misc/fsmount.c

@@ -0,0 +1,110 @@
+/*
+ * libwebsockets - small server side websockets and web server implementation
+ *
+ * Copyright (C) 2010 - 2020 Andy Green <andy@warmcat.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicefsme, and/or
+ * sell copies of the Software, and to permit persofsm to whom the Software is
+ * furnished to do so, subject to the following conditiofsm:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portiofsm of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ *
+ * Mount and unmount overlayfs mountpoints (linux only)
+ */
+
+#include "private-lib-core.h"
+#include <unistd.h>
+
+#include <libmount/libmount.h>
+
+#include <string.h>
+#include <signal.h>
+
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <fcntl.h>
+
+int
+lws_fsmount_mount(struct lws_fsmount *fsm)
+{
+	struct libmnt_context *ctx;
+	char opts[512];
+	int n, m;
+
+	/*
+	 * Piece together the options for the overlay mount...
+	 */
+
+	n = lws_snprintf(opts, sizeof(opts), "lowerdir=");
+	for (m = LWS_ARRAY_SIZE(fsm->layers) - 1; m >= 0; m--)
+		if (fsm->layers[m]) {
+			if (n != 9)
+				opts[n++] = ':';
+
+			n += lws_snprintf(&opts[n], sizeof(opts) - n,
+					  "%s/%s/%s", fsm->layers_path,
+					  fsm->distro, fsm->layers[m]);
+		}
+
+	n += lws_snprintf(&opts[n], sizeof(opts) - n,
+			  ",upperdir=%s/overlays/%s/session",
+			  fsm->overlay_path, fsm->ovname);
+
+	n += lws_snprintf(&opts[n], sizeof(opts) - n,
+			  ",workdir=%s/overlays/%s/work",
+			  fsm->overlay_path, fsm->ovname);
+
+	ctx = mnt_new_context();
+	if (!ctx)
+		return 1;
+
+	mnt_context_set_fstype(ctx, "overlay");
+	mnt_context_set_options(ctx, opts);
+	mnt_context_set_mflags(ctx, MS_NOATIME /* |MS_NOEXEC */);
+	mnt_context_set_target(ctx, fsm->mp);
+	mnt_context_set_source(ctx, "none");
+
+	lwsl_notice("%s: mount opts %s\n", __func__, opts);
+
+	m = mnt_context_mount(ctx);
+	lwsl_notice("%s: mountpoint %s: %d\n", __func__, fsm->mp, m);
+
+	mnt_free_context(ctx);
+
+	return m;
+}
+
+int
+lws_fsmount_unmount(struct lws_fsmount *fsm)
+{
+	struct libmnt_context *ctx;
+	int m;
+
+	lwsl_notice("%s: %s\n", __func__, fsm->mp);
+
+	ctx = mnt_new_context();
+	if (!ctx)
+		return 1;
+
+	mnt_context_set_target(ctx, fsm->mp);
+
+	m = mnt_context_umount(ctx);
+	mnt_free_context(ctx);
+
+	fsm->mp[0] = '\0';
+
+	return m;
+}