subsys/fs/fuse: Support using libfuse3

Support using FUSE v3, instead of FUSE v2.

FUSE v3 has been out for a couple of years now, so most distributions
have it.
But note the FUSE library (and its v3 branch) is currently unmaintained,
and older distributions do not ship it.

Some Linux distros have transitioned their packages away from fuse2.
Which results in less atention in these distros to fuse2, and therefore
a higher likelyhood that there would be distribution issues with the
corresponding packages.
There is also some likelihood the fuse2 packages may be eventually
droped by some of these.

So let's support either version, with a kconfig adapting to either API
and their quirks.

Note that both the fuse2 and fuse3 library code have quite a few
sideeffects on the process that uses it.

By now we continue defaulting to fuse2 as it is the most common.
But users can select to use the v3 if they have an issue w v2 or want
to start trying out using v3.

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>

Author: aescolar

subsys/fs/CMakeLists.txt

@@ -36,7 +36,12 @@ add_subdirectory_ifdef(CONFIG_ZMS  ./zms)
 if(CONFIG_FUSE_FS_ACCESS)
   zephyr_library_named(FS_FUSE)
   find_package(PkgConfig REQUIRED)
-  pkg_search_module(FUSE REQUIRED fuse)
+  if (CONFIG_FUSE_LIBRARY_V3)
+    pkg_search_module(FUSE REQUIRED fuse3)
+    target_compile_options(native_simulator INTERFACE "-DCONFIG_FUSE_LIBRARY_V3")
+  else()
+    pkg_search_module(FUSE REQUIRED fuse)
+  endif()
   list(TRANSFORM FUSE_INCLUDE_DIRS PREPEND "-I")
   target_compile_options(native_simulator INTERFACE ${FUSE_INCLUDE_DIRS})
   list(TRANSFORM FUSE_LIBRARIES PREPEND "-l")

subsys/fs/Kconfig

@@ -106,6 +106,23 @@ config FUSE_FS_ACCESS
 	help
 	  Expose file system partitions to the host system through FUSE.
 
+choice FUSE_LIBRARY_VERSION
+	prompt "Host FUSE library version"
+	depends on FUSE_FS_ACCESS
+	default FUSE_LIBRARY_V2
+
+config FUSE_LIBRARY_V2
+	bool "Use libfuse(2)"
+	help
+	  Use v2 of the host FUSE library.
+
+config FUSE_LIBRARY_V3
+	bool "Use libfuse3"
+	help
+	  Use the host fuse3 library. This may not be available in older distributions.
+
+endchoice
+
 endif # FILE_SYSTEM
 
 if FILE_SYSTEM_LIB_LINK

subsys/fs/fuse_fs_access_bottom.c

@@ -5,7 +5,11 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+#if defined(CONFIG_FUSE_LIBRARY_V3)
+#define FUSE_USE_VERSION 30
+#else
 #define FUSE_USE_VERSION 26
+#endif
 
 #undef _XOPEN_SOURCE
 #define _XOPEN_SOURCE 700
@@ -40,6 +44,9 @@
 
 static pthread_t fuse_thread;
 static struct ffa_op_callbacks *op_callbacks;
+#if defined(CONFIG_FUSE_LIBRARY_V3)
+static sem_t fuse_started; /* semaphore to signal fuse_main has started */
+#endif
 
 /* Pending operation the bottom/fuse thread is queuing into the Zephyr thread */
 struct {
@@ -197,8 +204,14 @@ static bool is_mount_point(const char *path)
 	return strcmp(dirname(dir_path), "/") == 0;
 }
 
+#if defined(CONFIG_FUSE_LIBRARY_V3)
+static int fuse_fs_access_getattr(const char *path, struct stat *st, struct fuse_file_info *fi)
+{
+	NSI_ARG_UNUSED(fi);
+#else
 static int fuse_fs_access_getattr(const char *path, struct stat *st)
 {
+#endif
 	struct ffa_dirent entry;
 	int err;
 
@@ -266,8 +279,13 @@ static int fuse_fs_access_readmount(void *buf, fuse_fill_dir_t filler)
 	st.st_blksize = 0;
 	st.st_blocks = 0;
 
+#if defined(CONFIG_FUSE_LIBRARY_V3)
+	filler(buf, ".", &st, 0, 0);
+	filler(buf, "..", NULL, 0, 0);
+#else
 	filler(buf, ".", &st, 0);
 	filler(buf, "..", NULL, 0);
+#endif
 
 	do {
 		struct op_args_readmount args;
@@ -282,7 +300,11 @@ static int fuse_fs_access_readmount(void *buf, fuse_fill_dir_t filler)
 			break;
 		}
 
+#if defined(CONFIG_FUSE_LIBRARY_V3)
+		filler(buf, &mnt_name[1], &st, 0, 0);
+#else
 		filler(buf, &mnt_name[1], &st, 0);
+#endif
 
 	} while (true);
 
@@ -293,9 +315,16 @@ static int fuse_fs_access_readmount(void *buf, fuse_fill_dir_t filler)
 	return err;
 }
 
+#if defined(CONFIG_FUSE_LIBRARY_V3)
+static int fuse_fs_access_readdir(const char *path, void *buf, fuse_fill_dir_t filler, off_t off,
+				  struct fuse_file_info *fi, enum fuse_readdir_flags flags)
+{
+	NSI_ARG_UNUSED(flags);
+#else
 static int fuse_fs_access_readdir(const char *path, void *buf, fuse_fill_dir_t filler, off_t off,
 				  struct fuse_file_info *fi)
 {
+#endif
 	NSI_ARG_UNUSED(off);
 	NSI_ARG_UNUSED(fi);
 
@@ -345,8 +374,13 @@ static int fuse_fs_access_readdir(const char *path, void *buf, fuse_fill_dir_t f
 	st.st_blksize = 0;
 	st.st_blocks = 0;
 
+#if defined(CONFIG_FUSE_LIBRARY_V3)
+	filler(buf, ".", &st, 0, 0);
+	filler(buf, "..", &st, 0, 0);
+#else
 	filler(buf, ".", &st, 0);
 	filler(buf, "..", &st, 0);
+#endif
 
 	do {
 		err = queue_op(OP_READDIR_READ_NEXT, (void *)&entry);
@@ -366,7 +400,13 @@ static int fuse_fs_access_readdir(const char *path, void *buf, fuse_fill_dir_t f
 			st.st_size = entry.size;
 		}
 
-		if (filler(buf, entry.name, &st, 0)) {
+#if defined(CONFIG_FUSE_LIBRARY_V3)
+		bool full = filler(buf, entry.name, &st, 0, 0);
+#else
+		bool full = filler(buf, entry.name, &st, 0);
+#endif
+
+		if (full) {
 			break;
 		}
 	} while (1);
@@ -468,6 +508,7 @@ static int fuse_fs_access_write(const char *path, const char *buf, size_t size,
 	return -nsi_errno_from_mid(err);
 }
 
+#if !defined(CONFIG_FUSE_LIBRARY_V3)
 static int fuse_fs_access_ftruncate(const char *path, off_t size, struct fuse_file_info *fi)
 {
 	struct op_args_ftruncate args;
@@ -486,9 +527,16 @@ static int fuse_fs_access_ftruncate(const char *path, off_t size, struct fuse_fi
 
 	return -nsi_errno_from_mid(err);
 }
+#endif
 
+#if defined(CONFIG_FUSE_LIBRARY_V3)
+static int fuse_fs_access_truncate(const char *path, off_t size, struct fuse_file_info *fi)
+{
+	NSI_ARG_UNUSED(fi);
+#else
 static int fuse_fs_access_truncate(const char *path, off_t size)
 {
+#endif
 	struct op_args_truncate args;
 	int err;
 
@@ -521,18 +569,35 @@ static int fuse_fs_access_statfs(const char *path, struct statvfs *buf)
 	return 0;
 }
 
+#if defined(CONFIG_FUSE_LIBRARY_V3)
+static int fuse_fs_access_utimens(const char *path, const struct timespec tv[2],
+				  struct fuse_file_info *fi)
+{
+	NSI_ARG_UNUSED(fi);
+#else
 static int fuse_fs_access_utimens(const char *path, const struct timespec tv[2])
 {
+#endif
 	/* dummy */
 	NSI_ARG_UNUSED(path);
 	NSI_ARG_UNUSED(tv);
 	return 0;
 }
 
+#if defined(CONFIG_FUSE_LIBRARY_V3)
+static void *fuse_fs_access_init(struct fuse_conn_info *conn, struct fuse_config *cfg)
+{
+	NSI_ARG_UNUSED(conn);
+	NSI_ARG_UNUSED(cfg);
+
+	sem_post(&fuse_started);
+	return NULL;
+}
+#endif
+
 static struct fuse_operations fuse_fs_access_oper = {
 	.getattr = fuse_fs_access_getattr,
 	.readlink = NULL,
-	.getdir = NULL,
 	.mknod = NULL,
 	.mkdir = fuse_fs_access_mkdir,
 	.unlink = fuse_fs_access_unlink,
@@ -543,7 +608,6 @@ static struct fuse_operations fuse_fs_access_oper = {
 	.chmod = NULL,
 	.chown = NULL,
 	.truncate = fuse_fs_access_truncate,
-	.utime = NULL,
 	.open = fuse_fs_access_open,
 	.read = fuse_fs_access_read,
 	.write = fuse_fs_access_write,
@@ -559,19 +623,24 @@ static struct fuse_operations fuse_fs_access_oper = {
 	.readdir = fuse_fs_access_readdir,
 	.releasedir = NULL,
 	.fsyncdir = NULL,
-	.init = NULL,
+#if defined(CONFIG_FUSE_LIBRARY_V3)
+	.init = fuse_fs_access_init,
+#endif
 	.destroy = NULL,
 	.access = NULL,
 	.create = fuse_fs_access_create,
+#if !defined(CONFIG_FUSE_LIBRARY_V3)
 	.ftruncate = fuse_fs_access_ftruncate,
-	.fgetattr = NULL,
+#endif
 	.lock = NULL,
 	.utimens = fuse_fs_access_utimens,
 	.bmap = NULL,
+#if !defined(CONFIG_FUSE_LIBRARY_V3)
 	.flag_nullpath_ok = 0,
 	.flag_nopath = 0,
 	.flag_utime_omit_ok = 0,
 	.flag_reserved = 0,
+#endif
 	.ioctl = NULL,
 	.poll = NULL,
 	.write_buf = NULL,
@@ -615,15 +684,35 @@ void ffsa_init_bottom(const char *fuse_mountpoint, struct ffa_op_callbacks *op_c
 		nsi_print_error_and_exit("%s is not a directory\n", fuse_mountpoint);
 	}
 
+#if defined(CONFIG_FUSE_LIBRARY_V3)
+	/* Fuse3's fuse_daemonize() changes the cwd to "/" which is a quite undesirable
+	 * side-effect, so we will revert back to where we were once it has initialized
+	 */
+	char *cwd = getcwd(NULL, 0);
+
+	err = sem_init(&fuse_started, 0, 0);
+	if (err) {
+		nsi_print_error_and_exit("Failed to initialize semaphore\n");
+	}
+#endif
+
 	err = sem_init(&op_queue.op_done, 0, 0);
 	if (err) {
 		nsi_print_error_and_exit("Failed to initialize semaphore\n");
 	}
 
 	err = pthread_create(&fuse_thread, NULL, ffsa_main, (void *)fuse_mountpoint);
 	if (err < 0) {
-		nsi_print_error_and_exit("Failed to create thread for fuse_fs_access_main\n");
+		nsi_print_error_and_exit("Failed to create thread for ffsa_main()\n");
+	}
+
+#if defined(CONFIG_FUSE_LIBRARY_V3)
+	if (cwd != NULL) {
+		sem_wait(&fuse_started);
+		chdir(cwd);
+		free(cwd);
 	}
+#endif
 }
 
 void ffsa_cleanup_bottom(const char *fuse_mountpoint)