conn: prevent duplicate flag conversion in high-level interface

The high-level interface triggers flag conversion twice: once in the
high-level init and once in the low-level init. This caused false
"both 'want' and 'want_ext' are set" errors when using
fuse_set_feature_flag() or fuse_unset_feature_flag().

The existing check for duplicate conversion only worked when 32-bit
flags were set directly. When using the preferred flag manipulation
functions, conn->want and the lower 32 bits of conn->want_ext
would differ, triggering the error.

Fix this by synchronizing conn->want with the lower 32 bits of
conn->want_ext after conversion, ensuring consistent state for
subsequent calls.

Closes: https://github.com/libfuse/libfuse/issues/1171

Signed-off-by: Bernd Schubert <bschubert@ddn.com>

test/hello.c

@@ -0,0 +1,180 @@
+/*
+ * FUSE: Filesystem in Userspace
+ * Copyright (C) 2001-2007  Miklos Szeredi <miklos@szeredi.hu>
+ *
+ * This program can be distributed under the terms of the GNU GPLv2.
+ * See the file COPYING.
+ */
+
+/** @file
+ *
+ * minimal example filesystem using high-level API
+ *
+ * Compile with:
+ *
+ *     gcc -Wall hello.c `pkg-config fuse3 --cflags --libs` -o hello
+ *
+ * ## Source code ##
+ * \include hello.c
+ */
+
+#define FUSE_USE_VERSION 31
+
+#include <fuse.h>
+#include <stdio.h>
+#include <string.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stddef.h>
+#include <assert.h>
+
+/*
+ * Command line options
+ *
+ * We can't set default values for the char* fields here because
+ * fuse_opt_parse would attempt to free() them when the user specifies
+ * different values on the command line.
+ */
+static struct options {
+	const char *filename;
+	const char *contents;
+	int show_help;
+} options;
+
+#define OPTION(t, p) { t, offsetof(struct options, p), 1 }
+static const struct fuse_opt option_spec[] = {
+	OPTION("--name=%s", filename), OPTION("--contents=%s", contents),
+	OPTION("-h", show_help), OPTION("--help", show_help), FUSE_OPT_END
+};
+
+static void *hello_init(struct fuse_conn_info *conn, struct fuse_config *cfg)
+{
+	(void)conn;
+	cfg->kernel_cache = 1;
+
+	/* Test setting flags the old way */
+	conn->want = FUSE_CAP_ASYNC_READ;
+	conn->want &= ~FUSE_CAP_ASYNC_READ;
+
+	return NULL;
+}
+
+static int hello_getattr(const char *path, struct stat *stbuf,
+			 struct fuse_file_info *fi)
+{
+	(void)fi;
+	int res = 0;
+
+	memset(stbuf, 0, sizeof(struct stat));
+	if (strcmp(path, "/") == 0) {
+		stbuf->st_mode = S_IFDIR | 0755;
+		stbuf->st_nlink = 2;
+	} else if (strcmp(path + 1, options.filename) == 0) {
+		stbuf->st_mode = S_IFREG | 0444;
+		stbuf->st_nlink = 1;
+		stbuf->st_size = strlen(options.contents);
+	} else
+		res = -ENOENT;
+
+	return res;
+}
+
+static int hello_readdir(const char *path, void *buf, fuse_fill_dir_t filler,
+			 off_t offset, struct fuse_file_info *fi,
+			 enum fuse_readdir_flags flags)
+{
+	(void)offset;
+	(void)fi;
+	(void)flags;
+
+	if (strcmp(path, "/") != 0)
+		return -ENOENT;
+
+	filler(buf, ".", NULL, 0, FUSE_FILL_DIR_DEFAULTS);
+	filler(buf, "..", NULL, 0, FUSE_FILL_DIR_DEFAULTS);
+	filler(buf, options.filename, NULL, 0, FUSE_FILL_DIR_DEFAULTS);
+
+	return 0;
+}
+
+static int hello_open(const char *path, struct fuse_file_info *fi)
+{
+	if (strcmp(path + 1, options.filename) != 0)
+		return -ENOENT;
+
+	if ((fi->flags & O_ACCMODE) != O_RDONLY)
+		return -EACCES;
+
+	return 0;
+}
+
+static int hello_read(const char *path, char *buf, size_t size, off_t offset,
+		      struct fuse_file_info *fi)
+{
+	size_t len;
+	(void)fi;
+	if (strcmp(path + 1, options.filename) != 0)
+		return -ENOENT;
+
+	len = strlen(options.contents);
+	if (offset < len) {
+		if (offset + size > len)
+			size = len - offset;
+		memcpy(buf, options.contents + offset, size);
+	} else
+		size = 0;
+
+	return size;
+}
+
+static const struct fuse_operations hello_oper = {
+	.init = hello_init,
+	.getattr = hello_getattr,
+	.readdir = hello_readdir,
+	.open = hello_open,
+	.read = hello_read,
+};
+
+static void show_help(const char *progname)
+{
+	printf("usage: %s [options] <mountpoint>\n\n", progname);
+	printf("File-system specific options:\n"
+	       "    --name=<s>          Name of the \"hello\" file\n"
+	       "                        (default: \"hello\")\n"
+	       "    --contents=<s>      Contents \"hello\" file\n"
+	       "                        (default \"Hello, World!\\n\")\n"
+	       "\n");
+}
+
+int main(int argc, char *argv[])
+{
+	int ret;
+	struct fuse_args args = FUSE_ARGS_INIT(argc, argv);
+
+	/* Set defaults -- we have to use strdup so that
+	 *  fuse_opt_parse can free the defaults if other
+	 *  values are specified
+	 */
+	options.filename = strdup("hello");
+	options.contents = strdup("Hello World!\n");
+
+	/* Parse options */
+	if (fuse_opt_parse(&args, &options, option_spec, NULL) == -1)
+		return 1;
+
+	/* When --help is specified, first print our own file-system
+	 * specific help text, then signal fuse_main to show
+	 * additional help (by adding `--help` to the options again)
+	 * without usage: line (by setting argv[0] to the empty
+	 * string)
+	 */
+	if (options.show_help) {
+		show_help(argv[0]);
+		assert(fuse_opt_add_arg(&args, "--help") == 0);
+		args.argv[0][0] = '\0';
+	}
+
+	ret = fuse_main(args.argc, args.argv, &hello_oper, NULL);
+	fuse_opt_free_args(&args);
+	return ret;
+}

test/meson.build

@@ -1,6 +1,6 @@
 # Compile helper programs
 td = []
-foreach prog: [ 'test_write_cache', 'test_setattr' ]
+foreach prog: [ 'test_write_cache', 'test_setattr', 'hello' ]
     td += executable(prog, prog + '.c',
                      include_directories: include_dirs,
                      link_with: [ libfuse ],

test/test_examples.py

@@ -44,8 +44,13 @@ if sys.platform == 'linux':
     options.append('clone_fd')
 
 def invoke_directly(mnt_dir, name, options):
-    cmdline = base_cmdline + [ pjoin(basename, 'example', name),
-                               '-f', mnt_dir, '-o', ','.join(options) ]
+    # Handle test/hello specially since it's not in example/
+    if name.startswith('test/'):
+        path = pjoin(basename, name)
+    else:
+        path = pjoin(basename, 'example', name)
+
+    cmdline = base_cmdline + [ path, '-f', mnt_dir, '-o', ','.join(options) ]
     if name == 'hello_ll':
         # supports single-threading only
         cmdline.append('-s')
@@ -88,7 +93,7 @@ def readdir_inode(dir):
 @pytest.mark.parametrize("cmdline_builder", (invoke_directly, invoke_mount_fuse,
                                              invoke_mount_fuse_drop_privileges))
 @pytest.mark.parametrize("options", powerset(options))
-@pytest.mark.parametrize("name", ('hello', 'hello_ll'))
+@pytest.mark.parametrize("name", ('hello', 'hello_ll', 'test/hello'))
 def test_hello(tmpdir, name, options, cmdline_builder, output_checker):
     logger = logging.getLogger(__name__)
     mnt_dir = str(tmpdir)

test/test_want_conversion.c

@@ -1,11 +1,11 @@
 #include "util.h"
-#include <string.h>
 #define FUSE_USE_VERSION FUSE_MAKE_VERSION(3, 17)
 
 #include "fuse_i.h"
 #include <stdio.h>
 #include <assert.h>
 #include <inttypes.h>
+#include <stdbool.h>
 
 static void print_conn_info(const char *prefix, struct fuse_conn_info *conn)
 {
@@ -13,14 +13,21 @@ static void print_conn_info(const char *prefix, struct fuse_conn_info *conn)
 	       conn->want, conn->want_ext);
 }
 
-static void application_init(struct fuse_conn_info *conn)
+static void application_init_old_style(struct fuse_conn_info *conn)
 {
-	/* Simulate application init */
+	/* Simulate application init the old style */
 	conn->want |= FUSE_CAP_ASYNC_READ;
 	conn->want &= ~FUSE_CAP_SPLICE_READ;
 }
 
-static void test_fuse_fs_init(struct fuse_conn_info *conn)
+static void application_init_new_style(struct fuse_conn_info *conn)
+{
+	/* Simulate application init the new style */
+	fuse_set_feature_flag(conn, FUSE_CAP_ASYNC_READ);
+	fuse_unset_feature_flag(conn, FUSE_CAP_SPLICE_READ);
+}
+
+static void test_fuse_fs_init(struct fuse_conn_info *conn, bool new_style)
 {
 	uint64_t want_ext_default = conn->want_ext;
 	uint32_t want_default = fuse_lower_32_bits(conn->want_ext);
@@ -31,18 +38,22 @@ static void test_fuse_fs_init(struct fuse_conn_info *conn)
 
 	conn->want = want_default;
 
-	application_init(conn);
+	if (new_style)
+		application_init_new_style(conn);
+	else
+		application_init_old_style(conn);
 
 	rc = convert_to_conn_want_ext(conn, want_ext_default, want_default);
 	assert(rc == 0);
 }
 
-static void test_do_init(struct fuse_conn_info *conn)
+static void test_do_init(struct fuse_conn_info *conn, bool new_style)
 {
 	/* Initial setup */
 	conn->capable_ext = FUSE_CAP_SPLICE_READ | FUSE_CAP_SPLICE_WRITE |
 			    FUSE_CAP_SPLICE_MOVE | FUSE_CAP_POSIX_LOCKS |
-			    FUSE_CAP_FLOCK_LOCKS | FUSE_CAP_EXPORT_SUPPORT;
+			    FUSE_CAP_FLOCK_LOCKS | FUSE_CAP_EXPORT_SUPPORT |
+			    FUSE_CAP_ASYNC_READ;
 	conn->capable = fuse_lower_32_bits(conn->capable_ext);
 	conn->want_ext = conn->capable_ext;
 
@@ -55,7 +66,7 @@ static void test_do_init(struct fuse_conn_info *conn)
 	conn->want = want_default;
 	conn->capable = fuse_lower_32_bits(conn->capable_ext);
 
-	test_fuse_fs_init(conn);
+	test_fuse_fs_init(conn, new_style);
 
 	rc = convert_to_conn_want_ext(conn, want_ext_default, want_default);
 	assert(rc == 0);
@@ -82,7 +93,8 @@ static void test_want_conversion_basic(void)
 	struct fuse_conn_info conn = { 0 };
 
 	printf("\nTesting basic want conversion:\n");
-	test_do_init(&conn);
+	test_do_init(&conn, false);
+	test_do_init(&conn, true);
 	print_conn_info("After init", &conn);
 }