fuse_main(): extend support for printing help

There's now a way to inhibit the "usage" line (which actually got lost
in commit 225c12aebf2d), which makes it easier for simply file-systems
to generate good-looking --help output.

1 files changed, 66 insertions, 10 deletions

diff --git a/example/hello.c b/example/hello.c
index 3c24c8b..bf6ccf4 100644
--- a/example/hello.c
+++ b/example/hello.c
@@ -42,9 +42,31 @@
 #include <string.h>
 #include <errno.h>
 #include <fcntl.h>
+#include <stddef.h>
+#include <assert.h>
 
-static const char *hello_str = "Hello World!\n";
-static const char *hello_path = "/hello";
+/**
+ * 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 int hello_getattr(const char *path, struct stat *stbuf)
 {
@@ -54,10 +76,10 @@ static int hello_getattr(const char *path, struct stat *stbuf)
 	if (strcmp(path, "/") == 0) {
 		stbuf->st_mode = S_IFDIR | 0755;
 		stbuf->st_nlink = 2;
-	} else if (strcmp(path, hello_path) == 0) {
+	} else if (strcmp(path+1, options.filename) == 0) {
 		stbuf->st_mode = S_IFREG | 0444;
 		stbuf->st_nlink = 1;
-		stbuf->st_size = strlen(hello_str);
+		stbuf->st_size = strlen(options.contents);
 	} else
 		res = -ENOENT;
 
@@ -77,14 +99,14 @@ static int hello_readdir(const char *path, void *buf, fuse_fill_dir_t filler,
 
 	filler(buf, ".", NULL, 0, 0);
 	filler(buf, "..", NULL, 0, 0);
-	filler(buf, hello_path + 1, NULL, 0, 0);
+	filler(buf, options.filename, NULL, 0, 0);
 
 	return 0;
 }
 
 static int hello_open(const char *path, struct fuse_file_info *fi)
 {
-	if (strcmp(path, hello_path) != 0)
+	if (strcmp(path+1, options.filename) != 0)
 		return -ENOENT;
 
 	if ((fi->flags & 3) != O_RDONLY)
@@ -98,14 +120,14 @@ static int hello_read(const char *path, char *buf, size_t size, off_t offset,
 {
 	size_t len;
 	(void) fi;
-	if(strcmp(path, hello_path) != 0)
+	if(strcmp(path+1, options.filename) != 0)
 		return -ENOENT;
 
-	len = strlen(hello_str);
+	len = strlen(options.contents);
 	if (offset < len) {
 		if (offset + size > len)
 			size = len - offset;
-		memcpy(buf, hello_str + offset, size);
+		memcpy(buf, options.contents + offset, size);
 	} else
 		size = 0;
 
@@ -119,7 +141,41 @@ static struct fuse_operations hello_oper = {
 	.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[])
 {
-	return fuse_main(argc, argv, &hello_oper, NULL);
+	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] = (char*) "";
+	}
+
+	return fuse_main(args.argc, args.argv, &hello_oper, NULL);
 }