fuse2fs: set fuse subtype via argv[0] if possible

If argv[0] ends in "ext[0-9]", set the fuse subtype string to this
value.  This enables us to place fuse2fs at some place in the filesystem
like /sbin/mount.ext2 and have /proc/mounts report the filesystem type
as "fuse.ext2".  This is fairly boring, but it'll make it easier to test
things in fstests.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Link: https://lore.kernel.org/r/174553064709.1160289.11028230202411857669.stgit@frogsfrogsfrogs
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/misc/fuse2fs.c b/misc/fuse2fs.c
index 1029f21..9ffc47c 100644 (file)
--- a/misc/fuse2fs.c
+++ b/misc/fuse2fs.c
@@ -26,6 +26,7 @@
 #endif
 #include <sys/ioctl.h>
 #include <unistd.h>
+#include <ctype.h>
 #ifdef __SET_FOB_FOR_FUSE
 # error Do not set magic value __SET_FOB_FOR_FUSE!!!!
 #endif
@@ -3812,6 +3813,23 @@ static int fuse2fs_opt_proc(void *data, const char *arg,
        return 1;
 }
 
+static const char *get_subtype(const char *argv0)
+{
+       size_t argvlen = strlen(argv0);
+
+       if (argvlen < 4)
+               goto out_default;
+
+       if (argv0[argvlen - 4] == 'e' &&
+           argv0[argvlen - 3] == 'x' &&
+           argv0[argvlen - 2] == 't' &&
+           isdigit(argv0[argvlen - 1]))
+               return &argv0[argvlen - 4];
+
+out_default:
+       return "ext4";
+}
+
 int main(int argc, char *argv[])
 {
        struct fuse_args args = FUSE_ARGS_INIT(argc, argv);
@@ -3960,8 +3978,9 @@ int main(int argc, char *argv[])
        get_random_bytes(&fctx.next_generation, sizeof(unsigned int));
 
        /* Set up default fuse parameters */
-       snprintf(extra_args, BUFSIZ, "-okernel_cache,subtype=ext4,"
+       snprintf(extra_args, BUFSIZ, "-okernel_cache,subtype=%s,"
                 "fsname=%s,attr_timeout=0" FUSE_PLATFORM_OPTS,
+                get_subtype(argv[0]),
                 fctx.device);
        if (fctx.no_default_opts == 0)
                fuse_opt_add_arg(&args, extra_args);