linux-ext4 - [PATCH 2/3] fuse2fs: set fuse subtype via argv[0] if possible

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Message-ID: <174553064709.1160289.11028230202411857669.stgit@frogsfrogsfrogs>
Date: Thu, 24 Apr 2025 14:40:31 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: tytso@....edu
Cc: linux-ext4@...r.kernel.org
Subject: [PATCH 2/3] fuse2fs: set fuse subtype via argv[0] if possible

From: Darrick J. Wong <djwong@...nel.org>

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@...nel.org>
---
 misc/fuse2fs.c |   21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/misc/fuse2fs.c b/misc/fuse2fs.c
index 245d2b3b916686..991a9f6733148d 100644
--- 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);
@@ -3954,8 +3972,9 @@ 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);