linux-ext4 - [PATCH] fuse2fs: open read-only when ro option and image non-writable

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Message-Id: <20251016200206.3035-1-dave.dykstra@cern.ch>
Date: Thu, 16 Oct 2025 15:02:06 -0500
From: Dave Dykstra <dave.dykstra@...n.ch>
To: linux-ext4@...r.kernel.org
Cc: Dave Dykstra <dave.dykstra@...n.ch>,
	Dave Dykstra <2129743+DrDaveD@...rs.noreply.github.com>
Subject: [PATCH] fuse2fs: open read-only when ro option and image non-writable

This opens the image read-only when an ro option is given and the
image is not writable.  If it is then found that a journal recovery
is needed, an error is returned then.

The ret value is set to 4 after the option checks so that if there's
an error resulting in "goto out" it won't print an error about
unrecognized options.

Also submitted as PR https://github.com/tytso/e2fsprogs/pull/250
for the issue https://github.com/tytso/e2fsprogs/issues/244.

Replaces 
    https://lore.kernel.org/linux-ext4/20251010214735.22683-1-dave.dykstra@cern.ch/T/#u
    https://lore.kernel.org/linux-ext4/175798064776.350013.6744611652039454651.stgit@frogsfrogsfrogs/#t

Signed-off-by: Dave Dykstra <2129743+DrDaveD@...rs.noreply.github.com>
---
 misc/fuse2fs.c | 27 +++++++++++++++++++++++----
 1 file changed, 23 insertions(+), 4 deletions(-)

diff --git a/misc/fuse2fs.c b/misc/fuse2fs.c
index cb5620c7..2ae2fc1a 100644
--- a/misc/fuse2fs.c
+++ b/misc/fuse2fs.c
@@ -4696,9 +4696,19 @@ int main(int argc, char *argv[])
 	err = ext2fs_open2(fctx.device, options, flags, 0, 0, unix_io_manager,
 			   &global_fs);
 	if (err) {
-		err_printf(&fctx, "%s.\n", error_message(err));
-		err_printf(&fctx, "%s\n", _("Please run e2fsck -fy."));
-		goto out;
+		if (((err == EACCES) || (err == EPERM)) && fctx.ro) {
+			// read-only requested and don't have write access
+			dbg_printf(&fctx, "%s: %s\n", __func__,
+ _("Permission denied with writable, trying without.\n"));
+			flags &= ~EXT2_FLAG_RW;
+			err = ext2fs_open2(fctx.device, options, flags, 0, 0, 
+					   unix_io_manager, &global_fs);
+		}
+		if (err) {
+			err_printf(&fctx, "%s.\n", error_message(err));
+			err_printf(&fctx, "%s\n", _("Please run e2fsck -fy."));
+			goto out;
+		}
 	}
 	fctx.fs = global_fs;
 	global_fs->priv_data = &fctx;
@@ -4741,6 +4751,8 @@ int main(int argc, char *argv[])
 		goto out;
 	}
 
+	ret = 4;
+
 	if (global_fs->super->s_state & EXT2_ERROR_FS) {
 		err_printf(&fctx, "%s\n",
  _("Errors detected; running e2fsck is required."));
@@ -4760,6 +4772,11 @@ int main(int argc, char *argv[])
  _("Mounting read-only without recovering journal."));
 			fctx.ro = 1;
 			global_fs->flags &= ~EXT2_FLAG_RW;
+		} else if (fctx.ro && !(flags & EXT2_FLAG_RW)) {
+			err_printf(&fctx, "%s\n",
+ _("Journal needs recovery but filesystem could not be opened read-write."));
+			err_printf(&fctx, "%s\n", _("Please run e2fsck -fy."));
+			goto out;
 		} else {
 			log_printf(&fctx, "%s\n", _("Recovering journal."));
 			err = ext2fs_run_ext3_journal(&global_fs);
@@ -4833,8 +4850,10 @@ int main(int argc, char *argv[])
 	if (fctx.no_default_opts == 0)
 		fuse_opt_add_arg(&args, extra_args);
 
-	if (fctx.ro)
+	if (fctx.ro) {
+		/* This is in case ro was implied above and not passed in */
 		fuse_opt_add_arg(&args, "-oro");
+	}
 
 	if (fctx.fakeroot) {
 #ifdef HAVE_MOUNT_NODEV
-- 
2.43.5