linux-ext4 - [PATCH 16/16] fuse2fs: avoid fuseblk mode if fuse-iomap support is likely

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Message-ID: <174787198722.1484996.6270446674052578513.stgit@frogsfrogsfrogs>
Date: Wed, 21 May 2025 17:15:01 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: tytso@....edu
Cc: John@...ves.net, linux-ext4@...r.kernel.org, miklos@...redi.hu,
 joannelkoong@...il.com, bernd@...ernd.com, linux-fsdevel@...r.kernel.org
Subject: [PATCH 16/16] fuse2fs: avoid fuseblk mode if fuse-iomap support is
 likely

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

Since fuse in iomap mode guarantees that op_destroy will be called
before umount returns, we don't need to use fuseblk mode to get that
guarantee.  Disable fuseblk mode, which saves us the trouble of closing
and reopening the device.

Signed-off-by: "Darrick J. Wong" <djwong@...nel.org>
---
 misc/fuse2fs.c |   22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)


diff --git a/misc/fuse2fs.c b/misc/fuse2fs.c
index f31aee5af5aad9..28385d654f5e05 100644
--- a/misc/fuse2fs.c
+++ b/misc/fuse2fs.c
@@ -787,6 +787,8 @@ static errcode_t open_fs(struct fuse2fs *ff, int libext2_flags)
 	if (ff->directio)
 		flags |= EXT2_FLAG_DIRECT_IO;
 
+	dbg_printf(ff, "opening with flags=0x%x\n", flags);
+
 	err = ext2fs_open2(ff->device, options, flags, 0, 0, unix_io_manager,
 			   &ff->fs);
 	if (err) {
@@ -6153,6 +6155,18 @@ int main(int argc, char *argv[])
 		ret = 32;
 		goto out;
 	}
+#ifdef HAVE_FUSE_IOMAP
+	if (is_bdev && fuse_discover_iomap()) {
+		/*
+		 * fuse-iomap guarantees that op_destroy is called before the
+		 * filesystem is unmounted, so we don't need fuseblk mode.
+		 * This save us the trouble of reopening the filesystem later,
+		 * and means that fuse2fs itself owns the exclusive lock on the
+		 * block device.
+		 */
+		is_bdev = 0;
+	}
+#endif
 
 	blksize = fctx.fs->blocksize;
 
@@ -6171,14 +6185,14 @@ int main(int argc, char *argv[])
 
 	/* Set up default fuse parameters */
 	snprintf(extra_args, BUFSIZ, "-okernel_cache,subtype=%s,"
-		 "attr_timeout=0" FUSE_PLATFORM_OPTS,
-		 get_subtype(argv[0]));
+		 "attr_timeout=0,fsname=%s" FUSE_PLATFORM_OPTS,
+		 get_subtype(argv[0]), fctx.device);
 	if (fctx.no_default_opts == 0)
 		fuse_opt_add_arg(&args, extra_args);
 
 	if (is_bdev) {
-		snprintf(extra_args, BUFSIZ, "-ofsname=%s,blkdev,blksize=%u",
-			 fctx.device, blksize);
+		snprintf(extra_args, BUFSIZ, "-oblkdev,blksize=%u",
+			 blksize);
 		fuse_opt_add_arg(&args, extra_args);
 	}