linux-ext4 - [PATCH 05/22] fuse2fs: always use directio disk reads with fuse2fs

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Message-ID: <175279461123.715479.8914961804310412947.stgit@frogsfrogsfrogs>
Date: Thu, 17 Jul 2025 16:40:40 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: tytso@....edu
Cc: joannelkoong@...il.com, miklos@...redi.hu, John@...ves.net,
 linux-fsdevel@...r.kernel.org, bernd@...ernd.com, linux-ext4@...r.kernel.org,
 neal@...pa.dev
Subject: [PATCH 05/22] fuse2fs: always use directio disk reads with fuse2fs

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

In iomap mode, the kernel writes file data directly to the block device
and does not flush the bdev page cache.  We must open the filesystem in
directio mode to avoid cache coherency issues when reading file data
blocks.  If we can't open the bdev in directio mode, we must not use
iomap.

Signed-off-by: "Darrick J. Wong" <djwong@...nel.org>
---
 misc/fuse2fs.c |   20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/misc/fuse2fs.c b/misc/fuse2fs.c
index 9eb067e1737054..72b9ec837209ca 100644
--- a/misc/fuse2fs.c
+++ b/misc/fuse2fs.c
@@ -1174,6 +1174,9 @@ static void *op_init(struct fuse_conn_info *conn
 	struct fuse_context *ctxt = fuse_get_context();
 	struct fuse2fs *ff = (struct fuse2fs *)ctxt->private_data;
 	ext2_filsys fs = ff->fs;
+#ifdef HAVE_FUSE_IOMAP
+	int was_directio = ff->directio;
+#endif
 	errcode_t err;
 	int ret;

@@ -1196,6 +1199,15 @@ static void *op_init(struct fuse_conn_info *conn
 	if (ff->iomap_state != IOMAP_DISABLED &&
 	    fuse_set_feature_flag(conn, FUSE_CAP_IOMAP))
 		ff->iomap_state = IOMAP_ENABLED;
+	/*
+	 * In iomap mode, the kernel writes file data directly to the block
+	 * device and does not flush the bdev page cache.  We must open the
+	 * filesystem in directio mode to avoid cache coherency issues when
+	 * reading file data.  If we can't open the bdev in directio mode, we
+	 * must not use iomap.
+	 */
+	if (fuse2fs_iomap_enabled(ff))
+		ff->directio = 1;
 #endif

 #if FUSE_VERSION >= FUSE_MAKE_VERSION(3, 0)
@@ -1213,6 +1225,14 @@ static void *op_init(struct fuse_conn_info *conn
 	 */
 	if (!fs) {
 		err = fuse2fs_open(ff, 0);
+#ifdef HAVE_FUSE_IOMAP
+		if (err && fuse2fs_iomap_enabled(ff) && !was_directio) {
+			fuse_unset_feature_flag(conn, FUSE_CAP_IOMAP);
+			ff->iomap_state = IOMAP_DISABLED;
+			ff->directio = 0;
+			err = fuse2fs_open(ff, 0);
+		}
+#endif
 		if (err)
 			goto mount_fail;
 		fs = ff->fs;