linux-ext4 - [PATCH 06/22] fuse2fs: implement directio file reads

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Message-ID: <175279461142.715479.13903075510416571519.stgit@frogsfrogsfrogs>
Date: Thu, 17 Jul 2025 16:40:55 -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 06/22] fuse2fs: implement directio file reads

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

Implement file reads via iomap.  Currently only directio is supported.

Signed-off-by: "Darrick J. Wong" <djwong@...nel.org>
---
 misc/fuse2fs.c |   25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)


diff --git a/misc/fuse2fs.c b/misc/fuse2fs.c
index 72b9ec837209ca..209858aeb9307c 100644
--- a/misc/fuse2fs.c
+++ b/misc/fuse2fs.c
@@ -1274,6 +1274,10 @@ static void *op_init(struct fuse_conn_info *conn
 		goto mount_fail;
 	}
 #endif
+#if defined(HAVE_FUSE_IOMAP) && defined(FUSE_CAP_IOMAP_DIRECTIO)
+	if (fuse2fs_iomap_enabled(ff))
+		fuse_set_feature_flag(conn, FUSE_CAP_IOMAP_DIRECTIO);
+#endif
 
 	/*
 	 * If we're mounting in iomap mode, we need to unmount in op_destroy
@@ -5165,7 +5169,26 @@ static int fuse2fs_iomap_begin_read(struct fuse2fs *ff, ext2_ino_t ino,
 				    uint64_t count, uint32_t opflags,
 				    struct fuse_iomap *read_iomap)
 {
-	return -ENOSYS;
+	errcode_t err;
+
+	if (!(opflags & FUSE_IOMAP_OP_DIRECT))
+		return -ENOSYS;
+
+	/* fall back to slow path for inline data reads */
+	if (inode->i_flags & EXT4_INLINE_DATA_FL)
+		return -ENOSYS;
+
+	/* flush dirty io_channel buffers to disk before iomap reads them */
+	err = io_channel_flush(ff->fs->io);
+	if (err)
+		return translate_error(ff->fs, ino, err);
+
+	if (inode->i_flags & EXT4_EXTENTS_FL)
+		return fuse2fs_iomap_begin_extent(ff, ino, inode, pos, count,
+						  opflags, read_iomap);
+
+	return fuse2fs_iomap_begin_indirect(ff, ino, inode, pos, count,
+					    opflags, read_iomap);
 }
 
 static int fuse2fs_iomap_begin_write(struct fuse2fs *ff, ext2_ino_t ino,