linux-ext4 - [PATCH 1/1] fuse2fs: enable caching of iomaps

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Message-ID: <175279461563.716336.4159682025419490591.stgit@frogsfrogsfrogs>
Date: Thu, 17 Jul 2025 16:45:23 -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 1/1] fuse2fs: enable caching of iomaps

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

Cache the iomaps we generate in the kernel for better performance.

Signed-off-by: "Darrick J. Wong" <djwong@...nel.org>
---
 misc/fuse2fs.c |   19 +++++++++++++++++++
 1 file changed, 19 insertions(+)


diff --git a/misc/fuse2fs.c b/misc/fuse2fs.c
index d0478af036a25e..f863042a4db074 100644
--- a/misc/fuse2fs.c
+++ b/misc/fuse2fs.c
@@ -5505,6 +5505,7 @@ static int op_iomap_begin(const char *path, uint64_t nodeid, uint64_t attr_ino,
 {
 	struct fuse_context *ctxt = fuse_get_context();
 	struct fuse2fs *ff = (struct fuse2fs *)ctxt->private_data;
+	struct fuse_session *se = fuse_get_session(ctxt->fuse);
 	struct ext2_inode_large inode;
 	ext2_filsys fs;
 	errcode_t err;
@@ -5560,6 +5561,24 @@ static int op_iomap_begin(const char *path, uint64_t nodeid, uint64_t attr_ino,
 		}
 	}
 
+	/*
+	 * Cache the mapping in the kernel so that we can reuse them for
+	 * subsequent IO.  Note that we have to return NULL mappings to the
+	 * kernel to prompt it to re-try the cache.
+	 */
+	write_iomap->type = FUSE_IOMAP_TYPE_NULL;
+	err = fuse_lowlevel_notify_iomap_upsert(se, nodeid, attr_ino,
+						read_iomap, write_iomap);
+	if (err) {
+		ret = translate_error(fs, attr_ino, err);
+		goto out_unlock;
+	}
+
+	/* Null out the read mapping to encourage a retry. */
+	read_iomap->type = FUSE_IOMAP_TYPE_NULL;
+	read_iomap->dev = FUSE_IOMAP_DEV_NULL;
+	read_iomap->addr = FUSE_IOMAP_NULL_ADDR;
+
 out_unlock:
 	fuse2fs_finish(ff, ret);
 	return ret;