[PATCHSET RFC v5 4/8] fuse: allow servers to use iomap for better file IO performance

Darrick J. Wong
2025-09-16T00:19:05Z

Hi all,

This series connects fuse (the userspace filesystem layer) to fs-iomap
to get fuse servers out of the business of handling file I/O themselves.
By keeping the IO path mostly within the kernel, we can dramatically
improve the speed of disk-based filesystems. This enables us to move
all the filesystem metadata parsing code out of the kernel and into
userspace, which means that we can containerize them for security
without losing a lot of performance.

If you're going to start using this code, I strongly recommend pulling
from my git trees, which are linked below.

This has been running on the djcloud for months with no problems. Enjoy!
Comments and questions are, as always, welcome.

--D

kernel git tree:
https://git.kernel.org/cgit/linux/kernel/git/djwong/xfs-linux.git/log/?h=fuse-iomap-fileio
---
Commits in this patchset:
* fuse: implement the basic iomap mechanisms
* fuse_trace: implement the basic iomap mechanisms
* fuse: make debugging configurable at runtime
* fuse: adapt FUSE_DEV_IOC_BACKING_{OPEN,CLOSE} to add new iomap devices
* fuse_trace: adapt FUSE_DEV_IOC_BACKING_{OPEN,CLOSE} to add new iomap devices
* fuse: flush events and send FUSE_SYNCFS and FUSE_DESTROY on unmount
* fuse: create a per-inode flag for toggling iomap
* fuse_trace: create a per-inode flag for toggling iomap
* fuse: isolate the other regular file IO paths from iomap
* fuse: implement basic iomap reporting such as FIEMAP and SEEK_{DATA,HOLE}
* fuse_trace: implement basic iomap reporting such as FIEMAP and SEEK_{DATA,HOLE}
* fuse: implement direct IO with iomap
* fuse_trace: implement direct IO with iomap
* fuse: implement buffered IO with iomap
* fuse_trace: implement buffered IO with iomap
* fuse: implement large folios for iomap pagecache files
* fuse: use an unrestricted backing device with iomap pagecache io
* fuse: advertise support for iomap
* fuse: query filesystem geometry when using iomap
* fuse_trace: query filesystem geometry when using iomap
* fuse: implement fadvise for iomap files
* fuse: invalidate ranges of block devices being used for iomap
* fuse_trace: invalidate ranges of block devices being used for iomap
* fuse: implement inline data file IO via iomap
* fuse_trace: implement inline data file IO via iomap
* fuse: allow more statx fields
* fuse: support atomic writes with iomap
* fuse: disable direct reclaim for any fuse server that uses iomap
---
fs/fuse/fuse_i.h | 172 ++++
fs/fuse/fuse_trace.h | 936 +++++++++++++++++++
fs/fuse/iomap_priv.h | 52 +
include/uapi/linux/fuse.h | 201 ++++
fs/fuse/Kconfig | 48 +
fs/fuse/Makefile | 1
fs/fuse/backing.c | 12
fs/fuse/dev.c | 30 +
fs/fuse/dir.c | 120 ++
fs/fuse/file.c | 133 ++-
fs/fuse/file_iomap.c | 2165 +++++++++++++++++++++++++++++++++++++++++++++
fs/fuse/inode.c | 66 +
fs/fuse/iomode.c | 2
fs/fuse/trace.c | 2
14 files changed, 3892 insertions(+), 48 deletions(-)
create mode 100644 fs/fuse/iomap_priv.h
create mode 100644 fs/fuse/file_iomap.c