Hi all, When iomap is enabled for a fuse file, we try to keep as much of the file IO path in the kernel as we possibly can. That means no calling out to the fuse server in the IO path when we can avoid it. However, the existing FUSE architecture defers all file attributes to the fuse server -- [cm]time updates, ACL metadata management, set[ug]id removal, and permissions checking thereof, etc. We'd really rather do all these attribute updates in the kernel, and only push them to the fuse server when it's actually necessary (e.g. fsync). Furthermore, the POSIX ACL code has the weird behavior that if the access ACL can be represented entirely by i_mode bits, it will change the mode and delete the ACL, which fuse servers generally don't seem to implement. IOWs, we want consistent and correct (as defined by fstests) behavior of file attributes in iomap mode. Let's make the kernel manage all that and push the results to userspace as needed. This improves performance even further, since it's sort of like writeback_cache mode but more aggressive. If you're going to start using this code, I strongly recommend pulling from my git trees, which are linked below. Comments and questions are, as always, welcome. e2fsprogs git tree: https://git.kernel.org/cgit/linux/kernel/git/djwong/e2fsprogs.git/log/?h=fuse2fs-iomap-attrs --- Commits in this patchset: * fuse2fs: skip permission checking on utimens when iomap is enabled * fuse2fs: let the kernel tell us about acl/mode updates * fuse2fs: better debugging for file mode updates * fuse2fs: debug timestamp updates * fuse2fs: use coarse timestamps for iomap mode * fuse2fs: add tracing for retrieving timestamps * fuse2fs: enable syncfs * fuse2fs: skip the gdt write in op_destroy if syncfs is working --- misc/fuse2fs.c | 237 ++++++++++++++++++++++++++++++++++++++++---------------- misc/fuse4fs.c | 193 ++++++++++++++++++++++++++++++++-------------- 2 files changed, 304 insertions(+), 126 deletions(-)
