On 8/23/23 11:07, Miklos Szeredi wrote:
On Tue, 11 Jul 2023 at 06:36, Jiachen Zhang <zhangjiachen.jaycee@xxxxxxxxxxxxx> wrote:Some users may want both the high performance of the writeback_cahe mode and a little bit more consistency among FUSE mounts. Current writeback_cache mode never updates attributes from server, so can never see the file attributes changed by other FUSE mounts, which means 'zero-consisteny'. This commit introduces writeback_cache_v2 mode, which allows the attributes to be updated from server to kernel when the inode is clean and no writeback is in-progressing. FUSE daemons can select this mode by the FUSE_WRITEBACK_CACHE_V2 init flag. In writeback_cache_v2 mode, the server generates official attributes. Therefore, 1. For the cmtime, the cmtime generated by kernel are just temporary values that are never flushed to server by fuse_write_inode(), and they could be eventually updated by the official server cmtime. The mtime-based revalidation of the fc->auto_inval_data mode is also skipped, as the kernel-generated temporary cmtime are likely not equal to the offical server cmtime. 2. For the file size, we expect server updates its file size on FUSE_WRITEs. So we increase fi->attr_version in fuse_writepage_end() to check the staleness of the returning file size. Together with FOPEN_INVAL_ATTR, a FUSE daemon is able to implement close-to-open (CTO) consistency like NFS client implementations.What I'd prefer is mode similar to NFS: getattr flushes pending writes so that server ctime/mtime are always in sync with client. FUSE probably should have done that from the beginning, but at that time I wasn't aware of the NFS solution.
I think it would be good to have flush-on-getattr configurable - systems with a distributed lock manager (DLM) and notifications from server/daemon to kernel should not need it.
Thanks, Bernd
