On Tue, 13 Sep 2022, Dave Chinner wrote: > > Indeed, we know there are many systems out there that mount a > filesystem, preallocate and map the blocks that are allocated to a > large file, unmount the filesysetm, mmap the ranges of the block > device and pass them to RDMA hardware, then have sensor arrays rdma > data directly into the block device. Then when the measurement > application is done they walk the ondisk metadata to remove the > unwritten flags on the extents, mount the filesystem again and > export the file data to a HPC cluster for post-processing..... And this tool doesn't update the i_version? Sounds like a bug. > > So how does the filesystem know whether data the storage contains > for it's files has been modified while it is unmounted and so needs > to change the salt? How does it know that no data is modified while it *is* mounted? Some assumptions have to be made. > > The short answer is that it can't, and so we cannot make assumptions > that a unmount/mount cycle has not changed the filesystem in any > way.... If a mount-count is the best that XFS can do, then that is certainly what it should use. Thanks, NeilBrown
