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Date: Tue, 13 Sep 2022 13:30:58 +1000 From: "NeilBrown" <neilb@...e.de> To: "Dave Chinner" <david@...morbit.com> Cc: "Jeff Layton" <jlayton@...nel.org>, "J. Bruce Fields" <bfields@...ldses.org>, "Theodore Ts'o" <tytso@....edu>, "Jan Kara" <jack@...e.cz>, adilger.kernel@...ger.ca, djwong@...nel.org, trondmy@...merspace.com, viro@...iv.linux.org.uk, zohar@...ux.ibm.com, xiubli@...hat.com, chuck.lever@...cle.com, lczerner@...hat.com, brauner@...nel.org, fweimer@...hat.com, linux-man@...r.kernel.org, linux-api@...r.kernel.org, linux-btrfs@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, ceph-devel@...r.kernel.org, linux-ext4@...r.kernel.org, linux-nfs@...r.kernel.org, linux-xfs@...r.kernel.org Subject: Re: [man-pages RFC PATCH v4] statx, inode: document the new STATX_INO_VERSION field 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
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