On Mon, Jan 06, 2025 at 10:14:35PM -0800, Christoph Hellwig wrote: > On Mon, Jan 06, 2025 at 11:46:39AM -0800, Darrick J. Wong wrote: > > That sounds brittle -- even if someday a FALLOC_FL_WRITE_ZEROES gets > > merged into the kernel, if anything perturbs the file mapping (e.g. > > background backup process reflinks the file) then you immediately become > > vulnerable to these crash integrity problems without notice. > > > > (Unless you're actually getting leases on the file ranges and reacting > > appropriately when the leases break...) > > They way I understood the description they have a user space program > exposing the XFS file over the network. So if a change to the mapping > happens (e.g. due to defragmentation) they would in the worst case pay > the cost of an allocation transaction. > > That is if they are really going through the normal kernel file > abstraction and don't try to bypass it by say abusing FIEMAP > information, in which case all hope is lost and the scheme has no chance > of reliably working, unless we add ioctls to expose the pNFS layouts > to userspace and they use that instead of FIEMAP. I get this funny feeling that a lot of programs might like to lease space and get told by the kernel when someone wants/took it back. Swapfiles and lilo ftw. --D
