"Richard W.M. Jones" <[email protected]> writes: > On Thu, Oct 23, 2025 at 06:45:33PM +0200, Arsen Arsenović wrote: >> "Richard W.M. Jones" <[email protected]> writes: >> >> > I was definitely expecting this one to fail with ENOTSUP or similar. >> > That's with the file copy-allocated-destination-zero-synch.out on ZFS? >> >> Yes - my home directory is on ZoL, and so is ~/tmp. > > It appears this is a limitation of OpenZFS: > > https://github.com/openzfs/zfs/blob/fc519b2c1108b52aaad63e356645f63c2c167f82/module/os/linux/zfs/zpl_file.c#L665
I figured that might be the case. ZFS has a few instances of similar issues. > <quote> > * The original mode=0 (allocate space) behavior can be reasonably emulated > * by checking if enough space exists and creating a sparse file, as real > * persistent space reservation is not possible due to COW, snapshots, etc. > </quote> > > Looking at the code when mode == 0, I believe we hit the second case > (line 707), which seems to sparsify the file and (if that succeeeds) > returns no error :-( > > We should probably add a 'requires' to the test. I think it could > still be a bug in libnbd that we don't fail if fallocate fails, but it > wouldn't have helped here. A reasonable check might be to check whether a truncated file has zero blocks, I suppose. -- Arsen Arsenović
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