On Sun, Aug 10, 2025 at 7:32 AM Rick Macklem <rick.macklem@xxxxxxxxx> wrote: > > On Sun, Aug 10, 2025 at 6:58 AM David Noveck <davenoveck@xxxxxxxxx> wrote: > > > > > > > > On Sat, Aug 9, 2025 at 5:02 PM Rick Macklem <rick.macklem@xxxxxxxxx> wrote: > >> > >> On Sat, Aug 9, 2025 at 1:12 PM David Noveck <davenoveck@xxxxxxxxx> wrote: > >> > > >> > > >> > > >> > On Friday, August 8, 2025, Rick Macklem <rick.macklem@xxxxxxxxx> wrote: > >> >> > >> >> On Fri, Aug 8, 2025 at 8:38 PM Trond Myklebust <trondmy@xxxxxxxxx> wrote: > >> >> > > >> >> > > >> >> > > >> >> > On Fri, Aug 8, 2025 at 9:47 PM Rick Macklem <rick.macklem@xxxxxxxxx> wrote: > >> >> >> > >> >> >> Hi, > >> >> >> > >> >> >> I'm looking at RFC7862 and I cannot find where it > >> >> >> states if the clone_blksize attribute is per-file or > >> >> >> per-file-system. > >> >> >> > >> >> >> If it is not in the RFC, which do others think it is? > >> > > >> > > >> > Before you told us about ZFS, I would have assumed per-fs. > >> > > >> > Given the uncertainty in the spec, you may wind up dealing clients that assume it is per-fs. > >> > > >> > Although this is not a catastrophe, you might want to file an errata report explaining the negative consequences of assuming this is per-fs. It won't get into a spec for a long while but it does provide as much warning as you can right now . > >> > > >> > > >> > > >> >> > >> >> >> (Or maybe, if you have implemented CLONE, > >> >> >> which does your implementation assume?) > >> >> >> > >> >> >> In case you are wondering why I am asking, > >> >> >> it turns out that files in a ZFS volume can have > >> >> >> different block sizes. (It can be changed after the > >> >> >> file system is created.) > >> > > >> > > >> > The guy who allowed that probably thinks it's a helpful feature. Sigh! > >> It's not just a feature change after creation, it turns out to be based > >> on file size as well. A small file gets 512 and a larger one gets a full record > >> (128K on my test system). > >> > >> And, yes, block cloning requires alignment with 512bytes or 128Kbytes > >> depending on the file. > >> > >> I can return 128K for clone_blksize and that will (sub-optimally) handle > >> the 512byte case, but I think it is also possible to increase the record > >> size from 128K-> after the file system has files in it. > >> > >> I'll take a look at the Linux client to try and see if/how it uses > >> clone_blksize. I need to decide if I should always return 128K > >> (or whatever the full recordsize is) or 512 for the small files. > > > > > > I don't see the point of returning anything but 128K given what you said above. > > If a file has to be smaller than 512 to merit the 512 block size, it could still be cloned with a 128k clone_block_size. The spec makes an exception for the last block of a file being shorter than the block size so returning a 512-byte clone_block_size. > I'll be experimenting with it soon. > What I do not know (you could write what I know about ZFS on a > postage stamp;-) is whether the blksize for a file changes as it > grows. > --> So the problem is a file might get 512 because it is small when > first created and then grow large. Again, I do not currently know > what determines the blksize. Whether it is the first write being less > than a record size when created or maybe it does switch to recordsize > (128K in my case) when it grows beyond 128K or ??? > - I do know that ZFS allocates new blocks whenever data is written > to a file, even if the file is not growing. (Which is why it cannot > support ALLOCATE at this time and probably never will.) > > I'll be poking at it. For now, I just do not know, rick I should have done a scan before posting. I just ran a little program that printed out the blksize of every regular file in a ZFS file system. It turns out that the blksize is any exact multiple of 512 up to 128K (the record size for the volume). Since most are C sources or objects, most are less than 128K. If I return 128K, then most files would not be CLONEable unless the CLONE is for the entire file. Of course, I do not currently know how clients actually use clone_blksize either. (Do they check alignment using it before doing a CLONE or ???) I'll be playing around with CLONE for both FreeBSD and Linux in the coming days. I'll post if/when I have useful info, rick > > > >> > >> > >> Thanks for the comments, rick > >> > >> > > >> >> >> > >> > > >> > > >> >> > >> >> >> Thanks, rick > >> >> >> > >> >> > > >> >> > Yes, but since ZFS only supports filesystem level snapshots, and not actual file cloning, does that matter to anything? > >> >> ZFS now has a feature it calls block cloning, which does clone file ranges. > >> >> (It was only added recently. I do not know if the Linux port uses it yet?) > >> >> > >> >> rick > >> >> > >> >> > > >> >> > Cheers > >> >> > Trond > >> >> > >> >> _______________________________________________ > >> >> nfsv4 mailing list -- nfsv4@xxxxxxxx > >> >> To unsubscribe send an email to nfsv4-leave@xxxxxxxx
