On Tue, Jan 14, 2025 at 04:38:03PM -0500, Anna Schumaker wrote: > I've seen a few requests for implementing the NFS v4.2 WRITE_SAME [1] > operation over the last few months [2][3] to accelerate writing > patterns of data on the server, so it's been in the back of my mind > for a future project. I'll need to write some code somewhere so NFS & > NFSD can handle this request. I could keep any implementation internal > to NFS / NFSD, but I'd like to find out if local filesystems would > find this sort of feature useful and if I should put it in the VFS > instead. It would help to know more about what exactly write same does on NFS. Is it like scsi's where you can pass a buffer and it'll write the same buffer over and over across the device? > I was thinking I could keep it simple, and model a function call based > on write(3) / pwrite(3) to write some pattern N times starting at > either the file's current offset or at a user-provide offset. > Something like: > write_pattern(int filedes, const void *pattern, size_t nbytes, size_t count); > pwrite_pattern(int filedes, const void *pattern, size_t nbytes, size_t count, offset_t offset); So yeah, it sounds similar. Assuming nbytes is the size of *pattern, and offset/count are the range to be pwritten? > I could then construct a WRITE_SAME call in the NFS client using this > information. This seems "good enough" to me for what people have asked > for, at least as a client-side interface. It wouldn't really help the > server, which would still need to do several writes in a loop to be > spec-compliant with writing the pattern to an offset inside the > "application data block" [4] structure. I disagree, I think you just volunteered to plumb this pattern writing all the way through to the block layer. ;) > But maybe I'm simplifying this too much, and others would find the > additional application data block fields useful? Or should I keep it > all inside NFS, and call it with an ioctl instead of putting it into > the VFS? io_uring subcommand? But I'd want to know more about what people want to use this for. Assuming you don't just hook up FALLOC_FL_ZERO_RANGE to it and call it a day. :) --D > Thoughts? > Anna > > [1]: https://datatracker.ietf.org/doc/html/rfc7862#section-15.12 > [2]: https://lore.kernel.org/linux-nfs/CAAvCNcByQhbxh9aq_z7GfHx+_=S8zVcr9-04zzdRVLpLbhxxSg@xxxxxxxxxxxxxx/ > [3]: https://lore.kernel.org/linux-nfs/CALWcw=Gg33HWRLCrj9QLXMPME=pnuZx_tE4+Pw8gwutQM4M=vw@xxxxxxxxxxxxxx/ > [4]: https://datatracker.ietf.org/doc/html/rfc7862#section-8.1 >
