[$] Supporting NFS v4.2 WRITE_SAME

At the 2025 Linux Storage, Filesystem, Memory Management, and BPF Summit(LSFMM+BPF), Anna Schumaker led a discussion about implementing the NFSv4.2 WRITE_SAMEcommand in both the NFS client and server. WRITE_SAME ismeant to write large amounts of identical data (e.g. zeroes) to the serverwithout actually needing to transfer all of it over the wire. In her topicproposal, Schumaker wondered whether other filesystems needed thefunctionality, so that it should be implemented at the virtual filesystem(VFS) layer, or whether it should simply be handled as an NFS-specific ioctl().