Re: [PATCH 2/6] NFSD: Apply per-export I/O modes to READ and WRITE

[Chuck Lever]

On 10/27/26 12:45 PM, Jeff Layton wrote:
> Resolve each export's effective I/O mode (explicit setting, else the
> global io_cache_read/write knob) in nfsd_iter_read and nfsd_vfs_write,
> and skip splice for reads on exports whose effective read mode is not
> buffered. Update the debugfs knob comments to match.

[ ... ]

> -	if (file->f_op->splice_read && nfsd_read_splice_ok(rqstp))
> +	if (file->f_op->splice_read && nfsd_read_splice_ok(rqstp) &&
> +	    nfsd_read_iomode(fhp->fh_export) == NFSD_IO_BUFFERED)
>  		err = nfsd_splice_read(rqstp, fhp, file, offset, count, eof);

nfsd_io_cache_read_set() still sets nfsd_disable_splice_read whenever
the global knob is switched to dontcache or direct, so
nfsd_read_splice_ok() returns false before this per-export test is
reached. An export pinned to riomode=buffered on such a server never
gets splice; it falls through to nfsd_iter_read() and does vector
buffered reads. The same applies to the splice_ok decisions in
nfsd4_encode_read() and nfsd4_encode_read_plus_data().

Patch 3/6 says an explicit per-export setting pins that export's
IO mode "regardless of the global knob", and that isn't quite true
now for the buffered case.

I need to think carefully about the interaction between the "disable
splice" setting, which is global, and the per-export I/O setting.

Separately, on the names of the export options: "riomode" and
"wiomode" are hard to read, and "mode" might suggest "permission bits"
to an administrator. How about read_io= and write_io= instead? They
follow the underscore style of the other multi-word export options
(no_subtree_check, root_squash, security_label) and read naturally:

  /srv/data  client(rw,read_io=direct,write_io=dontcache)

The values buffered, dontcache, and direct then carry the meaning
without "cache" or "mode" in the name.

The name appears in the exports syntax, the nfsd.export/content
output, the netlink YAML spec, and the forthcoming nfs-utils series,
so it's worth settling before v2 and before the nfs-utils side gets
merged.


-- 
Chuck Lever (Come to NFS bake-a-thon! https://nfsv4bat.org)