[PATCH] exportfs: add support for "nowcc" option

[Jeff Layton <jlayton@poochiereds.net>]

This is the userland companion patch for the patch to add a "nowcc"
option to knfsd. This just adds the necessary code to allow userspace
to set that option.

Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
---
 support/include/nfs/export.h |  3 ++-
 support/nfs/exports.c        |  5 +++++
 utils/exportfs/exportfs.c    |  2 ++
 utils/exportfs/exports.man   | 14 ++++++++++++++
 4 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/support/include/nfs/export.h b/support/include/nfs/export.h
index 1194255899bd..68bee5c2f305 100644
--- a/support/include/nfs/export.h
+++ b/support/include/nfs/export.h
@@ -26,7 +26,8 @@
 #define	NFSEXP_CROSSMOUNT	0x4000
 #define NFSEXP_NOACL		0x8000 /* reserved for possible ACL related use */
 #define NFSEXP_V4ROOT		0x10000
-#define NFSEXP_PNFS            0x20000
+#define NFSEXP_PNFS		0x20000
+#define NFSEXP_NOWCC		0x40000
 /*
  * All flags supported by the kernel before addition of the
  * export_features interface:
diff --git a/support/nfs/exports.c b/support/nfs/exports.c
index 0aea6f154f09..791b5f756c9c 100644
--- a/support/nfs/exports.c
+++ b/support/nfs/exports.c
@@ -276,6 +276,7 @@ putexportent(struct exportent *ep)
 	if (ep->e_flags & NFSEXP_NOREADDIRPLUS)
 		fprintf(fp, "nordirplus,");
 	fprintf(fp, "%spnfs,", (ep->e_flags & NFSEXP_PNFS)? "" : "no_");
+	fprintf(fp, "%swcc,", (ep->e_flags & NFSEXP_NOWCC) ? "no" : "");
 	if (ep->e_flags & NFSEXP_FSID) {
 		fprintf(fp, "fsid=%d,", ep->e_fsid);
 	}
@@ -586,6 +587,10 @@ parseopts(char *cp, struct exportent *ep, int warn, int *had_subtree_opt_ptr)
 			setflags(NFSEXP_PNFS, active, ep);
 		else if (!strcmp(opt, "no_pnfs"))
 			clearflags(NFSEXP_PNFS, active, ep);
+		else if (!strcmp(opt, "wcc"))
+			clearflags(NFSEXP_NOWCC, active, ep);
+		else if (!strcmp(opt, "nowcc"))
+			setflags(NFSEXP_NOWCC, active, ep);
 		else if (strncmp(opt, "anonuid=", 8) == 0) {
 			char *oe;
 			ep->e_anonuid = strtol(opt+8, &oe, 10);
diff --git a/utils/exportfs/exportfs.c b/utils/exportfs/exportfs.c
index 87582316b086..a2afc80ee6ea 100644
--- a/utils/exportfs/exportfs.c
+++ b/utils/exportfs/exportfs.c
@@ -823,6 +823,8 @@ dump(int verbose, int export_format)
 				c = dumpopt(c, "no_acl");
 			if (ep->e_flags & NFSEXP_PNFS)
 				c = dumpopt(c, "pnfs");
+			if (ep->e_flags & NFSEXP_NOWCC)
+				c = dumpopt(c, "nowcc");
 			if (ep->e_flags & NFSEXP_FSID)
 				c = dumpopt(c, "fsid=%d", ep->e_fsid);
 			if (ep->e_uuid)
diff --git a/utils/exportfs/exports.man b/utils/exportfs/exports.man
index 93092463153b..9213a228bb04 100644
--- a/utils/exportfs/exports.man
+++ b/utils/exportfs/exports.man
@@ -417,6 +417,20 @@ devices. The default can be explicitly requested with the
 .I no_pnfs
 option.
 
+.TP
+.IR nowcc
+This option disables the collection and reporting of WCC (weak cache
+consistency) data in NFSv3 requests.  RFC 1813 recommends that all
+servers report this information to the clients as it allows the client
+to avoid some extra round trips to the server.  In some underlying
+filesystems however, collecting this data can be cost prohibitive and
+atomicity is difficult to guarantee.  Also, in some client use-cases WCC
+data is ignored or not terribly useful.  The default is to always report
+weak cache consistency data to the client in NFSv3 requests, and can be
+explicitly requested with the
+.I wcc
+option.
+
 .SS User ID Mapping
 .PP
 .B nfsd
-- 
2.4.3