[PATCH nfs-utils v2 3/4] exportfs: Display and document read_io= and write_io=

[Jeff Layton <jlayton@kernel.org>]

Show explicitly-set I/O modes in "exportfs -v" output and document the
new options in exports(5). Warn when exporting if the running kernel,
or no-netlink, means they will be ignored.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 support/include/nfslib.h   |  1 +
 utils/exportfs/exportfs.c  | 34 ++++++++++++++++++++++++++++++++++
 utils/exportfs/exports.man | 22 ++++++++++++++++++++++
 3 files changed, 57 insertions(+)

diff --git a/support/include/nfslib.h b/support/include/nfslib.h
index 7d7aadaed159..51094886a19e 100644
--- a/support/include/nfslib.h
+++ b/support/include/nfslib.h
@@ -79,6 +79,7 @@ struct xprtsec_entry {
  * Per-export I/O modes for read_io=/write_io=. Values must match the
  * kernel's NFSD_IO_* enum (fs/nfsd/nfsd.h). NFSD_IO_UNSET means no
  * option was given; the export follows the server's global setting.
+ * It matches the kernel's NFSD_IO_DEFAULT value.
  */
 #define NFSD_IO_BUFFERED	0
 #define NFSD_IO_DONTCACHE	1
diff --git a/utils/exportfs/exportfs.c b/utils/exportfs/exportfs.c
index ecf66fd07fd1..eb08ce4662f8 100644
--- a/utils/exportfs/exportfs.c
+++ b/utils/exportfs/exportfs.c
@@ -614,6 +614,32 @@ try_proc:
 	return 1;
 }
 
+/*
+ * mountd passes read_io= and write_io= to the kernel only over netlink, and
+ * only to a kernel that takes them.  @test_result is from can_test().
+ */
+static void
+validate_iomode(nfs_export *exp, const char *path, int test_result)
+{
+	static int supported = -1;
+
+	if (exp->m_export.e_read_io == NFSD_IO_UNSET &&
+	    exp->m_export.e_write_io == NFSD_IO_UNSET)
+		return;
+
+	if (supported < 0)
+		supported = test_result == 2 ?
+			    nfsd_export_iomode_supported() : 0;
+	/* nfsd is not loaded, so there is no telling yet */
+	if (supported < 0)
+		return;
+
+	if (!supported)
+		xlog(L_WARNING, "%s: ignoring read_io= and write_io=: %s", path,
+		     no_netlink ? "no-netlink is set" :
+				  "not supported by the running kernel");
+}
+
 static void
 validate_export(nfs_export *exp)
 {
@@ -642,6 +668,8 @@ validate_export(nfs_export *exp)
 	if (!test_result)
 		return;
 
+	validate_iomode(exp, path, test_result);
+
 	/*
 	 * When netlink is available, skip the export_test() probe.
 	 * mountd/exportd will validate exports at cache-fill time.
@@ -838,6 +866,12 @@ dump(int verbose, int export_format)
 				c = dumpopt(c, "no_acl");
 			if (ep->e_flags & NFSEXP_PNFS)
 				c = dumpopt(c, "pnfs");
+			if (ep->e_read_io != NFSD_IO_UNSET)
+				c = dumpopt(c, "read_io=%s",
+					    iomode_name(ep->e_read_io));
+			if (ep->e_write_io != NFSD_IO_UNSET)
+				c = dumpopt(c, "write_io=%s",
+					    iomode_name(ep->e_write_io));
 			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 7f0278fb8d33..ac8bce905573 100644
--- a/utils/exportfs/exports.man
+++ b/utils/exportfs/exports.man
@@ -477,6 +477,28 @@ devices. The default can be explicitly requested with the
 .I no_pnfs
 option.
 
+.TP
+.IR read_io= buffered|dontcache|direct
+This option selects the I/O mode the server uses for NFS READ requests
+to this export:
+.I buffered
+uses the page cache,
+.I dontcache
+uses the page cache but drops the data behind on completion, and
+.I direct
+uses direct I/O.
+If the option is not specified, the export follows the server's global
+setting, which defaults to
+.IR buffered .
+If the kernel does not support per-export I/O modes, the option is
+ignored and a warning is logged.
+
+.TP
+.IR write_io= buffered|dontcache|direct
+This option selects the I/O mode the server uses for NFS WRITE requests
+to this export, with the same values and default as
+.IR read_io= .
+
 .TP
 .IR security_label
 With this option set, clients using NFSv4.2 or higher will be able to

-- 
2.56.0