Make it possible to force async at server side on new NFS server, similar

to the old one's nfs.nfsrv.async.

Please note that by enabling this option (default is disabled), the system
could potentionally have silent data corruption if the server crashes
before write is committed to non-volatile storage, as the client side have
no way to tell if the data is already written.

Submitted by:	rmacklem
MFC after:	2 weeks

1 files changed, 12 insertions, 1 deletions

diff --git a/sys/fs/nfsserver/nfs_nfsdserv.c b/sys/fs/nfsserver/nfs_nfsdserv.c
index 85fbbd2..307b1f6 100644
--- a/sys/fs/nfsserver/nfs_nfsdserv.c
+++ b/sys/fs/nfsserver/nfs_nfsdserv.c
@@ -55,6 +55,11 @@ extern int nfs_rootfhset;
 extern int nfsrv_enable_crossmntpt;
 #endif	/* !APPLEKEXT */
 
+static int	nfs_async = 0;
+SYSCTL_DECL(_vfs_nfsd);
+SYSCTL_INT(_vfs_nfsd, OID_AUTO, async, CTLFLAG_RW, &nfs_async, 0,
+    "Tell client that writes were synced even though they were not");
+
 /*
  * This list defines the GSS mechanisms supported.
  * (Don't ask me how you get these strings from the RFC stuff like
@@ -912,7 +917,13 @@ nfsrvd_write(struct nfsrv_descript *nd, __unused int isdgram,
 			goto out;
 		NFSM_BUILD(tl, u_int32_t *, 4 * NFSX_UNSIGNED);
 		*tl++ = txdr_unsigned(retlen);
-		if (stable == NFSWRITE_UNSTABLE)
+		/*
+		 * If nfs_async is set, then pretend the write was FILESYNC.
+		 * Warning: Doing this violates RFC1813 and runs a risk
+		 * of data written by a client being lost when the server
+		 * crashes/reboots.
+		 */
+		if (stable == NFSWRITE_UNSTABLE && nfs_async == 0)
 			*tl++ = txdr_unsigned(stable);
 		else
 			*tl++ = txdr_unsigned(NFSWRITE_FILESYNC);