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From: Xin LI <delphij@FreeBSD.org>
Date: Fri, 18 Jan 2013 19:42:09 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
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Subject: svn commit: r245613 - head/sys/fs/nfsserver
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Author: delphij
Date: Fri Jan 18 19:42:08 2013
New Revision: 245613
URL: http://svnweb.freebsd.org/changeset/base/245613

Log:
  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

Modified:
  head/sys/fs/nfsserver/nfs_nfsdserv.c

Modified: head/sys/fs/nfsserver/nfs_nfsdserv.c
==============================================================================
--- head/sys/fs/nfsserver/nfs_nfsdserv.c	Fri Jan 18 19:11:17 2013	(r245612)
+++ head/sys/fs/nfsserver/nfs_nfsdserv.c	Fri Jan 18 19:42:08 2013	(r245613)
@@ -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, 
 			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);