Allow use of a write open stateid for reading in the NFSv4 server.

The NFSv4 RFCs give a server the option of allowing the use of an open
stateid for write access to be used for a Read operation.
This patch enables this by default and adds a sysctl to disable it,
for anyone who does not want this capability.
Allowing this is particularily useful for a pNFS Data Server (DS), since
they are not permitted to allow the use of special stateids.
Discovered during recent testing of the pNFS server under development.

MFC after:	2 weeks

1 files changed, 7 insertions, 1 deletions

diff --git a/sys/fs/nfsserver/nfs_nfsdstate.c b/sys/fs/nfsserver/nfs_nfsdstate.c
index 1c2e7d1a762e..f494071171f3 100644
--- a/sys/fs/nfsserver/nfs_nfsdstate.c
+++ b/sys/fs/nfsserver/nfs_nfsdstate.c
@@ -75,6 +75,11 @@ SYSCTL_INT(_vfs_nfsd, OID_AUTO, writedelegifpos, CTLFLAG_RW,
     &nfsrv_writedelegifpos, 0,
     "Issue a write delegation for read opens if possible");
 
+static int	nfsrv_allowreadforwriteopen = 1;
+SYSCTL_INT(_vfs_nfsd, OID_AUTO, allowreadforwriteopen, CTLFLAG_RW,
+    &nfsrv_allowreadforwriteopen, 0,
+    "Allow Reads to be done with Write Access StateIDs");
+
 /*
  * Hash lists for nfs V4.
  */
@@ -1872,7 +1877,8 @@ tryagain:
 		       mystp->ls_flags & NFSLCK_ACCESSBITS)) ||
 		    ((new_stp->ls_flags & (NFSLCK_CHECK|NFSLCK_READACCESS)) ==
 		      (NFSLCK_CHECK | NFSLCK_READACCESS) &&
-		     !(mystp->ls_flags & NFSLCK_READACCESS)) ||
+		     !(mystp->ls_flags & NFSLCK_READACCESS) &&
+		     nfsrv_allowreadforwriteopen == 0) ||
 		    ((new_stp->ls_flags & (NFSLCK_CHECK|NFSLCK_WRITEACCESS)) ==
 		      (NFSLCK_CHECK | NFSLCK_WRITEACCESS) &&
 		     !(mystp->ls_flags & NFSLCK_WRITEACCESS))) {