Linux: 3.2: Use set_nlink to update i_nlink

As of v3.2-rc1~84^2~1, struct inode.i_nlink is now const to prevent
direct modification.

Signed-off-by: Anders Kaseorg <andersk@mit.edu>
Reviewed-on: http://gerrit.openafs.org/6096
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>
(cherry picked from commit f1dd2d696fb9ab71b4192b156042e0c63019c58a)

Change-Id: I685aa6e8638e8fe864f1a6a7e428dfb6839ebcea
Reviewed-on: http://gerrit.openafs.org/6099
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>

acinclude.m4

@@ -943,6 +943,7 @@ case $AFS_SYSNAME in *_linux* | *_umlinux*)
 		 LINUX_REGISTER_SYSCTL_TABLE_NOFLAG
 		 LINUX_HAVE_DCACHE_LOCK
 		 LINUX_D_COUNT_IS_INT
+		 LINUX_HAVE_SET_NLINK
 
 		 dnl If we are guaranteed that keyrings will work - that is
 		 dnl  a) The kernel has keyrings enabled

src/afs/LINUX/osi_vfsops.c

@@ -439,7 +439,11 @@ void
 vattr2inode(struct inode *ip, struct vattr *vp)
 {
     ip->i_ino = vp->va_nodeid;
+#ifdef HAVE_SET_NLINK
+    set_nlink(ip, vp->va_nlink);
+#else
     ip->i_nlink = vp->va_nlink;
+#endif
     ip->i_blocks = vp->va_blocks;
 #ifdef STRUCT_INODE_HAS_I_BLKBITS
     ip->i_blkbits = AFS_BLKBITS;

src/cf/linux-test4.m4

@@ -618,3 +618,15 @@ AC_DEFUN([LINUX_DOP_D_DELETE_TAKES_CONST], [
 			[define if dentry.d_op->d_delete takes a const argument],
 			[-Werror])
 ])
+
+
+AC_DEFUN([LINUX_HAVE_SET_NLINK], [
+  AC_CHECK_LINUX_BUILD([for set_nlink],
+			[ac_cv_linux_have_set_nlink],
+			[#include <linux/fs.h>],
+			[struct inode _inode;
+			set_nlink(&_inode, 1);],
+			[HAVE_SET_NLINK],
+			[define if set_nlink exists],
+			[-Werror])
+])