NFS: refactor code for calculating the crc32 hash of a filehandle

We want to be able to display the crc32 hash of the filehandle in
tracepoints.
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/inode.c

@@ -38,7 +38,6 @@
 #include <linux/slab.h>
 #include <linux/compat.h>
 #include <linux/freezer.h>
-#include <linux/crc32.h>
 
 #include <asm/uaccess.h>
 
@@ -1190,7 +1189,7 @@ u32 _nfs_display_fhandle_hash(const struct nfs_fh *fh)
 {
 	/* wireshark uses 32-bit AUTODIN crc and does a bitwise
 	 * not on the result */
-	return ~crc32(0xFFFFFFFF, &fh->data[0], fh->size);
+	return nfs_fhandle_hash(fh);
 }
 
 /*

fs/nfs/internal.h

@@ -5,6 +5,7 @@
 #include "nfs4_fs.h"
 #include <linux/mount.h>
 #include <linux/security.h>
+#include <linux/crc32.h>
 
 #define NFS_MS_MASK (MS_RDONLY|MS_NOSUID|MS_NODEV|MS_NOEXEC|MS_SYNCHRONOUS)
 
@@ -574,3 +575,22 @@ u64 nfs_timespec_to_change_attr(const struct timespec *ts)
 {
 	return ((u64)ts->tv_sec << 30) + ts->tv_nsec;
 }
+
+#ifdef CONFIG_CRC32
+/**
+ * nfs_fhandle_hash - calculate the crc32 hash for the filehandle
+ * @fh - pointer to filehandle
+ *
+ * returns a crc32 hash for the filehandle that is compatible with
+ * the one displayed by "wireshark".
+ */
+static inline u32 nfs_fhandle_hash(const struct nfs_fh *fh)
+{
+	return ~crc32_le(0xFFFFFFFF, &fh->data[0], fh->size);
+}
+#else
+static inline u32 nfs_fhandle_hash(const struct nfs_fh *fh)
+{
+	return 0;
+}
+#endif