Add way to query creation time of file via cifs xattr

Add parsing for new pseudo-xattr user.cifs.creationtime file
attribute to allow backup and test applications to view
birth time of file on cifs/smb3 mounts.
Signed-off-by: Steve French <steve.french@primarydata.com>

fs/cifs/xattr.c

@@ -34,7 +34,7 @@
 #define MAX_EA_VALUE_SIZE 65535
 #define CIFS_XATTR_CIFS_ACL "system.cifs_acl"
 #define CIFS_XATTR_ATTRIB "cifs.dosattrib"  /* full name: user.cifs.dosattrib */
-
+#define CIFS_XATTR_CREATETIME "cifs.creationtime"  /* user.cifs.creationtime */
 /* BB need to add server (Samba e.g) support for security and trusted prefix */
 
 enum { XATTR_USER, XATTR_CIFS_ACL, XATTR_ACL_ACCESS, XATTR_ACL_DEFAULT };
@@ -169,6 +169,29 @@ static int cifs_attrib_get(struct dentry *dentry,
 	return sizeof(__u32);
 }
 
+static int cifs_creation_time_get(struct dentry *dentry, struct inode *inode,
+				  void *value, size_t size)
+{
+	ssize_t rc;
+	__u64 * pcreatetime;
+
+	rc = cifs_revalidate_dentry_attr(dentry);
+	if (rc)
+		return rc;
+
+	if ((value == NULL) || (size == 0))
+		return sizeof(__u64);
+	else if (size < sizeof(__u64))
+		return -ERANGE;
+
+	/* return dos attributes as pseudo xattr */
+	pcreatetime = (__u64 *)value;
+	*pcreatetime = CIFS_I(inode)->createtime;
+	return sizeof(__u64);
+
+	return rc;
+}
+
 
 static int cifs_xattr_get(const struct xattr_handler *handler,
 			  struct dentry *dentry, struct inode *inode,
@@ -202,6 +225,9 @@ static int cifs_xattr_get(const struct xattr_handler *handler,
 		if (strcmp(name, CIFS_XATTR_ATTRIB) == 0) {
 			rc = cifs_attrib_get(dentry, inode, value, size);
 			break;
+		} else if (strcmp(name, CIFS_XATTR_CREATETIME) == 0) {
+			rc = cifs_creation_time_get(dentry, inode, value, size);
+			break;
 		}
 
 		if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NO_XATTR)