meta: indicate writability of tunables in file mode

All files under .meta (synthetic subtree facilitating
reflection for glusterfs clients, implemented by meta
xlator) were shown as writable, but the vast majority of
them are usable only for querying parameters or stats, not
for setting them. (The exceptions are loglevel and
measure_latency.)

However, one could only find out about this only by trial
and error, or reading the code.

With this change we align file permissions with
tunability, stripping the writable bits for those nodes
which are only for querying.

Also strip writable bits from directory permissions.

updates: gluster#1000
Change-Id: I82954e165ffc31cdf7307f4d990ef60b8154a2e2
Signed-off-by: Csaba Henk <csaba@redhat.com>

xlators/meta/src/meta-helpers.c

@@ -182,22 +182,23 @@ meta_uuid_copy(uuid_t dst, uuid_t src)
 }
 
 static void
-default_meta_iatt_fill(struct iatt *iatt, inode_t *inode, ia_type_t type)
+default_meta_iatt_fill(struct iatt *iatt, inode_t *inode, ia_type_t type,
+                       gf_boolean_t is_tunable)
 {
     struct timeval tv = {};
 
     iatt->ia_type = type;
     switch (type) {
         case IA_IFDIR:
-            iatt->ia_prot = ia_prot_from_st_mode(0755);
+            iatt->ia_prot = ia_prot_from_st_mode(0555);
             iatt->ia_nlink = 2;
             break;
         case IA_IFLNK:
             iatt->ia_prot = ia_prot_from_st_mode(0777);
             iatt->ia_nlink = 1;
             break;
         default:
-            iatt->ia_prot = ia_prot_from_st_mode(0644);
+            iatt->ia_prot = ia_prot_from_st_mode(is_tunable ? 0644 : 0444);
             iatt->ia_nlink = 1;
             break;
     }
@@ -225,7 +226,7 @@ meta_iatt_fill(struct iatt *iatt, inode_t *inode, ia_type_t type)
         return;
 
     if (!ops->iatt_fill)
-        default_meta_iatt_fill(iatt, inode, type);
+        default_meta_iatt_fill(iatt, inode, type, !!ops->file_write);
     else
         ops->iatt_fill(THIS, inode, iatt);
     return;