optimize link_cow eligibility check

src/fs_cow.cpp

@@ -60,13 +60,23 @@ namespace fs
 {
   namespace cow
   {
+    bool
+    is_eligible(const int flags_)
+    {
+      return ((flags_ & O_RDWR) || (flags_ & O_WRONLY));
+    }
+
+    bool
+    is_eligible(const struct stat &st_)
+    {
+      return ((S_ISREG(st_.st_mode)) && (st_.st_nlink > 1));
+    }
+
     bool
     is_eligible(const int          flags_,
                 const struct stat &st_)
     {
-      return (((flags_ & O_RDWR) || (flags_ & O_WRONLY))  &&
-              (S_ISREG(st_.st_mode))                      &&
-              (st_.st_nlink > 1));
+      return (is_eligible(flags_) && is_eligible(st_));
     }
 
     bool
@@ -76,11 +86,14 @@ namespace fs
       int rv;
       struct stat st;
 
-      rv = fs::stat(fullpath_,st);
+      if(!is_eligible(flags_))
+        return false;
+
+      rv = fs::lstat(fullpath_,st);
       if(rv == -1)
         return false;
 
-      return fs::cow::is_eligible(flags_,st);
+      return fs::cow::is_eligible(st);
     }
 
     int

src/fs_cow.hpp

@@ -25,7 +25,10 @@ namespace fs
 {
   namespace cow
   {
+    bool is_eligible(const int flags_);
+    bool is_eligible(const struct stat &st_);
     bool is_eligible(const int flags_, const struct stat &st_);
+
     bool is_eligible(const char *fullpath_, const int flags_);
 
     int  break_link(const char *fullpath_);