policy: add "most shared path" policies

Like path preserving but walks back the path till a match is found. Should
cover the usecase where someone wants a "less strict" form of path
preservation.

src/policy_msplus.cpp

@@ -0,0 +1,123 @@
+/*
+  Copyright (c) 2016, Antonio SJ Musumeci <trapexit@spawn.link>
+
+  Permission to use, copy, modify, and/or distribute this software for any
+  purpose with or without fee is hereby granted, provided that the above
+  copyright notice and this permission notice appear in all copies.
+
+  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+
+#include "errno.hpp"
+#include "fs.hpp"
+#include "fs_exists.hpp"
+#include "fs_info.hpp"
+#include "fs_path.hpp"
+#include "fs_statvfs_cache.hpp"
+#include "policy.hpp"
+#include "policy_error.hpp"
+#include "rwlock.hpp"
+
+#include <limits>
+#include <string>
+#include <vector>
+
+using std::string;
+using std::vector;
+
+
+namespace msplus
+{
+  static
+  const
+  string*
+  create_1(const Branches &branches_,
+           const string   &fusepath_,
+           const uint64_t  minfreespace_,
+           int            *err_)
+  {
+    int rv;
+    uint64_t lus;
+    string fusepath;
+    fs::info_t info;
+    const Branch *branch;
+    const string *basepath;
+
+    basepath = NULL;
+    lus = std::numeric_limits<uint64_t>::max();
+    for(size_t i = 0, ei = branches_.size(); i != ei; i++)
+      {
+        branch = &branches_[i];
+
+        if(!fs::exists(branch->path,fusepath))
+          error_and_continue(*err_,ENOENT);
+        if(branch->ro_or_nc())
+          error_and_continue(*err_,EROFS);
+        rv = fs::info(&branch->path,&info);
+        if(rv == -1)
+          error_and_continue(*err_,ENOENT);
+        if(info.readonly)
+          error_and_continue(*err_,EROFS);
+        if(info.spaceavail < minfreespace_)
+          error_and_continue(*err_,ENOSPC);
+        if(info.spaceused >= lus)
+          continue;
+
+        lus = info.spaceused;;
+        basepath = &branch->path;
+      }
+
+    return basepath;
+  }
+
+  static
+  int
+  create(const Branches &branches_,
+         const char     *fusepath_,
+         const uint64_t  minfreespace_,
+         vector<string> *paths_)
+  {
+    int error;
+    string fusepath;
+    const string *basepath;
+    rwlock::ReadGuard guard(&branches_.lock);
+
+    error = ENOENT;
+    fusepath = fusepath_;
+    do
+      {
+        basepath = create_1(branches_,fusepath,minfreespace_,&error);
+        if(basepath)
+          break;
+
+        fusepath = fs::path::dirname(fusepath);
+      }
+    while(!fusepath.empty());
+
+    if(basepath == NULL)
+      return (errno=error,-1);
+
+    paths_->push_back(*basepath);
+
+    return 0;
+  }
+}
+
+int
+Policy::Func::msplus(const Category::Enum::Type  type_,
+                     const Branches             &branches_,
+                     const char                 *fusepath_,
+                     const uint64_t              minfreespace_,
+                     vector<string>             *paths_)
+{
+  if(type_ == Category::Enum::create)
+    return msplus::create(branches_,fusepath_,minfreespace_,paths_);
+
+  return Policy::Func::eplus(type_,branches_,fusepath_,minfreespace_,paths_);
+}