src/StoreFileSystem.h

   1 /*
   2  * SQUID Web Proxy Cache          http://www.squid-cache.org/
   3  * ----------------------------------------------------------
   4  *
   5  *  Squid is the result of efforts by numerous individuals from
   6  *  the Internet community; see the CONTRIBUTORS file for full
   7  *  details.   Many organizations have provided support for Squid's
   8  *  development; see the SPONSORS file for full details.  Squid is
   9  *  Copyrighted (C) 2001 by the Regents of the University of
  10  *  California; see the COPYRIGHT file for full details.  Squid
  11  *  incorporates software developed and/or copyrighted by other
  12  *  sources; see the CREDITS file for full details.
  13  *
  14  *  This program is free software; you can redistribute it and/or modify
  15  *  it under the terms of the GNU General Public License as published by
  16  *  the Free Software Foundation; either version 2 of the License, or
  17  *  (at your option) any later version.
  18  *
  19  *  This program is distributed in the hope that it will be useful,
  20  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  21  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  22  *  GNU General Public License for more details.
  23  *
  24  *  You should have received a copy of the GNU General Public License
  25  *  along with this program; if not, write to the Free Software
  26  *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111, USA.
  27  *
  28  * Copyright (c) 2003, Robert Collins <robertc@squid-cache.org>
  29  */
  30
  31 #ifndef SQUID_STOREFILESYSTEM_H
  32 #define SQUID_STOREFILESYSTEM_H
  33
  34 #include "Array.h"
  35
  36 /* ****** DOCUMENTATION ***** */
  37
  38 /**
  39  \defgroup FileSystems  Storage Filesystems
  40  *
  41  \section Introduction Introduction
  42  \par
  43  * Traditionally, Squid has always used the Unix filesystem (\link UFS UFS\endlink)
  44  * to store cache objects on disk.  Over the years, the
  45  * poor performance of \link UFS UFS\endlink has become very obvious.  In most
  46  * cases, \link UFS UFS\endlink limits Squid to about 30-50 requests per second.
  47  * Our work indicates that the poor performance is mostly
  48  * due to the synchronous nature of open() and unlink()
  49  * system calls, and perhaps thrashing of inode/buffer caches.
  50  *
  51  \par
  52  * We want to try out our own, customized filesystems with Squid.
  53  * In order to do that, we need a well-defined interface
  54  * for the bits of Squid that access the permanent storage
  55  * devices. We also require tighter control of the replacement
  56  * policy by each storage module, rather than a single global
  57  * replacement policy.
  58  *
  59  \section BuildStructure Build structure
  60  \par
  61  * The storage types live in \em src/fs/. Each subdirectory corresponds
  62  * to the name of the storage type. When a new storage type is implemented
  63  * configure.ac must be updated to autogenerate a Makefile in
  64  * \em src/fs/foo/ from a Makefile.in file.
  65  *
  66  \todo DOCS: add template addition to configure.ac for storage module addition.
  67  \todo DOCS: add template Makefile.am for storage module addition.
  68  *
  69  \par
  70  * configure will take a list of storage types through the
  71  * --enable-store-io parameter. This parameter takes a list of
  72  * space seperated storage types. For example,
  73  * --enable-store-io="ufs coss" .
  74  *
  75  \par
  76  * Each storage type must create an archive file
  77  * in \em src/fs/foo/.a . This file is automatically linked into
  78  * squid at compile time.
  79  *
  80  \par
  81  * Each storage filesystem must inherit from StoreFileSystem and provide
  82  * all virtual function hooks for squid to operate with.
  83  *
  84  \section OperationOfStorageModules Operation of a Storage Module
  85  \par
  86  *    Squid understands the concept of multiple diverse storage directories.
  87  *    Each storage directory provides a caching object store, with object
  88  *    storage, retrieval, indexing and replacement.
  89  *
  90  \par
  91  *    Each open object has associated with it a storeIOState object. The
  92  *    storeIOState object is used to record the state of the current
  93  *    object. Each storeIOState can have a storage module specific data
  94  *    structure containing information private to the storage module.
  95  *
  96  \par
  97  *    Each SwapDir has the concept of a maximum object size. This is used
  98  *    as a basic hint to the storage layer in first choosing a suitable
  99  *    SwapDir. The checkobj function is then called for suitable
 100  *    candidate SwapDirs to find out whether it wants to store a
 101  *    given StoreEntry. A maxobjsize of -1 means 'any size'.
 102  */
 103
 104 class SwapDir;
 105
 106 /**
 107  \ingroup FileSystems
 108  *
 109  * The core API for storage modules this class provides all the hooks
 110  * squid uses to interact with a filesystem IO module.
 111  */
 112 class StoreFileSystem
 113 {
 114
 115 public:
 116     static void SetupAllFs();
 117     static void FsAdd(StoreFileSystem &);
 118     static void FreeAllFs();
 119     static Vector<StoreFileSystem*> const &FileSystems();
 120     typedef Vector<StoreFileSystem*>::iterator iterator;
 121     typedef Vector<StoreFileSystem*>::const_iterator const_iterator;
 122     StoreFileSystem() : initialised(false) {}
 123
 124     virtual ~StoreFileSystem() {}
 125
 126     virtual char const *type () const = 0;
 127     virtual SwapDir *createSwapDir() = 0;
 128     virtual void done() = 0;
 129     virtual void setup() = 0;
 130     // Not implemented
 131     StoreFileSystem(StoreFileSystem const &);
 132     StoreFileSystem &operator=(StoreFileSystem const&);
 133
 134 protected:
 135     bool initialised;
 136     virtual void registerWithCacheManager(void);
 137
 138 private:
 139     static Vector<StoreFileSystem*> &GetFileSystems();
 140     static Vector<StoreFileSystem*> *_FileSystems;
 141     static void RegisterAllFsWithCacheManager(void);
 142 };
 143
 144 // TODO: Kill this typedef!
 145 typedef StoreFileSystem storefs_entry_t;
 146
 147 #endif /* SQUID_STOREFILESYSTEM_H */