src/StoreFileSystem.h

   1 /*
   2  * $Id$
   3  *
   4  * SQUID Web Proxy Cache          http://www.squid-cache.org/
   5  * ----------------------------------------------------------
   6  *
   7  *  Squid is the result of efforts by numerous individuals from
   8  *  the Internet community; see the CONTRIBUTORS file for full
   9  *  details.   Many organizations have provided support for Squid's
  10  *  development; see the SPONSORS file for full details.  Squid is
  11  *  Copyrighted (C) 2001 by the Regents of the University of
  12  *  California; see the COPYRIGHT file for full details.  Squid
  13  *  incorporates software developed and/or copyrighted by other
  14  *  sources; see the CREDITS file for full details.
  15  *
  16  *  This program is free software; you can redistribute it and/or modify
  17  *  it under the terms of the GNU General Public License as published by
  18  *  the Free Software Foundation; either version 2 of the License, or
  19  *  (at your option) any later version.
  20  *
  21  *  This program is distributed in the hope that it will be useful,
  22  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  23  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  24  *  GNU General Public License for more details.
  25  *
  26  *  You should have received a copy of the GNU General Public License
  27  *  along with this program; if not, write to the Free Software
  28  *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111, USA.
  29  *
  30  * Copyright (c) 2003, Robert Collins <robertc@squid-cache.org>
  31  */
  32
  33 #ifndef SQUID_STOREFILESYSTEM_H
  34 #define SQUID_STOREFILESYSTEM_H
  35
  36 #include "squid-old.h"
  37 #include "Array.h"
  38
  39 /* ****** DOCUMENTATION ***** */
  40
  41 /**
  42  \defgroup FileSystems  Storage Filesystems
  43  *
  44  \section Introduction Introduction
  45  \par
  46  * Traditionally, Squid has always used the Unix filesystem (\link UFS UFS\endlink)
  47  * to store cache objects on disk.  Over the years, the
  48  * poor performance of \link UFS UFS\endlink has become very obvious.  In most
  49  * cases, \link UFS UFS\endlink limits Squid to about 30-50 requests per second.
  50  * Our work indicates that the poor performance is mostly
  51  * due to the synchronous nature of open() and unlink()
  52  * system calls, and perhaps thrashing of inode/buffer caches.
  53  *
  54  \par
  55  * We want to try out our own, customized filesystems with Squid.
  56  * In order to do that, we need a well-defined interface
  57  * for the bits of Squid that access the permanent storage
  58  * devices. We also require tighter control of the replacement
  59  * policy by each storage module, rather than a single global
  60  * replacement policy.
  61  *
  62  \section BuildStructure Build structure
  63  \par
  64  * The storage types live in \em src/fs/. Each subdirectory corresponds
  65  * to the name of the storage type. When a new storage type is implemented
  66  * configure.ac must be updated to autogenerate a Makefile in
  67  * \em src/fs/foo/ from a Makefile.in file.
  68  *
  69  \todo DOCS: add template addition to configure.ac for storage module addition.
  70  \todo DOCS: add template Makefile.am for storage module addition.
  71  *
  72  \par
  73  * configure will take a list of storage types through the
  74  * --enable-store-io parameter. This parameter takes a list of
  75  * space seperated storage types. For example,
  76  * --enable-store-io="ufs coss" .
  77  *
  78  \par
  79  * Each storage type must create an archive file
  80  * in \em src/fs/foo/.a . This file is automatically linked into
  81  * squid at compile time.
  82  *
  83  \par
  84  * Each storage filesystem must inherit from StoreFileSystem and provide
  85  * all virtual function hooks for squid to operate with.
  86  *
  87  \section OperationOfStorageModules Operation of a Storage Module
  88  \par
  89  *    Squid understands the concept of multiple diverse storage directories.
  90  *    Each storage directory provides a caching object store, with object
  91  *    storage, retrieval, indexing and replacement.
  92  *
  93  \par
  94  *    Each open object has associated with it a storeIOState object. The
  95  *    storeIOState object is used to record the state of the current
  96  *    object. Each storeIOState can have a storage module specific data
  97  *    structure containing information private to the storage module.
  98  *
  99  \par
 100  *    Each SwapDir has the concept of a maximum object size. This is used
 101  *    as a basic hint to the storage layer in first choosing a suitable
 102  *    SwapDir. The checkobj function is then called for suitable
 103  *    candidate SwapDirs to find out whether it wants to store a
 104  *    given StoreEntry. A maxobjsize of -1 means 'any size'.
 105  */
 106
 107 class SwapDir;
 108
 109 /**
 110  \ingroup FileSystems
 111  *
 112  * The core API for storage modules this class provides all the hooks
 113  * squid uses to interact with a filesystem IO module.
 114  */
 115 class StoreFileSystem
 116 {
 117
 118 public:
 119     static void SetupAllFs();
 120     static void FsAdd(StoreFileSystem &);
 121     static void FreeAllFs();
 122     static Vector<StoreFileSystem*> const &FileSystems();
 123     typedef Vector<StoreFileSystem*>::iterator iterator;
 124     typedef Vector<StoreFileSystem*>::const_iterator const_iterator;
 125     StoreFileSystem() : initialised(false) {}
 126
 127     virtual ~StoreFileSystem() {}
 128
 129     virtual char const *type () const = 0;
 130     virtual SwapDir *createSwapDir() = 0;
 131     virtual void done() = 0;
 132     virtual void setup() = 0;
 133     // Not implemented
 134     StoreFileSystem(StoreFileSystem const &);
 135     StoreFileSystem &operator=(StoreFileSystem const&);
 136
 137 protected:
 138     bool initialised;
 139     virtual void registerWithCacheManager(void);
 140
 141 private:
 142     static Vector<StoreFileSystem*> &GetFileSystems();
 143     static Vector<StoreFileSystem*> *_FileSystems;
 144     static void RegisterAllFsWithCacheManager(void);
 145 };
 146
 147 // TODO: Kill this typedef!
 148 typedef StoreFileSystem storefs_entry_t;
 149
 150
 151 #endif /* SQUID_STOREFILESYSTEM_H */