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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111, USA.
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/* ****** DOCUMENTATION ***** */
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\defgroup FileSystems Storage Filesystems
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\section Introduction Introduction
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* Traditionally, Squid has always used the Unix filesystem (\link UFS UFS\endlink)
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* to store cache objects on disk. Over the years, the
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* poor performance of \link UFS UFS\endlink has become very obvious. In most
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* cases, \link UFS UFS\endlink limits Squid to about 30-50 requests per second.
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* Our work indicates that the poor performance is mostly
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* due to the synchronous nature of open() and unlink()
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* system calls, and perhaps thrashing of inode/buffer caches.
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* We want to try out our own, customized filesystems with Squid.
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* In order to do that, we need a well-defined interface
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* for the bits of Squid that access the permanent storage
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* devices. We also require tighter control of the replacement
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* policy by each storage module, rather than a single global
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\section BuildStructure Build structure
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* The storage types live in \em src/fs/. Each subdirectory corresponds
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* to the name of the storage type. When a new storage type is implemented
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* configure.in must be updated to autogenerate a Makefile in
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* \em src/fs/foo/ from a Makefile.in file.
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\todo DOCS: add template addition to configure.in for storage module addition.
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\todo DOCS: add template Makefile.am for storage module addition.
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* configure will take a list of storage types through the
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* --enable-store-io parameter. This parameter takes a list of
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* space seperated storage types. For example,
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* --enable-store-io="ufs coss" .
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* Each storage type must create an archive file
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* in \em src/fs/foo/.a . This file is automatically linked into
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* squid at compile time.
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* Each storage filesystem must inherit from StoreFileSystem and provide
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* all virtual function hooks for squid to operate with.
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\section OperationOfStorageModules Operation of a Storage Module
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* Squid understands the concept of multiple diverse storage directories.
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* Each storage directory provides a caching object store, with object
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* storage, retrieval, indexing and replacement.
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* Each open object has associated with it a storeIOState object. The
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* storeIOState object is used to record the state of the current
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* object. Each storeIOState can have a storage module specific data
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* structure containing information private to the storage module.
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* Each SwapDir has the concept of a maximum object size. This is used
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* as a basic hint to the storage layer in first choosing a suitable
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* SwapDir. The checkobj function is then called for suitable
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* candidate SwapDirs to find out whether it wants to store a
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* given StoreEntry. A maxobjsize of -1 means 'any size'.
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* The core API for storage modules this class provides all the hooks
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* squid uses to interact with a filesystem IO module.
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class StoreFileSystem
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static void RegisterAllFsWithCacheManager(CacheManager & manager);
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static void SetupAllFs();
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static void FsAdd(StoreFileSystem &);
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static void FreeAllFs();
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static Vector<StoreFileSystem*> const &FileSystems();
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typedef Vector<StoreFileSystem*>::iterator iterator;
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typedef Vector<StoreFileSystem*>::const_iterator const_iterator;
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StoreFileSystem() : initialised (false) {}
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StoreFileSystem() : initialised(false) {}
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virtual ~StoreFileSystem(){}
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virtual ~StoreFileSystem() {}
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virtual char const *type () const = 0;
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virtual SwapDir *createSwapDir() = 0;
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virtual void done() = 0;
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virtual void registerWithCacheManager(CacheManager & manager);
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virtual void setup() = 0;
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// Not implemented
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StoreFileSystem(StoreFileSystem const &);