2 # Captive project doc Cache Manager page Perl template.
3 # Copyright (C) 2003-2005 Jan Kratochvil <project-www.jankratochvil.net@jankratochvil.net>
5 # This program is free software; you can redistribute it and/or modify
6 # it under the terms of the GNU General Public License as published by
7 # the Free Software Foundation; exactly version 2 of June 1991 is required
9 # This program is distributed in the hope that it will be useful,
10 # but WITHOUT ANY WARRANTY; without even the implied warranty of
11 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 # GNU General Public License for more details.
14 # You should have received a copy of the GNU General Public License
15 # along with this program; if not, write to the Free Software
16 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
19 package project::captive::doc::CacheManager;
20 require 5.6.0; # at least 'use warnings;' but we need some 5.6.0+ modules anyway
21 our $VERSION=do { my @r=(q$Revision$=~/\d+/g); sprintf "%d.".("%03d"x$#r),@r; };
32 BEGIN { Wuse 'project::captive::doc::Macros'; }
33 project::captive::doc::Macros->init(
34 "title"=>'Captive NTFS Developer Documentation: NT Cache Manager',
35 "rel_prev"=>'Reverse.pm',
36 "rel_next"=>'Details.pm',
43 <h1 id="cache_manager">NT Cache Manager</h1>
45 <p>Although there exist some 3rd party documents about
46 <span class="productname">NT Cache Manager</span> W32 subsystem such as
47 <span class="productname">@{[ a_href 'http://www.osr.com/ntinsider/1996/cacheman.htm',
48 'The NT Cache Manager Description' ]}</span> or
49 <span class="productname">@{[ a_href 'http://www.winntmag.com/Articles/Print.cfm?ArticleID=3864',
50 'Learn About NT'."'".'s File-system Cache' ]}</span>
51 they are definitely insufficient for compatible
52 <span class="productname">NT Cache Manager</span> reimplementation.</p>
54 <p><span class="productname">NT Cache Manager</span> is about mapping
55 filesystem objects such as regular file data, filesystem bitmap or
56 journalling zone (log file). It is also being used by the filesystem for
57 mapping of virtual volume files representing the whole underlying
58 filesystem device.</p>
60 <p>The original W32 <span class="productname">NT Cache Manager</span>
61 is much more complicated as it must coordinate its effort with
62 other W32 subsystems like mapping of executable files
63 (<span class="type">ImageSectionObject</span>), insufficient system
64 resources from <span class="productname">NT Memory Manager</span>
65 or general effort to perform caching features for system performance.</p>
66 <p><span class="productname">NT Cache Manager</span> of this project has much
67 simpler goal - it just needs to provide compatible
68 <span class="productname">NT Cache Manager</span> functionality while
69 the other goals of its W32 counterpart are left to be successfuly handled
70 by UNIX OS in much more efficient way.</p>
72 @{[ doc_img 'dia/cache-manager',
73 '<span class="productname">NT Cache Manager</span> Architecture' ]}
75 <p>Cache Manager objects are always bound to
76 <span class="type">FCB</span> (File Control Block).
77 <span class="type">FileObject</span> (or its associated
78 <span class="type">HANDLE</span>) serve only as reference
79 to <span class="type">FCB</span> and there can be multiple
80 <span class="type">FileObject</span>/<span class="type">HANDLE</span>
81 items for one <span class="type">FCB</span>. It is a bit misleading
82 you must use <span class="type">FileObject</span> pointer while calling
83 most of the Cache Manager functions.</p>
85 <p>Before using any other Cache Manager functions you must first call
86 <span class="function">CcInitializeCacheMap()</span>. You must give the
87 maximum mapped object offset. Each mapped object byte must have at most one
88 mapped memory location - no shared pages are allowed. Also any subsequent
89 mapping request is expected to be mapped into continuous memory region.
90 It implies you must reserve the memory region for possible future mapping
91 during the initial <span class="function">CcInitializeCacheMap()</span>
92 moment sized according to the given maximum mapped object offset.
93 This is the approach currently implemented by this project although it
94 cannot be used for 3rd party <span class="fname">ext2fsd.sys</span>
95 driver as it initialized Cache Manager by the whole media device size
96 and it surprisingly succeeds for original
97 <span class="productname">Microsoft Windows</span>
98 <span class="productname">Cache Manager</span>.
99 I expect the space reservation should be postponed to the first mapping
100 request and expect no multiple mappings will be done in the case
101 of memory-exceeding <span class="function">CcInitializeCacheMap()</span>
102 reservation request. <span class="function">CcSetFileSizes()</span>
103 changing the reserved memory area size may assume no existing Map
104 or Pin mappings exist. Only in the case of
105 <span class="constant">FO_STREAM_FILE</span> (virtual device file)
106 it is permitted to extend mapped size even in the case of existing
107 (and dirty) Map or Pin mappings.</p>
109 <p><span class="type">PCACHE_MANAGER_CALLBACKS</span> argument can be
113 <dt><span class="function">AcquireForReadAhead()</span>/<span class="function">ReleaseFromReadAhead()</span></dt>
115 <p>As any readahead functionality is optional these entries are
116 never used by Cache Manager implementation of this project.</p>
119 <dt><span class="function">AcquireForLazyWrite()</span>/<span class="function">ReleaseFromLazyWrite()</span></dt>
121 <p>Even the write-behind functionality is optional for Cache Manager.
122 It is being done in asynchronous way in the original
123 <span class="productname">Microsoft Windows</span>
124 <span class="productname">Cache Manager</span>.
125 implementation and it is ignored by Cache Manager implementation of
128 <p>Cache Manager does not need to write any data if not explicitely
129 requested by the driver. It is even expected to silently drop any
130 pending dirty data blocks during filesystem shutdown.
131 Forced dirty block write by function
132 <span class="function">CcFlushCache()</span> should be written without
133 any wrapping surrounding
134 <span class="function">AcquireForLazyWrite()</span>/<span class="function">ReleaseFromLazyWrite()</span>
139 <p><span class="function">CcUninitializeCacheMap()</span> is just
140 a suggestion for Cache Manager that driver will no longer reference
141 given <span class="type">SharedCacheMap</span>. The uninitialization
142 can be postponed to any later moment in original
143 <span class="productname">Microsoft Windows</span>
144 <span class="productname">Cache Manager</span>
145 as it may be locked by existing
146 <span class="type">ImageSectionObject</span>
147 of some file being executed etc.
148 <span id="sharedcachemap_leak">It is fatal to destroy
149 <span class="type">SharedCacheMap</span></span>
150 in the moment you see no other
151 references to it as the driver will access it for some moment
152 even after <span class="function">CcUninitializeCacheMap()</span>.
153 I am not sure if it is a bug of the driver or whether there are some rules
154 how long after <span class="function">CcUninitializeCacheMap()</span>
155 completion given <span class="type">SharedCacheMap</span> still exists.
156 Fortunately it is safe to never destroy
157 <span class="type">SharedCacheMap</span> and leave it leaked - everything
159 @{[ a_href 'Details.pm#sandbox','sandboxed environment' ]} soon anyway.</p>
161 <p>There exist Map and Pin type objects for each
162 <span class="type">SharedCacheMap</span> although they look very similiar.
163 Only these objects give you access to any memory data
164 — <span class="type">SharedCacheMap</span> only reserved the space
165 to ensure continuous mapping of the forthcoming mappings but it did not map
166 any data into it.</p>
168 <p>Mapping of 'new' Map or Pin will create the new object only in the case
169 no such mapping exists now. Otherwise you will just get the reference to
170 the existing object with increased usecount.</p>
175 <p>Map mapping is always at most one for each
176 <span class="type">SharedCacheMap</span>. Base offset/length of such
177 mapping have no meaning as there can be only single Map.</p>
179 <p>Apparently Map size can be arbitrary long according
180 to its <span class="type">SharedCacheMap</span> reserved space.</p>
182 <p>You cannot modify the memory mapped by Map in any way.
183 As it is the same memory area (address) as the pages used by Pin
184 objects you always access the last modified version by possible
185 Pin of the same page.</p>
190 <p>Pin mapping always represents just one physical page
191 (<span class="constant">PAGE_SIZE</span> – 4096 for i386).
192 Its base offset/length can be safely extended to be aligned to the
195 <p>Pin can have associated pair of oldest and newest
196 <span class="type">LSN</span> (Linear Sequence Number). It can be
197 set by <span class="function">CcSetDirtyPinnedData()</span>
198 and Cache Manager always tracks the lowest and highest
199 reported <span class="type">LSN</span> for each page.
200 <span class="type">LSN</span> is assumed to be
201 <span class="constant">0</span> if not set.</p>
203 <p>Any existing Pin mapping will be reused for further mappings
204 as long as it is not ThreadOwned. In the moment you use
205 <span class="function">CcSetBcbOwnerPointer()</span> you will detach
206 the associated Pin pages from its
207 <span class="type">SharedCacheMap</span>.
208 Although they will further act as valid Pin mappings they will be no
209 longer reused during new Pin mapping of the same page.
210 There can exist multiple Pin mappings of the same page (although
211 sharing the same memory space). This detaching must be implemented
213 @{[ a_href 'Details.pm#synchronous','single-threaded' ]} W32 implementation
214 of this project as it is affecting the behaviour of Cache Manager.
216 @{[ a_href 'CacheManager.pm#TraceFS','seen' ]} how to behave if multiple dirty Pin
217 mappings of the same page exist.</p>
221 <p>Only the pages not yet present in the memory must be read from the disk.
222 You must not read any pages you do not need to as the driver does not
223 expect it and it would corrupt its data buffers. There is just a strict
224 difference between <span class="function">CcPinRead()</span> and
225 <span class="function">CcPinMappedData()</span> function calls where
226 <span class="function">CcPinRead()</span> is required to re-read its data
227 blocks even if they were currently already Map mapped (unless it was already
228 also Pin mapped at least once). On the opposite side
229 <span class="function">CcPinMappedData()</span> must not re-read the given
230 blocks, moreover it blocks are required to be already Map mapped by the caller.</p>
232 <p>Cache Manager of this project will destroy Pin or Map mappings after
233 their last unreferencing (in opposite of
234 @{[ a_href '#sharedcachemap_leak','leaked <span class="type">SharedCacheMap</span>' ]}).
235 Despite it any dirty pages may still be held as the pages
236 (including their <span class="type">LSN</span>s) are cached associated
237 with <span class="type">SharedCacheMap</span>. It may be also possible
238 original <span class="productname">Microsoft Windows</span>
239 <span class="productname">Cache Manager</span>
240 postpones Pin mapping destroy to later time but it does not matter.</p>
243 <h2 id="TraceFS">TraceFS NT Cache Manager Tracer</h2>
245 <p>@{[ a_href '#cache_manager','Cache Manager behaviour' ]} would be hard
246 to analyze just by @{[ a_href '#reverse','reverse engineering' ]} as it
247 is pretty complicated code cooperating with many other W32 kernel
248 subsystems. It was chosen as easier way to trace it instead and validate
249 all the Cache Manager assumptions by Cache Manager simulator.</p>
251 @{[ doc_img 'dia/TraceFS','TraceFS Hooking' ]}
253 <p>You must prepare your driver to be hooked
254 (<span class="fname">ntfs.sys</span> in this case):</p>
256 <blockquote class="command">
257 <p>@{[ captive_srcfile './src/TraceFS/hookfs.pl' ]} ntfs.sys ./src/TraceFS/TraceFS-W32/TraceFS.sys >hooked/ntfs.sys</p>
260 <p>This <span class="fname">hooked/ntfs.sys</span> file must be replaced
261 in the <span class="fname">%System32%\\drivers</span> directory.
263 <span class="productname">Microsoft Windows</span>
264 has many backups of these system files such as
265 <span class="fname">%System32%\\dllcache</span> — delete them
268 <p>You also need to install
269 <span class="fname">./src/TraceFS/TraceFS-W32/TraceFS.sys</span>
270 into <span class="fname">%System32%\\drivers</span> directory
271 and import <span class="fname">TraceFS/TraceFS-W32/TraceFS.reg</span>
272 registry file to initialize the debug driver during system boot.</p>
274 <p>You can now pray a bit and snap the resulting Cache Manager tracing
275 from <span class="productname">WinDbg</span> by
276 @{[ a_href 'Reverse.pm#WinDbg','W32 remote kernel debugging' ]}:</p>
278 @{[ doc_img 'ntdebug-windbg-boot','Successfuly connected <span class="productname">WinDbg</span>' ]}
280 <p>The resulting trace file should be processed by
281 @{[ captive_srcfile './src/TraceFS/checktrace.pl' ]} Perl Cache Manager
282 implementation to validate its assumptions about Cache Manager behaviour.
283 Any seen incompatibilies will be reported — your target is to reach
284 as few error messages as possible.</p>
286 <p>KNOWN BUGS: Combination of message synchronization primitives and
287 implemented refusal to create journalling thread of
288 <span class="fname">ntfs.sys</span>
289 causes fatal system lockup in several advanced operations
290 such as setting compression attribute. Despite it more common operations
291 can be successfuly traced during the whole
292 <span class="productname">Microsoft Windows</span>
293 session including its final shutdown and such traces provide enough
294 material to be food to
295 @{[ captive_srcfile './src/TraceFS/checktrace.pl' ]} Perl Cache Manager
298 <h3 id="TraceFS_general">TraceFS for general API tracing</h3>
300 <p>Although TraceFS was up to now used only for tracing of
301 <span class="productname">NT Cache Manager</span> it can be easily
302 used ever for any other NT kernel API tracing. You need to provide
303 appropriate function wrappers in the main source file
304 @{[ captive_srcfile './src/TraceFS/TraceFS-W32/TraceFS.c' ]}.
305 Original system functions being wrapped should be called with their
306 original name. Your wrapping functions should have the first letter
307 of their name replaced by character
308 <span class="command">'T'</span>. Therefore wrapping of
309 <span class="function">CcInitializeCacheMap()</span> must be
310 done by your function
311 <span class="function">TcInitializeCacheMap()</span>.
312 Prototypes of both the wrapping and wrapped functions must be the same.
313 You must also export all the wrapped functions by
314 @{[ captive_srcfile './src/TraceFS/TraceFS-W32/TraceFS.def' ]}.
315 @{[ captive_srcfile './src/TraceFS/hookfs.pl' ]} has no hardcoded
316 function names – it will hook exactly the exported entries.</p>
318 <p>Framework for thread synchronizations and debug tracing is provided to
319 prevent mangling of messages while running by multiple threads at once.
320 Testing was done just on uniprocessor machine, SMP kernel may need some
327 project::captive::doc::Macros->footer();