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<!-- Copyright (C) 2003 Red Hat, Inc.                                -->
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<!-- or later (the latest version is presently available at          -->
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><DIV
CLASS="CHAPTER"
><H1
><A
NAME="FILEIO-MOUNT-TABLE">Chapter 21. Mount Table</H1
><P
>The mount table records the filesystems that are actually active.
These can be seen as being analogous to mount points in Unix systems.</P
><P
>There are two sources of mount table entries. Filesystems (or other
components) may export static entries to the table using the
<TT
CLASS="LITERAL"
>MTAB_ENTRY()</TT
> macro. Alternatively, new entries may
be installed at run time using the <TT
CLASS="FUNCTION"
>mount()</TT
>
function. Both types of entry may be unmounted with the
<TT
CLASS="FUNCTION"
>umount()</TT
> function.</P
><P
>A mount table entry has the following structure:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>struct cyg_mtab_entry
{
    const char          *name;          // name of mount point
    const char          *fsname;        // name of implementing filesystem
    const char          *devname;       // name of hardware device
    CYG_ADDRWORD        data;           // private data value
    cyg_bool            valid;          // Valid entry?
    cyg_fstab_entry     *fs;            // pointer to fstab entry
    cyg_dir             root;           // root directory pointer
};</PRE
></TD
></TR
></TABLE
><P
>The <TT
CLASS="STRUCTFIELD"
><I
>name</I
></TT
> field identifies the mount
point. This is used to direct rooted filenames (filenames that
begin with &quot;/&quot;) to the correct filesystem. When a file
name that begins with &quot;/&quot; is submitted, it is matched
against the <TT
CLASS="STRUCTFIELD"
><I
>name</I
></TT
> fields of all valid mount
table entries. The entry that yields the longest match terminating
before a &quot;/&quot;, or end of string, wins and the appropriate
function from the filesystem table entry is then passed the remainder
of the file name together with a pointer to the table entry and the
value of the <TT
CLASS="STRUCTFIELD"
><I
>root</I
></TT
> field as the directory
pointer.</P
><P
>For example, consider a mount table that contains the following
entries:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>       { "/",    "msdos", "/dev/hd0", ... }
        { "/fd",  "msdos", "/dev/fd0", ... }
        { "/rom", "romfs", "", ... }
        { "/tmp", "ramfs", "", ... }
        { "/dev", "devfs", "", ... }</PRE
></TD
></TR
></TABLE
><P
>An attempt to open &quot;/tmp/foo&quot; would be directed to the RAM
filesystem while an open of &quot;/bar/bundy&quot; would be directed
to the hard disc MSDOS filesystem. Opening &quot;/dev/tty0&quot; would
be directed to the device management filesystem for lookup in the
device table.</P
><P
>Unrooted file names (those that do not begin with a '/') are passed
straight to the filesystem that contains the current directory. The
current directory is represented by a pair consisting of a mount table
entry and a directory pointer.</P
><P
>The <TT
CLASS="STRUCTFIELD"
><I
>fsname</I
></TT
> field points to a string that
should match the <TT
CLASS="STRUCTFIELD"
><I
>name</I
></TT
> field of the
implementing filesystem. During initialization the mount table is
scanned and the <TT
CLASS="STRUCTFIELD"
><I
>fsname</I
></TT
> entries looked up in
the filesystem table. For each match, the filesystem's _mount_
function is called and if successful the mount table entry is marked
as valid and the <TT
CLASS="STRUCTFIELD"
><I
>fs</I
></TT
> pointer installed.</P
><P
>The <TT
CLASS="STRUCTFIELD"
><I
>devname</I
></TT
> field contains the name of the
device that this filesystem is to use. This may match an entry in the
device table (see later) or may be a string that is specific to the
filesystem if it has its own internal device drivers.</P
><P
>The <TT
CLASS="STRUCTFIELD"
><I
>data</I
></TT
> field is a private data value. This
may be installed either statically when the table entry is defined, or
may be installed during the <TT
CLASS="FUNCTION"
>mount()</TT
> operation.</P
><P
>The <TT
CLASS="STRUCTFIELD"
><I
>valid</I
></TT
> field indicates whether this mount
point has actually been mounted successfully. Entries with a false
<TT
CLASS="STRUCTFIELD"
><I
>valid</I
></TT
> field are ignored when searching for a
name match.</P
><P
>The <TT
CLASS="STRUCTFIELD"
><I
>fs</I
></TT
> field is installed after a successful
<TT
CLASS="FUNCTION"
>mount()</TT
> operation to point to the implementing
filesystem.</P
><P
>The <TT
CLASS="STRUCTFIELD"
><I
>root</I
></TT
> field contains a directory pointer
value that the filesystem can interpret as the root of its directory
tree. This is passed as the <TT
CLASS="PARAMETER"
><I
>dir</I
></TT
> argument of
filesystem functions that operate on rooted filenames. This field must
be initialized by the filesystem's <TT
CLASS="FUNCTION"
>mount()</TT
>
function.</P
></DIV
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>

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1	28	unneback	`<!-- Copyright (C) 2003 Red Hat, Inc. -->`
2			`<!-- This material may be distributed only subject to the terms -->`
3			`<!-- and conditions set forth in the Open Publication License, v1.0 -->`
4			`<!-- or later (the latest version is presently available at -->`
5			`<!-- http://www.opencontent.org/openpub/). -->`
6			`<!-- Distribution of the work or derivative of the work in any -->`
7			`<!-- standard (paper) book form is prohibited unless prior -->`
8			`<!-- permission is obtained from the copyright holder. -->`
9			`<HTML`
10			`><HEAD`
11			`><TITLE`
12			`>Mount Table</TITLE`
13			`><meta name="MSSmartTagsPreventParsing" content="TRUE">`
14			`<META`
15			`NAME="GENERATOR"`
16			`CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+`
17			`"><LINK`
18			`REL="HOME"`
19			`TITLE="eCos Reference Manual"`
20			`HREF="ecos-ref.html"><LINK`
21			`REL="UP"`
22			`TITLE="File System Support Infrastructure"`
23			`HREF="fileio.html"><LINK`
24			`REL="PREVIOUS"`
25			`TITLE="File System Table"`
26			`HREF="fileio-fstab.html"><LINK`
27			`REL="NEXT"`
28			`TITLE="File Table"`
29			`HREF="fileio-file-table.html"></HEAD`
30			`><BODY`
31			`CLASS="CHAPTER"`
32			`BGCOLOR="#FFFFFF"`
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34			`LINK="#0000FF"`
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39			`><TABLE`
40			`SUMMARY="Header navigation table"`
41			`WIDTH="100%"`
42			`BORDER="0"`
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44			`CELLSPACING="0"`
45			`><TR`
46			`><TH`
47			`COLSPAN="3"`
48			`ALIGN="center"`
49			`>eCos Reference Manual</TH`
50			`></TR`
51			`><TR`
52			`><TD`
53			`WIDTH="10%"`
54			`ALIGN="left"`
55			`VALIGN="bottom"`
56			`><A`
57			`HREF="fileio-fstab.html"`
58			`ACCESSKEY="P"`
59			`>Prev</A`
60			`></TD`
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63			`ALIGN="center"`
64			`VALIGN="bottom"`
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66			`><TD`
67			`WIDTH="10%"`
68			`ALIGN="right"`
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70			`><A`
71			`HREF="fileio-file-table.html"`
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73			`>Next</A`
74			`></TD`
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76			`></TABLE`
77			`><HR`
78			`ALIGN="LEFT"`
79			`WIDTH="100%"></DIV`
80			`><DIV`
81			`CLASS="CHAPTER"`
82			`><H1`
83			`><A`
84			`NAME="FILEIO-MOUNT-TABLE">Chapter 21. Mount Table</H1`
85			`><P`
86			`>The mount table records the filesystems that are actually active.`
87			`These can be seen as being analogous to mount points in Unix systems.</P`
88			`><P`
89			`>There are two sources of mount table entries. Filesystems (or other`
90			`components) may export static entries to the table using the`
91			`<TT`
92			`CLASS="LITERAL"`
93			`>MTAB_ENTRY()</TT`
94			`> macro. Alternatively, new entries may`
95			`be installed at run time using the <TT`
96			`CLASS="FUNCTION"`
97			`>mount()</TT`
98			`>`
99			`function. Both types of entry may be unmounted with the`
100			`<TT`
101			`CLASS="FUNCTION"`
102			`>umount()</TT`
103			`> function.</P`
104			`><P`
105			`>A mount table entry has the following structure:</P`
106			`><TABLE`
107			`BORDER="5"`
108			`BGCOLOR="#E0E0F0"`
109			`WIDTH="70%"`
110			`><TR`
111			`><TD`
112			`><PRE`
113			`CLASS="PROGRAMLISTING"`
114			`>struct cyg_mtab_entry`
115			`{`
116			`const char *name; // name of mount point`
117			`const char *fsname; // name of implementing filesystem`
118			`const char *devname; // name of hardware device`
119			`CYG_ADDRWORD data; // private data value`
120			`cyg_bool valid; // Valid entry?`
121			`cyg_fstab_entry *fs; // pointer to fstab entry`
122			`cyg_dir root; // root directory pointer`
123			`};</PRE`
124			`></TD`
125			`></TR`
126			`></TABLE`
127			`><P`
128			`>The <TT`
129			`CLASS="STRUCTFIELD"`
130			`><I`
131			`>name</I`
132			`></TT`
133			`> field identifies the mount`
134			`point. This is used to direct rooted filenames (filenames that`
135			`begin with "/") to the correct filesystem. When a file`
136			`name that begins with "/" is submitted, it is matched`
137			`against the <TT`
138			`CLASS="STRUCTFIELD"`
139			`><I`
140			`>name</I`
141			`></TT`
142			`> fields of all valid mount`
143			`table entries. The entry that yields the longest match terminating`
144			`before a "/", or end of string, wins and the appropriate`
145			`function from the filesystem table entry is then passed the remainder`
146			`of the file name together with a pointer to the table entry and the`
147			`value of the <TT`
148			`CLASS="STRUCTFIELD"`
149			`><I`
150			`>root</I`
151			`></TT`
152			`> field as the directory`
153			`pointer.</P`
154			`><P`
155			`>For example, consider a mount table that contains the following`
156			`entries:</P`
157			`><TABLE`
158			`BORDER="5"`
159			`BGCOLOR="#E0E0F0"`
160			`WIDTH="70%"`
161			`><TR`
162			`><TD`
163			`><PRE`
164			`CLASS="PROGRAMLISTING"`
165			`> { "/", "msdos", "/dev/hd0", ... }`
166			`{ "/fd", "msdos", "/dev/fd0", ... }`
167			`{ "/rom", "romfs", "", ... }`
168			`{ "/tmp", "ramfs", "", ... }`
169			`{ "/dev", "devfs", "", ... }</PRE`
170			`></TD`
171			`></TR`
172			`></TABLE`
173			`><P`
174			`>An attempt to open "/tmp/foo" would be directed to the RAM`
175			`filesystem while an open of "/bar/bundy" would be directed`
176			`to the hard disc MSDOS filesystem. Opening "/dev/tty0" would`
177			`be directed to the device management filesystem for lookup in the`
178			`device table.</P`
179			`><P`
180			`>Unrooted file names (those that do not begin with a '/') are passed`
181			`straight to the filesystem that contains the current directory. The`
182			`current directory is represented by a pair consisting of a mount table`
183			`entry and a directory pointer.</P`
184			`><P`
185			`>The <TT`
186			`CLASS="STRUCTFIELD"`
187			`><I`
188			`>fsname</I`
189			`></TT`
190			`> field points to a string that`
191			`should match the <TT`
192			`CLASS="STRUCTFIELD"`
193			`><I`
194			`>name</I`
195			`></TT`
196			`> field of the`
197			`implementing filesystem. During initialization the mount table is`
198			`scanned and the <TT`
199			`CLASS="STRUCTFIELD"`
200			`><I`
201			`>fsname</I`
202			`></TT`
203			`> entries looked up in`
204			`the filesystem table. For each match, the filesystem's _mount_`
205			`function is called and if successful the mount table entry is marked`
206			`as valid and the <TT`
207			`CLASS="STRUCTFIELD"`
208			`><I`
209			`>fs</I`
210			`></TT`
211			`> pointer installed.</P`
212			`><P`
213			`>The <TT`
214			`CLASS="STRUCTFIELD"`
215			`><I`
216			`>devname</I`
217			`></TT`
218			`> field contains the name of the`
219			`device that this filesystem is to use. This may match an entry in the`
220			`device table (see later) or may be a string that is specific to the`
221			`filesystem if it has its own internal device drivers.</P`
222			`><P`
223			`>The <TT`
224			`CLASS="STRUCTFIELD"`
225			`><I`
226			`>data</I`
227			`></TT`
228			`> field is a private data value. This`
229			`may be installed either statically when the table entry is defined, or`
230			`may be installed during the <TT`
231			`CLASS="FUNCTION"`
232			`>mount()</TT`
233			`> operation.</P`
234			`><P`
235			`>The <TT`
236			`CLASS="STRUCTFIELD"`
237			`><I`
238			`>valid</I`
239			`></TT`
240			`> field indicates whether this mount`
241			`point has actually been mounted successfully. Entries with a false`
242			`<TT`
243			`CLASS="STRUCTFIELD"`
244			`><I`
245			`>valid</I`
246			`></TT`
247			`> field are ignored when searching for a`
248			`name match.</P`
249			`><P`
250			`>The <TT`
251			`CLASS="STRUCTFIELD"`
252			`><I`
253			`>fs</I`
254			`></TT`
255			`> field is installed after a successful`
256			`<TT`
257			`CLASS="FUNCTION"`
258			`>mount()</TT`
259			`> operation to point to the implementing`
260			`filesystem.</P`
261			`><P`
262			`>The <TT`
263			`CLASS="STRUCTFIELD"`
264			`><I`
265			`>root</I`
266			`></TT`
267			`> field contains a directory pointer`
268			`value that the filesystem can interpret as the root of its directory`
269			`tree. This is passed as the <TT`
270			`CLASS="PARAMETER"`
271			`><I`
272			`>dir</I`
273			`></TT`
274			`> argument of`
275			`filesystem functions that operate on rooted filenames. This field must`
276			`be initialized by the filesystem's <TT`
277			`CLASS="FUNCTION"`
278			`>mount()</TT`
279			`>`
280			`function.</P`
281			`></DIV`
282			`><DIV`
283			`CLASS="NAVFOOTER"`
284			`><HR`
285			`ALIGN="LEFT"`
286			`WIDTH="100%"><TABLE`
287			`SUMMARY="Footer navigation table"`
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324			`ALIGN="left"`
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326			`>File System Table</TD`
327			`><TD`
328			`WIDTH="34%"`
329			`ALIGN="center"`
330			`VALIGN="top"`
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332			`HREF="fileio.html"`
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334			`>Up</A`
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346			`>`

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