OpenCores
URL https://opencores.org/ocsvn/openrisc/openrisc/trunk

Subversion Repositories openrisc

[/] [openrisc/] [trunk/] [rtos/] [ecos-2.0/] [doc/] [html/] [ref/] [fileio-file-table.html] - Blame information for rev 638

Go to most recent revision | Details | Compare with Previous | View Log

Line No. Rev Author Line
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 
>File 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="Mount Table"
26 
HREF="fileio-mount-table.html"><LINK
27 
REL="NEXT"
28 
TITLE="Directories"
29 
HREF="fileio-directories.html"></HEAD
30 
><BODY
31 
CLASS="CHAPTER"
32 
BGCOLOR="#FFFFFF"
33 
TEXT="#000000"
34 
LINK="#0000FF"
35 
VLINK="#840084"
36 
ALINK="#0000FF"
37 
><DIV
38 
CLASS="NAVHEADER"
39 
><TABLE
40 
SUMMARY="Header navigation table"
41 
WIDTH="100%"
42 
BORDER="0"
43 
CELLPADDING="0"
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-mount-table.html"
58 
ACCESSKEY="P"
59 
>Prev</A
60 
></TD
61 
><TD
62 
WIDTH="80%"
63 
ALIGN="center"
64 
VALIGN="bottom"
65 
></TD
66 
><TD
67 
WIDTH="10%"
68 
ALIGN="right"
69 
VALIGN="bottom"
70 
><A
71 
HREF="fileio-directories.html"
72 
ACCESSKEY="N"
73 
>Next</A
74 
></TD
75 
></TR
76 
></TABLE
77 
><HR
78 
ALIGN="LEFT"
79 
WIDTH="100%"></DIV
80 
><DIV
81 
CLASS="CHAPTER"
82 
><H1
83 
><A
84 
NAME="FILEIO-FILE-TABLE">Chapter 22. File Table</H1
85 
><P
86 
>Once a file has been opened it is represented by an open file
87 
object. These are allocated from an array of available file
88 
objects. User code accesses these open file objects via a second array
89 
of pointers which is indexed by small integer offsets. This gives the
90 
usual Unix file descriptor functionality, complete with the various
91 
duplication mechanisms.</P
92 
><P
93 
>A file table entry has the following structure:</P
94 
><TABLE
95 
BORDER="5"
96 
BGCOLOR="#E0E0F0"
97 
WIDTH="70%"
98 
><TR
99 
><TD
100 
><PRE
101 
CLASS="PROGRAMLISTING"
102 
>struct CYG_FILE_TAG
103 
{
104 
    cyg_uint32                  f_flag;         /* file state                   */
105 
    cyg_uint16                  f_ucount;       /* use count                    */
106 
    cyg_uint16                  f_type;         /* descriptor type              */
107 
    cyg_uint32                  f_syncmode;     /* synchronization protocol     */
108 
    struct CYG_FILEOPS_TAG      *f_ops;         /* file operations              */
109 
    off_t                       f_offset;       /* current offset               */
110 
    CYG_ADDRWORD                f_data;         /* file or socket               */
111 
    CYG_ADDRWORD                f_xops;         /* extra type specific ops      */
112 
    cyg_mtab_entry              *f_mte;         /* mount table entry            */
113 
};</PRE
114 
></TD
115 
></TR
116 
></TABLE
117 
><P
118 
>The <TT
119 
CLASS="STRUCTFIELD"
120 
><I
121 
>f_flag</I
122 
></TT
123 
> field contains some FILEIO
124 
control bits and some bits propagated from the
125 
<TT
126 
CLASS="PARAMETER"
127 
><I
128 
>flags</I
129 
></TT
130 
> argument of the
131 
<TT
132 
CLASS="FUNCTION"
133 
>open()</TT
134 
> call (defined by
135 
<TT
136 
CLASS="LITERAL"
137 
>CYG_FILE_MODE_MASK</TT
138 
>).</P
139 
><P
140 
>The <TT
141 
CLASS="STRUCTFIELD"
142 
><I
143 
>f_ucount</I
144 
></TT
145 
> field contains a use count that
146 
controls when a file will be closed. Each duplicate in the file
147 
descriptor array counts for one reference here. It is also
148 
incremented around each I/O operation to ensure that the file cannot
149 
be closed while it has current I/O operations.</P
150 
><P
151 
>The <TT
152 
CLASS="STRUCTFIELD"
153 
><I
154 
>f_type</I
155 
></TT
156 
> field indicates the type of the
157 
underlying file object. Some of the possible values here are
158 
<TT
159 
CLASS="LITERAL"
160 
>CYG_FILE_TYPE_FILE</TT
161 
>,
162 
<TT
163 
CLASS="LITERAL"
164 
>CYG_FILE_TYPE_SOCKET</TT
165 
> or <TT
166 
CLASS="LITERAL"
167 
>CYG_FILE_TYPE_DEVICE</TT
168 
>.</P
169 
><P
170 
>The <TT
171 
CLASS="STRUCTFIELD"
172 
><I
173 
>f_syncmode</I
174 
></TT
175 
> field is copied from the
176 
<TT
177 
CLASS="STRUCTFIELD"
178 
><I
179 
>syncmode</I
180 
></TT
181 
> field of the implementing
182 
filesystem. Its use is described in <A
183 
HREF="fileio-synchronization.html"
184 
>Chapter 24</A
185 
>.</P
186 
><P
187 
>The <TT
188 
CLASS="STRUCTFIELD"
189 
><I
190 
>f_offset</I
191 
></TT
192 
> field records the current file
193 
position. It is the responsibility of the file operation functions to
194 
keep this field up to date.</P
195 
><P
196 
>The <TT
197 
CLASS="STRUCTFIELD"
198 
><I
199 
>f_data</I
200 
></TT
201 
> field contains private data
202 
placed here by the underlying filesystem. Normally this will be a
203 
pointer to, or handle on, the filesystem object that implements this
204 
file.</P
205 
><P
206 
>The <TT
207 
CLASS="STRUCTFIELD"
208 
><I
209 
>f_xops</I
210 
></TT
211 
> field contains a pointer to any
212 
extra type specific operation functions. For example, the socket I/O
213 
system installs a pointer to a table of functions that implement the
214 
standard socket operations.</P
215 
><P
216 
>The <TT
217 
CLASS="STRUCTFIELD"
218 
><I
219 
>f_mte</I
220 
></TT
221 
> field contains a pointer to the
222 
parent mount table entry for this file. It is used mainly to implement
223 
the synchronization protocol. This may contain a pointer to some other
224 
data structure in file objects not derived from a filesystem.</P
225 
><P
226 
>The <TT
227 
CLASS="STRUCTFIELD"
228 
><I
229 
>f_ops</I
230 
></TT
231 
> field contains a pointer to a
232 
table of file I/O operations. This has the following structure:</P
233 
><TABLE
234 
BORDER="5"
235 
BGCOLOR="#E0E0F0"
236 
WIDTH="70%"
237 
><TR
238 
><TD
239 
><PRE
240 
CLASS="PROGRAMLISTING"
241 
>struct CYG_FILEOPS_TAG
242 
{
243 
        int     (*fo_read)      (struct CYG_FILE_TAG *fp, struct CYG_UIO_TAG *uio);
244 
        int     (*fo_write)     (struct CYG_FILE_TAG *fp, struct CYG_UIO_TAG *uio);
245 
        int     (*fo_lseek)     (struct CYG_FILE_TAG *fp, off_t *pos, int whence );
246 
        int     (*fo_ioctl)     (struct CYG_FILE_TAG *fp, CYG_ADDRWORD com,
247 
                                 CYG_ADDRWORD data);
248 
        int     (*fo_select)    (struct CYG_FILE_TAG *fp, int which, CYG_ADDRWORD info);
249 
        int     (*fo_fsync)     (struct CYG_FILE_TAG *fp, int mode );
250 
        int     (*fo_close)     (struct CYG_FILE_TAG *fp);
251 
        int     (*fo_fstat)     (struct CYG_FILE_TAG *fp, struct stat *buf );
252 
        int     (*fo_getinfo)   (struct CYG_FILE_TAG *fp, int key, char *buf, int len );
253 
        int     (*fo_setinfo)   (struct CYG_FILE_TAG *fp, int key, char *buf, int len );
254 
};</PRE
255 
></TD
256 
></TR
257 
></TABLE
258 
><P
259 
>It should be obvious from the names of most of these functions what
260 
their responsibilities are. The <TT
261 
CLASS="FUNCTION"
262 
>fo_getinfo()</TT
263 
>
264 
and <TT
265 
CLASS="FUNCTION"
266 
>fo_setinfo()</TT
267 
> function pointers, like their
268 
counterparts in the filesystem structure, implement minor control and
269 
info functions such as <TT
270 
CLASS="FUNCTION"
271 
>fpathconf()</TT
272 
>.</P
273 
><P
274 
>The second argument to the <TT
275 
CLASS="FUNCTION"
276 
>fo_read()</TT
277 
> and
278 
<TT
279 
CLASS="FUNCTION"
280 
>fo_write()</TT
281 
> function pointers is a pointer to a
282 
UIO structure:</P
283 
><TABLE
284 
BORDER="5"
285 
BGCOLOR="#E0E0F0"
286 
WIDTH="70%"
287 
><TR
288 
><TD
289 
><PRE
290 
CLASS="PROGRAMLISTING"
291 
>struct CYG_UIO_TAG
292 
{
293 
    struct CYG_IOVEC_TAG *uio_iov;      /* pointer to array of iovecs */
294 
    int                  uio_iovcnt;    /* number of iovecs in array */
295 
    off_t                uio_offset;    /* offset into file this uio corresponds to */
296 
    ssize_t              uio_resid;     /* residual i/o count */
297 
    enum cyg_uio_seg     uio_segflg;    /* see above */
298 
    enum cyg_uio_rw      uio_rw;        /* see above */
299 
};
300 
 
301 
struct CYG_IOVEC_TAG
302 
{
303 
    void           *iov_base;           /* Base address. */
304 
    ssize_t        iov_len;             /* Length. */
305 
};</PRE
306 
></TD
307 
></TR
308 
></TABLE
309 
><P
310 
>This structure encapsulates the parameters of any data transfer
311 
operation. It provides support for scatter/gather operations and
312 
records the progress of any data transfer. It is also compatible with
313 
the I/O operations of any BSD-derived network stacks and filesystems.</P
314 
><P
315 
>When a file is opened (or a file object created by some other means,
316 
such as <TT
317 
CLASS="FUNCTION"
318 
>socket()</TT
319 
> or <TT
320 
CLASS="FUNCTION"
321 
>accept()</TT
322 
>) it is the
323 
responsibility of the filesystem open operation to initialize all the
324 
fields of the object except the <TT
325 
CLASS="STRUCTFIELD"
326 
><I
327 
>f_ucount</I
328 
></TT
329 
>,
330 
<TT
331 
CLASS="STRUCTFIELD"
332 
><I
333 
>f_syncmode</I
334 
></TT
335 
> and
336 
<TT
337 
CLASS="STRUCTFIELD"
338 
><I
339 
>f_mte</I
340 
></TT
341 
> fields. Since the
342 
<TT
343 
CLASS="STRUCTFIELD"
344 
><I
345 
>f_flag</I
346 
></TT
347 
> field will already contain bits belonging to the FILEIO
348 
infrastructure, any changes to it must be made with the appropriate
349 
logical operations.</P
350 
></DIV
351 
><DIV
352 
CLASS="NAVFOOTER"
353 
><HR
354 
ALIGN="LEFT"
355 
WIDTH="100%"><TABLE
356 
SUMMARY="Footer navigation table"
357 
WIDTH="100%"
358 
BORDER="0"
359 
CELLPADDING="0"
360 
CELLSPACING="0"
361 
><TR
362 
><TD
363 
WIDTH="33%"
364 
ALIGN="left"
365 
VALIGN="top"
366 
><A
367 
HREF="fileio-mount-table.html"
368 
ACCESSKEY="P"
369 
>Prev</A
370 
></TD
371 
><TD
372 
WIDTH="34%"
373 
ALIGN="center"
374 
VALIGN="top"
375 
><A
376 
HREF="ecos-ref.html"
377 
ACCESSKEY="H"
378 
>Home</A
379 
></TD
380 
><TD
381 
WIDTH="33%"
382 
ALIGN="right"
383 
VALIGN="top"
384 
><A
385 
HREF="fileio-directories.html"
386 
ACCESSKEY="N"
387 
>Next</A
388 
></TD
389 
></TR
390 
><TR
391 
><TD
392 
WIDTH="33%"
393 
ALIGN="left"
394 
VALIGN="top"
395 
>Mount Table</TD
396 
><TD
397 
WIDTH="34%"
398 
ALIGN="center"
399 
VALIGN="top"
400 
><A
401 
HREF="fileio.html"
402 
ACCESSKEY="U"
403 
>Up</A
404 
></TD
405 
><TD
406 
WIDTH="33%"
407 
ALIGN="right"
408 
VALIGN="top"
409 
>Directories</TD
410 
></TR
411 
></TABLE
412 
></DIV
413 
></BODY
414 
></HTML
415 
>

powered by: WebSVN 2.1.0

© copyright 1999-2024 OpenCores.org, equivalent to Oliscience, all rights reserved. OpenCores®, registered trademark.