fileio.c revision f12e285ffd9ff0b37c4f91d5ab2b021ed1eb43be 
1/*
2 * fileio.c --- Simple file I/O routines
3 *
4 * Copyright (C) 1997 Theodore Ts'o.
5 *
6 * %Begin-Header%
7 * This file may be redistributed under the terms of the GNU Public
8 * License.
9 * %End-Header%
10 */
11
12#include <stdio.h>
13#include <string.h>
14#if HAVE_UNISTD_H
15#include <unistd.h>
16#endif
17
18#include "ext2_fs.h"
19#include "ext2fs.h"
20
21struct ext2_file {
22	errcode_t		magic;
23	ext2_filsys 		fs;
24	ext2_ino_t		ino;
25	struct ext2_inode	inode;
26	int 			flags;
27	ext2_off_t		pos;
28	blk_t			blockno;
29	blk_t			physblock;
30	char 			*buf;
31};
32
33#define BMAP_BUFFER (file->buf + fs->blocksize)
34
35errcode_t ext2fs_file_open(ext2_filsys fs, ext2_ino_t ino,
36			   int flags, ext2_file_t *ret)
37{
38	ext2_file_t 	file;
39	errcode_t	retval;
40
41	/*
42	 * Don't let caller create or open a file for writing if the
43	 * filesystem is read-only.
44	 */
45	if ((flags & (EXT2_FILE_WRITE | EXT2_FILE_CREATE)) &&
46	    !(fs->flags & EXT2_FLAG_RW))
47		return EXT2_ET_RO_FILSYS;
48
49	retval = ext2fs_get_mem(sizeof(struct ext2_file), (void **) &file);
50	if (retval)
51		return retval;
52
53	memset(file, 0, sizeof(struct ext2_file));
54	file->magic = EXT2_ET_MAGIC_EXT2_FILE;
55	file->fs = fs;
56	file->ino = ino;
57	file->flags = flags & EXT2_FILE_MASK;
58
59	retval = ext2fs_read_inode(fs, ino, &file->inode);
60	if (retval)
61		goto fail;
62
63	retval = ext2fs_get_mem(fs->blocksize * 3, (void **) &file->buf);
64	if (retval)
65		goto fail;
66
67	*ret = file;
68	return 0;
69
70fail:
71	if (file->buf)
72		ext2fs_free_mem((void **) &file->buf);
73	ext2fs_free_mem((void **) &file);
74	return retval;
75}
76
77/*
78 * This function returns the filesystem handle of a file from the structure
79 */
80ext2_filsys ext2fs_file_get_fs(ext2_file_t file)
81{
82	if (file->magic != EXT2_ET_MAGIC_EXT2_FILE)
83		return 0;
84	return file->fs;
85}
86
87/*
88 * This function flushes the dirty block buffer out to disk if
89 * necessary.
90 */
91errcode_t ext2fs_file_flush(ext2_file_t file)
92{
93	errcode_t	retval;
94	ext2_filsys fs;
95
96	EXT2_CHECK_MAGIC(file, EXT2_ET_MAGIC_EXT2_FILE);
97	fs = file->fs;
98
99	if (!(file->flags & EXT2_FILE_BUF_VALID) ||
100	    !(file->flags & EXT2_FILE_BUF_DIRTY))
101		return 0;
102
103	/*
104	 * OK, the physical block hasn't been allocated yet.
105	 * Allocate it.
106	 */
107	if (!file->physblock) {
108		retval = ext2fs_bmap(fs, file->ino, &file->inode,
109				     BMAP_BUFFER, BMAP_ALLOC,
110				     file->blockno, &file->physblock);
111		if (retval)
112			return retval;
113	}
114
115	retval = io_channel_write_blk(fs->io, file->physblock,
116				      1, file->buf);
117	if (retval)
118		return retval;
119
120	file->flags &= ~EXT2_FILE_BUF_DIRTY;
121
122	return retval;
123}
124
125/*
126 * This function synchronizes the file's block buffer and the current
127 * file position, possibly invalidating block buffer if necessary
128 */
129static errcode_t sync_buffer_position(ext2_file_t file)
130{
131	blk_t	b;
132	errcode_t	retval;
133
134	b = file->pos / file->fs->blocksize;
135	if (b != file->blockno) {
136		retval = ext2fs_file_flush(file);
137		if (retval)
138			return retval;
139		file->flags &= ~EXT2_FILE_BUF_VALID;
140	}
141	file->blockno = b;
142	return 0;
143}
144
145/*
146 * This function loads the file's block buffer with valid data from
147 * the disk as necessary.
148 *
149 * If dontfill is true, then skip initializing the buffer since we're
150 * going to be replacing its entire contents anyway.  If set, then the
151 * function basically only sets file->physblock and EXT2_FILE_BUF_VALID
152 */
153#define DONTFILL 1
154static errcode_t load_buffer(ext2_file_t file, int dontfill)
155{
156	ext2_filsys	fs = file->fs;
157	errcode_t	retval;
158
159	if (!(file->flags & EXT2_FILE_BUF_VALID)) {
160		retval = ext2fs_bmap(fs, file->ino, &file->inode,
161				     BMAP_BUFFER, 0, file->blockno,
162				     &file->physblock);
163		if (retval)
164			return retval;
165		if (!dontfill) {
166			if (file->physblock) {
167				retval = io_channel_read_blk(fs->io,
168							     file->physblock,
169							     1, file->buf);
170				if (retval)
171					return retval;
172			} else
173				memset(file->buf, 0, fs->blocksize);
174		}
175		file->flags |= EXT2_FILE_BUF_VALID;
176	}
177	return 0;
178}
179
180
181errcode_t ext2fs_file_close(ext2_file_t file)
182{
183	errcode_t	retval;
184
185	EXT2_CHECK_MAGIC(file, EXT2_ET_MAGIC_EXT2_FILE);
186
187	retval = ext2fs_file_flush(file);
188
189	if (file->buf)
190		ext2fs_free_mem((void **) &file->buf);
191	ext2fs_free_mem((void **) &file);
192
193	return retval;
194}
195
196
197errcode_t ext2fs_file_read(ext2_file_t file, void *buf,
198			   unsigned int wanted, unsigned int *got)
199{
200	ext2_filsys	fs;
201	errcode_t	retval = 0;
202	unsigned int	start, left, c, count = 0;
203	char		*ptr = (char *) buf;
204
205	EXT2_CHECK_MAGIC(file, EXT2_ET_MAGIC_EXT2_FILE);
206	fs = file->fs;
207
208	while ((file->pos < file->inode.i_size) && (wanted > 0)) {
209		retval = sync_buffer_position(file);
210		if (retval)
211			goto fail;
212		retval = load_buffer(file, 0);
213		if (retval)
214			goto fail;
215
216		start = file->pos % fs->blocksize;
217		c = fs->blocksize - start;
218		if (c > wanted)
219			c = wanted;
220		left = file->inode.i_size - file->pos ;
221		if (c > left)
222			c = left;
223
224		memcpy(ptr, file->buf+start, c);
225		file->pos += c;
226		ptr += c;
227		count += c;
228		wanted -= c;
229	}
230
231fail:
232	if (got)
233		*got = count;
234	return retval;
235}
236
237
238errcode_t ext2fs_file_write(ext2_file_t file, const void *buf,
239			    unsigned int nbytes, unsigned int *written)
240{
241	ext2_filsys	fs;
242	errcode_t	retval = 0;
243	unsigned int	start, c, count = 0;
244	char		*ptr = (char *) buf;
245
246	EXT2_CHECK_MAGIC(file, EXT2_ET_MAGIC_EXT2_FILE);
247	fs = file->fs;
248
249	if (!(file->flags & EXT2_FILE_WRITE))
250		return EXT2_ET_FILE_RO;
251
252	while (nbytes > 0) {
253		retval = sync_buffer_position(file);
254		if (retval)
255			goto fail;
256
257		start = file->pos % fs->blocksize;
258		c = fs->blocksize - start;
259		if (c > nbytes)
260			c = nbytes;
261
262		/*
263		 * We only need to do a read-modify-update cycle if
264		 * we're doing a partial write.
265		 */
266		retval = load_buffer(file, (c == fs->blocksize));
267		if (retval)
268			goto fail;
269
270		file->flags |= EXT2_FILE_BUF_DIRTY;
271		memcpy(file->buf+start, ptr, c);
272		file->pos += c;
273		ptr += c;
274		count += c;
275		nbytes -= c;
276	}
277
278fail:
279	if (written)
280		*written = count;
281	return retval;
282}
283
284errcode_t ext2fs_file_lseek(ext2_file_t file, ext2_off_t offset,
285			    int whence, ext2_off_t *ret_pos)
286{
287	EXT2_CHECK_MAGIC(file, EXT2_ET_MAGIC_EXT2_FILE);
288
289	if (whence == EXT2_SEEK_SET)
290		file->pos = offset;
291	else if (whence == EXT2_SEEK_CUR)
292		file->pos += offset;
293	else if (whence == EXT2_SEEK_END)
294		file->pos = file->inode.i_size + offset;
295	else
296		return EXT2_ET_INVALID_ARGUMENT;
297
298	if (ret_pos)
299		*ret_pos = file->pos;
300
301	return 0;
302}
303
304/*
305 * This function returns the size of the file, according to the inode
306 */
307ext2_off_t ext2fs_file_get_size(ext2_file_t file)
308{
309	if (file->magic != EXT2_ET_MAGIC_EXT2_FILE)
310		return 0;
311	return file->inode.i_size;
312}
313
314/*
315 * This function sets the size of the file, truncating it if necessary
316 *
317 * XXX still need to call truncate
318 */
319errcode_t ext2fs_file_set_size(ext2_file_t file, ext2_off_t size)
320{
321	errcode_t	retval;
322	EXT2_CHECK_MAGIC(file, EXT2_ET_MAGIC_EXT2_FILE);
323
324	file->inode.i_size = size;
325	retval = ext2fs_write_inode(file->fs, file->ino, &file->inode);
326	if (retval)
327		return retval;
328
329	/*
330	 * XXX truncate inode if necessary
331	 */
332
333	return 0;
334}
335