summaryrefslogtreecommitdiffstats
path: root/arch/um/drivers/cow_user.c
blob: 93f227a25ba42f5742d1343c1fc7e0bb34a9ea74 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
/*
 * Copyright (C) 2007 Jeff Dike (jdike@{linux.intel,addtoit}.com)
 * Licensed under the GPL
 */

/*
 * _XOPEN_SOURCE is needed for pread, but we define _GNU_SOURCE, which defines
 * that.
 */
#include <unistd.h>
#include <byteswap.h>
#include <errno.h>
#include <string.h>
#include <arpa/inet.h>
#include <asm/types.h>
#include "cow.h"
#include "cow_sys.h"

#define PATH_LEN_V1 256

typedef __u32 time32_t;

struct cow_header_v1 {
	__s32 magic;
	__s32 version;
	char backing_file[PATH_LEN_V1];
	time32_t mtime;
	__u64 size;
	__s32 sectorsize;
} __attribute__((packed));

/*
 * Define PATH_LEN_V3 as the usual value of MAXPATHLEN, just hard-code it in
 * case other systems have different values for MAXPATHLEN.
 *
 * The same must hold for V2 - we want file format compatibility, not anything
 * else.
 */
#define PATH_LEN_V3 4096
#define PATH_LEN_V2 PATH_LEN_V3

struct cow_header_v2 {
	__u32 magic;
	__u32 version;
	char backing_file[PATH_LEN_V2];
	time32_t mtime;
	__u64 size;
	__s32 sectorsize;
} __attribute__((packed));

/*
 * Changes from V2 -
 *	PATH_LEN_V3 as described above
 *	Explicitly specify field bit lengths for systems with different
 *		lengths for the usual C types.  Not sure whether char or
 *		time_t should be changed, this can be changed later without
 *		breaking compatibility
 *	Add alignment field so that different alignments can be used for the
 *		bitmap and data
 * 	Add cow_format field to allow for the possibility of different ways
 *		of specifying the COW blocks.  For now, the only value is 0,
 * 		for the traditional COW bitmap.
 *	Move the backing_file field to the end of the header.  This allows
 *		for the possibility of expanding it into the padding required
 *		by the bitmap alignment.
 * 	The bitmap and data portions of the file will be aligned as specified
 * 		by the alignment field.  This is to allow COW files to be
 *		put on devices with restrictions on access alignments, such as
 *		/dev/raw, with a 512 byte alignment restriction.  This also
 *		allows the data to be more aligned more strictly than on
 *		sector boundaries.  This is needed for ubd-mmap, which needs
 *		the data to be page aligned.
 *	Fixed (finally!) the rounding bug
 */

/*
 * Until Dec2005, __attribute__((packed)) was left out from the below
 * definition, leading on 64-bit systems to 4 bytes of padding after mtime, to
 * align size to 8-byte alignment.  This shifted all fields above (no padding
 * was present on 32-bit, no other padding was added).
 *
 * However, this _can be detected_: it means that cow_format (always 0 until
 * now) is shifted onto the first 4 bytes of backing_file, where it is otherwise
 * impossible to find 4 zeros. -bb */

struct cow_header_v3 {
	__u32 magic;
	__u32 version;
	__u32 mtime;
	__u64 size;
	__u32 sectorsize;
	__u32 alignment;
	__u32 cow_format;
	char backing_file[PATH_LEN_V3];
} __attribute__((packed));

/* This is the broken layout used by some 64-bit binaries. */
struct cow_header_v3_broken {
	__u32 magic;
	__u32 version;
	__s64 mtime;
	__u64 size;
	__u32 sectorsize;
	__u32 alignment;
	__u32 cow_format;
	char backing_file[PATH_LEN_V3];
};

/* COW format definitions - for now, we have only the usual COW bitmap */
#define COW_BITMAP 0

union cow_header {
	struct cow_header_v1 v1;
	struct cow_header_v2 v2;
	struct cow_header_v3 v3;
	struct cow_header_v3_broken v3_b;
};

#define COW_MAGIC 0x4f4f4f4d  /* MOOO */
#define COW_VERSION 3

#define DIV_ROUND(x, len) (((x) + (len) - 1) / (len))
#define ROUND_UP(x, align) DIV_ROUND(x, align) * (align)

void cow_sizes(int version, __u64 size, int sectorsize, int align,
	       int bitmap_offset, unsigned long *bitmap_len_out,
	       int *data_offset_out)
{
	if (version < 3) {
		*bitmap_len_out = (size + sectorsize - 1) / (8 * sectorsize);

		*data_offset_out = bitmap_offset + *bitmap_len_out;
		*data_offset_out = (*data_offset_out + sectorsize - 1) /
			sectorsize;
		*data_offset_out *= sectorsize;
	}
	else {
		*bitmap_len_out = DIV_ROUND(size, sectorsize);
		*bitmap_len_out = DIV_ROUND(*bitmap_len_out, 8);

		*data_offset_out = bitmap_offset + *bitmap_len_out;
		*data_offset_out = ROUND_UP(*data_offset_out, align);
	}
}

static int absolutize(char *to, int size, char *from)
{
	char save_cwd[256], *slash;
	int remaining;

	if (getcwd(save_cwd, sizeof(save_cwd)) == NULL) {
		cow_printf("absolutize : unable to get cwd - errno = %d\n",
			   errno);
		return -1;
	}
	slash = strrchr(from, '/');
	if (slash != NULL) {
		*slash = '\0';
		if (chdir(from)) {
			*slash = '/';
			cow_printf("absolutize : Can't cd to '%s' - "
				   "errno = %d\n", from, errno);
			return -1;
		}
		*slash = '/';
		if (getcwd(to, size) == NULL) {
			cow_printf("absolutize : unable to get cwd of '%s' - "
			       "errno = %d\n", from, errno);
			return -1;
		}
		remaining = size - strlen(to);
		if (strlen(slash) + 1 > remaining) {
			cow_printf("absolutize : unable to fit '%s' into %d "
			       "chars\n", from, size);
			return -1;
		}
		strcat(to, slash);
	}
	else {
		if (strlen(save_cwd) + 1 + strlen(from) + 1 > size) {
			cow_printf("absolutize : unable to fit '%s' into %d "
			       "chars\n", from, size);
			return -1;
		}
		strcpy(to, save_cwd);
		strcat(to, "/");
		strcat(to, from);
	}
	chdir(save_cwd);
	return 0;
}

int write_cow_header(char *cow_file, int fd, char *backing_file,
		     int sectorsize, int alignment, unsigned long long *size)
{
	struct cow_header_v3 *header;
	unsigned long modtime;
	int err;

	err = cow_seek_file(fd, 0);
	if (err < 0) {
		cow_printf("write_cow_header - lseek failed, err = %d\n", -err);
		goto out;
	}

	err = -ENOMEM;
	header = cow_malloc(sizeof(*header));
	if (header == NULL) {
		cow_printf("write_cow_header - failed to allocate COW V3 "
			   "header\n");
		goto out;
	}
	header->magic = htonl(COW_MAGIC);
	header->version = htonl(COW_VERSION);

	err = -EINVAL;
	if (strlen(backing_file) > sizeof(header->backing_file) - 1) {
		/* Below, %zd is for a size_t value */
		cow_printf("Backing file name \"%s\" is too long - names are "
			   "limited to %zd characters\n", backing_file,
			   sizeof(header->backing_file) - 1);
		goto out_free;
	}

	if (absolutize(header->backing_file, sizeof(header->backing_file),
		      backing_file))
		goto out_free;

	err = os_file_modtime(header->backing_file, &modtime);
	if (err < 0) {
		cow_printf("write_cow_header - backing file '%s' mtime "
			   "request failed, err = %d\n", header->backing_file,
			   -err);
		goto out_free;
	}

	err = cow_file_size(header->backing_file, size);
	if (err < 0) {
		cow_printf("write_cow_header - couldn't get size of "
			   "backing file '%s', err = %d\n",
			   header->backing_file, -err);
		goto out_free;
	}

	header->mtime = htonl(modtime);
	header->size = htonll(*size);
	header->sectorsize = htonl(sectorsize);
	header->alignment = htonl(alignment);
	header->cow_format = COW_BITMAP;

	err = cow_write_file(fd, header, sizeof(*header));
	if (err != sizeof(*header)) {
		cow_printf("write_cow_header - write of header to "
			   "new COW file '%s' failed, err = %d\n", cow_file,
			   -err);
		goto out_free;
	}
	err = 0;
 out_free:
	cow_free(header);
 out:
	return err;
}

int file_reader(__u64 offset, char *buf, int len, void *arg)
{
	int fd = *((int *) arg);

	return pread(fd, buf, len, offset);
}

/* XXX Need to sanity-check the values read from the header */

int read_cow_header(int (*reader)(__u64, char *, int, void *), void *arg,
		    __u32 *version_out, char **backing_file_out,
		    time_t *mtime_out, unsigned long long *size_out,
		    int *sectorsize_out, __u32 *align_out,
		    int *bitmap_offset_out)
{
	union cow_header *header;
	char *file;
	int err, n;
	unsigned long version, magic;

	header = cow_malloc(sizeof(*header));
	if (header == NULL) {
	        cow_printf("read_cow_header - Failed to allocate header\n");
		return -ENOMEM;
	}
	err = -EINVAL;
	n = (*reader)(0, (char *) header, sizeof(*header), arg);
	if (n < offsetof(typeof(header->v1), backing_file)) {
		cow_printf("read_cow_header - short header\n");
		goto out;
	}

	magic = header->v1.magic;
	if (magic == COW_MAGIC)
		version = header->v1.version;
	else if (magic == ntohl(COW_MAGIC))
		version = ntohl(header->v1.version);
	/* No error printed because the non-COW case comes through here */
	else goto out;

	*version_out = version;

	if (version == 1) {
		if (n < sizeof(header->v1)) {
			cow_printf("read_cow_header - failed to read V1 "
				   "header\n");
			goto out;
		}
		*mtime_out = header->v1.mtime;
		*size_out = header->v1.size;
		*sectorsize_out = header->v1.sectorsize;
		*bitmap_offset_out = sizeof(header->v1);
		*align_out = *sectorsize_out;
		file = header->v1.backing_file;
	}
	else if (version == 2) {
		if (n < sizeof(header->v2)) {
			cow_printf("read_cow_header - failed to read V2 "
				   "header\n");
			goto out;
		}
		*mtime_out = ntohl(header->v2.mtime);
		*size_out = ntohll(header->v2.size);
		*sectorsize_out = ntohl(header->v2.sectorsize);
		*bitmap_offset_out = sizeof(header->v2);
		*align_out = *sectorsize_out;
		file = header->v2.backing_file;
	}
	/* This is very subtle - see above at union cow_header definition */
	else if (version == 3 && (*((int*)header->v3.backing_file) != 0)) {
		if (n < sizeof(header->v3)) {
			cow_printf("read_cow_header - failed to read V3 "
				   "header\n");
			goto out;
		}
		*mtime_out = ntohl(header->v3.mtime);
		*size_out = ntohll(header->v3.size);
		*sectorsize_out = ntohl(header->v3.sectorsize);
		*align_out = ntohl(header->v3.alignment);
		if (*align_out == 0) {
			cow_printf("read_cow_header - invalid COW header, "
				   "align == 0\n");
		}
		*bitmap_offset_out = ROUND_UP(sizeof(header->v3), *align_out);
		file = header->v3.backing_file;
	}
	else if (version == 3) {
		cow_printf("read_cow_header - broken V3 file with"
			   " 64-bit layout - recovering content.\n");

		if (n < sizeof(header->v3_b)) {
			cow_printf("read_cow_header - failed to read V3 "
				   "header\n");
			goto out;
		}

		/*
		 * this was used until Dec2005 - 64bits are needed to represent
		 * 2038+. I.e. we can safely do this truncating cast.
		 *
		 * Additionally, we must use ntohl() instead of ntohll(), since
		 * the program used to use the former (tested - I got mtime
		 * mismatch "0 vs whatever").
		 *
		 * Ever heard about bug-to-bug-compatibility ? ;-) */
		*mtime_out = (time32_t) ntohl(header->v3_b.mtime);

		*size_out = ntohll(header->v3_b.size);
		*sectorsize_out = ntohl(header->v3_b.sectorsize);
		*align_out = ntohl(header->v3_b.alignment);
		if (*align_out == 0) {
			cow_printf("read_cow_header - invalid COW header, "
				   "align == 0\n");
		}
		*bitmap_offset_out = ROUND_UP(sizeof(header->v3_b), *align_out);
		file = header->v3_b.backing_file;
	}
	else {
		cow_printf("read_cow_header - invalid COW version\n");
		goto out;
	}
	err = -ENOMEM;
	*backing_file_out = cow_strdup(file);
	if (*backing_file_out == NULL) {
		cow_printf("read_cow_header - failed to allocate backing "
			   "file\n");
		goto out;
	}
	err = 0;
 out:
	cow_free(header);
	return err;
}

int init_cow_file(int fd, char *cow_file, char *backing_file, int sectorsize,
		  int alignment, int *bitmap_offset_out,
		  unsigned long *bitmap_len_out, int *data_offset_out)
{
	unsigned long long size, offset;
	char zero = 0;
	int err;

	err = write_cow_header(cow_file, fd, backing_file, sectorsize,
			       alignment, &size);
	if (err)
		goto out;

	*bitmap_offset_out = ROUND_UP(sizeof(struct cow_header_v3), alignment);
	cow_sizes(COW_VERSION, size, sectorsize, alignment, *bitmap_offset_out,
		  bitmap_len_out, data_offset_out);

	offset = *data_offset_out + size - sizeof(zero);
	err = cow_seek_file(fd, offset);
	if (err < 0) {
		cow_printf("cow bitmap lseek failed : err = %d\n", -err);
		goto out;
	}

	/*
	 * does not really matter how much we write it is just to set EOF
	 * this also sets the entire COW bitmap
	 * to zero without having to allocate it
	 */
	err = cow_write_file(fd, &zero, sizeof(zero));
	if (err != sizeof(zero)) {
		cow_printf("Write of bitmap to new COW file '%s' failed, "
			   "err = %d\n", cow_file, -err);
		if (err >= 0)
			err = -EINVAL;
		goto out;
	}

	return 0;
 out:
	return err;
}