2 * Copyright (C) 2007 Jeff Dike (jdike@{linux.intel,addtoit}.com)
3 * Licensed under the GPL
7 * _XOPEN_SOURCE is needed for pread, but we define _GNU_SOURCE, which defines
13 #include <arpa/inet.h>
18 #define PATH_LEN_V1 256
20 typedef __u32 time32_t;
22 struct cow_header_v1 {
25 char backing_file[PATH_LEN_V1];
29 } __attribute__((packed));
32 * Define PATH_LEN_V3 as the usual value of MAXPATHLEN, just hard-code it in
33 * case other systems have different values for MAXPATHLEN.
35 * The same must hold for V2 - we want file format compatibility, not anything
38 #define PATH_LEN_V3 4096
39 #define PATH_LEN_V2 PATH_LEN_V3
41 struct cow_header_v2 {
44 char backing_file[PATH_LEN_V2];
48 } __attribute__((packed));
52 * PATH_LEN_V3 as described above
53 * Explicitly specify field bit lengths for systems with different
54 * lengths for the usual C types. Not sure whether char or
55 * time_t should be changed, this can be changed later without
56 * breaking compatibility
57 * Add alignment field so that different alignments can be used for the
59 * Add cow_format field to allow for the possibility of different ways
60 * of specifying the COW blocks. For now, the only value is 0,
61 * for the traditional COW bitmap.
62 * Move the backing_file field to the end of the header. This allows
63 * for the possibility of expanding it into the padding required
64 * by the bitmap alignment.
65 * The bitmap and data portions of the file will be aligned as specified
66 * by the alignment field. This is to allow COW files to be
67 * put on devices with restrictions on access alignments, such as
68 * /dev/raw, with a 512 byte alignment restriction. This also
69 * allows the data to be more aligned more strictly than on
70 * sector boundaries. This is needed for ubd-mmap, which needs
71 * the data to be page aligned.
72 * Fixed (finally!) the rounding bug
76 * Until Dec2005, __attribute__((packed)) was left out from the below
77 * definition, leading on 64-bit systems to 4 bytes of padding after mtime, to
78 * align size to 8-byte alignment. This shifted all fields above (no padding
79 * was present on 32-bit, no other padding was added).
81 * However, this _can be detected_: it means that cow_format (always 0 until
82 * now) is shifted onto the first 4 bytes of backing_file, where it is otherwise
83 * impossible to find 4 zeros. -bb */
85 struct cow_header_v3 {
93 char backing_file[PATH_LEN_V3];
94 } __attribute__((packed));
96 /* This is the broken layout used by some 64-bit binaries. */
97 struct cow_header_v3_broken {
105 char backing_file[PATH_LEN_V3];
108 /* COW format definitions - for now, we have only the usual COW bitmap */
112 struct cow_header_v1 v1;
113 struct cow_header_v2 v2;
114 struct cow_header_v3 v3;
115 struct cow_header_v3_broken v3_b;
118 #define COW_MAGIC 0x4f4f4f4d /* MOOO */
119 #define COW_VERSION 3
121 #define DIV_ROUND(x, len) (((x) + (len) - 1) / (len))
122 #define ROUND_UP(x, align) DIV_ROUND(x, align) * (align)
124 void cow_sizes(int version, __u64 size, int sectorsize, int align,
125 int bitmap_offset, unsigned long *bitmap_len_out,
126 int *data_offset_out)
129 *bitmap_len_out = (size + sectorsize - 1) / (8 * sectorsize);
131 *data_offset_out = bitmap_offset + *bitmap_len_out;
132 *data_offset_out = (*data_offset_out + sectorsize - 1) /
134 *data_offset_out *= sectorsize;
137 *bitmap_len_out = DIV_ROUND(size, sectorsize);
138 *bitmap_len_out = DIV_ROUND(*bitmap_len_out, 8);
140 *data_offset_out = bitmap_offset + *bitmap_len_out;
141 *data_offset_out = ROUND_UP(*data_offset_out, align);
145 static int absolutize(char *to, int size, char *from)
147 char save_cwd[256], *slash;
150 if (getcwd(save_cwd, sizeof(save_cwd)) == NULL) {
151 cow_printf("absolutize : unable to get cwd - errno = %d\n",
155 slash = strrchr(from, '/');
160 cow_printf("absolutize : Can't cd to '%s' - "
161 "errno = %d\n", from, errno);
165 if (getcwd(to, size) == NULL) {
166 cow_printf("absolutize : unable to get cwd of '%s' - "
167 "errno = %d\n", from, errno);
170 remaining = size - strlen(to);
171 if (strlen(slash) + 1 > remaining) {
172 cow_printf("absolutize : unable to fit '%s' into %d "
173 "chars\n", from, size);
179 if (strlen(save_cwd) + 1 + strlen(from) + 1 > size) {
180 cow_printf("absolutize : unable to fit '%s' into %d "
181 "chars\n", from, size);
184 strcpy(to, save_cwd);
188 if (chdir(save_cwd)) {
189 cow_printf("absolutize : Can't cd to '%s' - "
190 "errno = %d\n", save_cwd, errno);
196 int write_cow_header(char *cow_file, int fd, char *backing_file,
197 int sectorsize, int alignment, unsigned long long *size)
199 struct cow_header_v3 *header;
200 unsigned long modtime;
203 err = cow_seek_file(fd, 0);
205 cow_printf("write_cow_header - lseek failed, err = %d\n", -err);
210 header = cow_malloc(sizeof(*header));
211 if (header == NULL) {
212 cow_printf("write_cow_header - failed to allocate COW V3 "
216 header->magic = htobe32(COW_MAGIC);
217 header->version = htobe32(COW_VERSION);
220 if (strlen(backing_file) > sizeof(header->backing_file) - 1) {
221 /* Below, %zd is for a size_t value */
222 cow_printf("Backing file name \"%s\" is too long - names are "
223 "limited to %zd characters\n", backing_file,
224 sizeof(header->backing_file) - 1);
228 if (absolutize(header->backing_file, sizeof(header->backing_file),
232 err = os_file_modtime(header->backing_file, &modtime);
234 cow_printf("write_cow_header - backing file '%s' mtime "
235 "request failed, err = %d\n", header->backing_file,
240 err = cow_file_size(header->backing_file, size);
242 cow_printf("write_cow_header - couldn't get size of "
243 "backing file '%s', err = %d\n",
244 header->backing_file, -err);
248 header->mtime = htobe32(modtime);
249 header->size = htobe64(*size);
250 header->sectorsize = htobe32(sectorsize);
251 header->alignment = htobe32(alignment);
252 header->cow_format = COW_BITMAP;
254 err = cow_write_file(fd, header, sizeof(*header));
255 if (err != sizeof(*header)) {
256 cow_printf("write_cow_header - write of header to "
257 "new COW file '%s' failed, err = %d\n", cow_file,
268 int file_reader(__u64 offset, char *buf, int len, void *arg)
270 int fd = *((int *) arg);
272 return pread(fd, buf, len, offset);
275 /* XXX Need to sanity-check the values read from the header */
277 int read_cow_header(int (*reader)(__u64, char *, int, void *), void *arg,
278 __u32 *version_out, char **backing_file_out,
279 time_t *mtime_out, unsigned long long *size_out,
280 int *sectorsize_out, __u32 *align_out,
281 int *bitmap_offset_out)
283 union cow_header *header;
286 unsigned long version, magic;
288 header = cow_malloc(sizeof(*header));
289 if (header == NULL) {
290 cow_printf("read_cow_header - Failed to allocate header\n");
294 n = (*reader)(0, (char *) header, sizeof(*header), arg);
295 if (n < offsetof(typeof(header->v1), backing_file)) {
296 cow_printf("read_cow_header - short header\n");
300 magic = header->v1.magic;
301 if (magic == COW_MAGIC)
302 version = header->v1.version;
303 else if (magic == be32toh(COW_MAGIC))
304 version = be32toh(header->v1.version);
305 /* No error printed because the non-COW case comes through here */
308 *version_out = version;
311 if (n < sizeof(header->v1)) {
312 cow_printf("read_cow_header - failed to read V1 "
316 *mtime_out = header->v1.mtime;
317 *size_out = header->v1.size;
318 *sectorsize_out = header->v1.sectorsize;
319 *bitmap_offset_out = sizeof(header->v1);
320 *align_out = *sectorsize_out;
321 file = header->v1.backing_file;
323 else if (version == 2) {
324 if (n < sizeof(header->v2)) {
325 cow_printf("read_cow_header - failed to read V2 "
329 *mtime_out = be32toh(header->v2.mtime);
330 *size_out = be64toh(header->v2.size);
331 *sectorsize_out = be32toh(header->v2.sectorsize);
332 *bitmap_offset_out = sizeof(header->v2);
333 *align_out = *sectorsize_out;
334 file = header->v2.backing_file;
336 /* This is very subtle - see above at union cow_header definition */
337 else if (version == 3 && (*((int*)header->v3.backing_file) != 0)) {
338 if (n < sizeof(header->v3)) {
339 cow_printf("read_cow_header - failed to read V3 "
343 *mtime_out = be32toh(header->v3.mtime);
344 *size_out = be64toh(header->v3.size);
345 *sectorsize_out = be32toh(header->v3.sectorsize);
346 *align_out = be32toh(header->v3.alignment);
347 if (*align_out == 0) {
348 cow_printf("read_cow_header - invalid COW header, "
351 *bitmap_offset_out = ROUND_UP(sizeof(header->v3), *align_out);
352 file = header->v3.backing_file;
354 else if (version == 3) {
355 cow_printf("read_cow_header - broken V3 file with"
356 " 64-bit layout - recovering content.\n");
358 if (n < sizeof(header->v3_b)) {
359 cow_printf("read_cow_header - failed to read V3 "
365 * this was used until Dec2005 - 64bits are needed to represent
366 * 2038+. I.e. we can safely do this truncating cast.
368 * Additionally, we must use be32toh() instead of be64toh(), since
369 * the program used to use the former (tested - I got mtime
370 * mismatch "0 vs whatever").
372 * Ever heard about bug-to-bug-compatibility ? ;-) */
373 *mtime_out = (time32_t) be32toh(header->v3_b.mtime);
375 *size_out = be64toh(header->v3_b.size);
376 *sectorsize_out = be32toh(header->v3_b.sectorsize);
377 *align_out = be32toh(header->v3_b.alignment);
378 if (*align_out == 0) {
379 cow_printf("read_cow_header - invalid COW header, "
382 *bitmap_offset_out = ROUND_UP(sizeof(header->v3_b), *align_out);
383 file = header->v3_b.backing_file;
386 cow_printf("read_cow_header - invalid COW version\n");
390 *backing_file_out = cow_strdup(file);
391 if (*backing_file_out == NULL) {
392 cow_printf("read_cow_header - failed to allocate backing "
402 int init_cow_file(int fd, char *cow_file, char *backing_file, int sectorsize,
403 int alignment, int *bitmap_offset_out,
404 unsigned long *bitmap_len_out, int *data_offset_out)
406 unsigned long long size, offset;
410 err = write_cow_header(cow_file, fd, backing_file, sectorsize,
415 *bitmap_offset_out = ROUND_UP(sizeof(struct cow_header_v3), alignment);
416 cow_sizes(COW_VERSION, size, sectorsize, alignment, *bitmap_offset_out,
417 bitmap_len_out, data_offset_out);
419 offset = *data_offset_out + size - sizeof(zero);
420 err = cow_seek_file(fd, offset);
422 cow_printf("cow bitmap lseek failed : err = %d\n", -err);
427 * does not really matter how much we write it is just to set EOF
428 * this also sets the entire COW bitmap
429 * to zero without having to allocate it
431 err = cow_write_file(fd, &zero, sizeof(zero));
432 if (err != sizeof(zero)) {
433 cow_printf("Write of bitmap to new COW file '%s' failed, "
434 "err = %d\n", cow_file, -err);