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Linux/arch/um/drivers/cow_user.c

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  1 /*
  2  * Copyright (C) 2007 Jeff Dike (jdike@{linux.intel,addtoit}.com)
  3  * Licensed under the GPL
  4  */
  5 
  6 /*
  7  * _XOPEN_SOURCE is needed for pread, but we define _GNU_SOURCE, which defines
  8  * that.
  9  */
 10 #include <unistd.h>
 11 #include <byteswap.h>
 12 #include <errno.h>
 13 #include <string.h>
 14 #include <arpa/inet.h>
 15 #include <asm/types.h>
 16 #include "cow.h"
 17 #include "cow_sys.h"
 18 
 19 #define PATH_LEN_V1 256
 20 
 21 typedef __u32 time32_t;
 22 
 23 struct cow_header_v1 {
 24         __s32 magic;
 25         __s32 version;
 26         char backing_file[PATH_LEN_V1];
 27         time32_t mtime;
 28         __u64 size;
 29         __s32 sectorsize;
 30 } __attribute__((packed));
 31 
 32 /*
 33  * Define PATH_LEN_V3 as the usual value of MAXPATHLEN, just hard-code it in
 34  * case other systems have different values for MAXPATHLEN.
 35  *
 36  * The same must hold for V2 - we want file format compatibility, not anything
 37  * else.
 38  */
 39 #define PATH_LEN_V3 4096
 40 #define PATH_LEN_V2 PATH_LEN_V3
 41 
 42 struct cow_header_v2 {
 43         __u32 magic;
 44         __u32 version;
 45         char backing_file[PATH_LEN_V2];
 46         time32_t mtime;
 47         __u64 size;
 48         __s32 sectorsize;
 49 } __attribute__((packed));
 50 
 51 /*
 52  * Changes from V2 -
 53  *      PATH_LEN_V3 as described above
 54  *      Explicitly specify field bit lengths for systems with different
 55  *              lengths for the usual C types.  Not sure whether char or
 56  *              time_t should be changed, this can be changed later without
 57  *              breaking compatibility
 58  *      Add alignment field so that different alignments can be used for the
 59  *              bitmap and data
 60  *      Add cow_format field to allow for the possibility of different ways
 61  *              of specifying the COW blocks.  For now, the only value is 0,
 62  *              for the traditional COW bitmap.
 63  *      Move the backing_file field to the end of the header.  This allows
 64  *              for the possibility of expanding it into the padding required
 65  *              by the bitmap alignment.
 66  *      The bitmap and data portions of the file will be aligned as specified
 67  *              by the alignment field.  This is to allow COW files to be
 68  *              put on devices with restrictions on access alignments, such as
 69  *              /dev/raw, with a 512 byte alignment restriction.  This also
 70  *              allows the data to be more aligned more strictly than on
 71  *              sector boundaries.  This is needed for ubd-mmap, which needs
 72  *              the data to be page aligned.
 73  *      Fixed (finally!) the rounding bug
 74  */
 75 
 76 /*
 77  * Until Dec2005, __attribute__((packed)) was left out from the below
 78  * definition, leading on 64-bit systems to 4 bytes of padding after mtime, to
 79  * align size to 8-byte alignment.  This shifted all fields above (no padding
 80  * was present on 32-bit, no other padding was added).
 81  *
 82  * However, this _can be detected_: it means that cow_format (always 0 until
 83  * now) is shifted onto the first 4 bytes of backing_file, where it is otherwise
 84  * impossible to find 4 zeros. -bb */
 85 
 86 struct cow_header_v3 {
 87         __u32 magic;
 88         __u32 version;
 89         __u32 mtime;
 90         __u64 size;
 91         __u32 sectorsize;
 92         __u32 alignment;
 93         __u32 cow_format;
 94         char backing_file[PATH_LEN_V3];
 95 } __attribute__((packed));
 96 
 97 /* This is the broken layout used by some 64-bit binaries. */
 98 struct cow_header_v3_broken {
 99         __u32 magic;
100         __u32 version;
101         __s64 mtime;
102         __u64 size;
103         __u32 sectorsize;
104         __u32 alignment;
105         __u32 cow_format;
106         char backing_file[PATH_LEN_V3];
107 };
108 
109 /* COW format definitions - for now, we have only the usual COW bitmap */
110 #define COW_BITMAP 0
111 
112 union cow_header {
113         struct cow_header_v1 v1;
114         struct cow_header_v2 v2;
115         struct cow_header_v3 v3;
116         struct cow_header_v3_broken v3_b;
117 };
118 
119 #define COW_MAGIC 0x4f4f4f4d  /* MOOO */
120 #define COW_VERSION 3
121 
122 #define DIV_ROUND(x, len) (((x) + (len) - 1) / (len))
123 #define ROUND_UP(x, align) DIV_ROUND(x, align) * (align)
124 
125 void cow_sizes(int version, __u64 size, int sectorsize, int align,
126                int bitmap_offset, unsigned long *bitmap_len_out,
127                int *data_offset_out)
128 {
129         if (version < 3) {
130                 *bitmap_len_out = (size + sectorsize - 1) / (8 * sectorsize);
131 
132                 *data_offset_out = bitmap_offset + *bitmap_len_out;
133                 *data_offset_out = (*data_offset_out + sectorsize - 1) /
134                         sectorsize;
135                 *data_offset_out *= sectorsize;
136         }
137         else {
138                 *bitmap_len_out = DIV_ROUND(size, sectorsize);
139                 *bitmap_len_out = DIV_ROUND(*bitmap_len_out, 8);
140 
141                 *data_offset_out = bitmap_offset + *bitmap_len_out;
142                 *data_offset_out = ROUND_UP(*data_offset_out, align);
143         }
144 }
145 
146 static int absolutize(char *to, int size, char *from)
147 {
148         char save_cwd[256], *slash;
149         int remaining;
150 
151         if (getcwd(save_cwd, sizeof(save_cwd)) == NULL) {
152                 cow_printf("absolutize : unable to get cwd - errno = %d\n",
153                            errno);
154                 return -1;
155         }
156         slash = strrchr(from, '/');
157         if (slash != NULL) {
158                 *slash = '\0';
159                 if (chdir(from)) {
160                         *slash = '/';
161                         cow_printf("absolutize : Can't cd to '%s' - "
162                                    "errno = %d\n", from, errno);
163                         return -1;
164                 }
165                 *slash = '/';
166                 if (getcwd(to, size) == NULL) {
167                         cow_printf("absolutize : unable to get cwd of '%s' - "
168                                "errno = %d\n", from, errno);
169                         return -1;
170                 }
171                 remaining = size - strlen(to);
172                 if (strlen(slash) + 1 > remaining) {
173                         cow_printf("absolutize : unable to fit '%s' into %d "
174                                "chars\n", from, size);
175                         return -1;
176                 }
177                 strcat(to, slash);
178         }
179         else {
180                 if (strlen(save_cwd) + 1 + strlen(from) + 1 > size) {
181                         cow_printf("absolutize : unable to fit '%s' into %d "
182                                "chars\n", from, size);
183                         return -1;
184                 }
185                 strcpy(to, save_cwd);
186                 strcat(to, "/");
187                 strcat(to, from);
188         }
189         chdir(save_cwd);
190         return 0;
191 }
192 
193 int write_cow_header(char *cow_file, int fd, char *backing_file,
194                      int sectorsize, int alignment, unsigned long long *size)
195 {
196         struct cow_header_v3 *header;
197         unsigned long modtime;
198         int err;
199 
200         err = cow_seek_file(fd, 0);
201         if (err < 0) {
202                 cow_printf("write_cow_header - lseek failed, err = %d\n", -err);
203                 goto out;
204         }
205 
206         err = -ENOMEM;
207         header = cow_malloc(sizeof(*header));
208         if (header == NULL) {
209                 cow_printf("write_cow_header - failed to allocate COW V3 "
210                            "header\n");
211                 goto out;
212         }
213         header->magic = htonl(COW_MAGIC);
214         header->version = htonl(COW_VERSION);
215 
216         err = -EINVAL;
217         if (strlen(backing_file) > sizeof(header->backing_file) - 1) {
218                 /* Below, %zd is for a size_t value */
219                 cow_printf("Backing file name \"%s\" is too long - names are "
220                            "limited to %zd characters\n", backing_file,
221                            sizeof(header->backing_file) - 1);
222                 goto out_free;
223         }
224 
225         if (absolutize(header->backing_file, sizeof(header->backing_file),
226                       backing_file))
227                 goto out_free;
228 
229         err = os_file_modtime(header->backing_file, &modtime);
230         if (err < 0) {
231                 cow_printf("write_cow_header - backing file '%s' mtime "
232                            "request failed, err = %d\n", header->backing_file,
233                            -err);
234                 goto out_free;
235         }
236 
237         err = cow_file_size(header->backing_file, size);
238         if (err < 0) {
239                 cow_printf("write_cow_header - couldn't get size of "
240                            "backing file '%s', err = %d\n",
241                            header->backing_file, -err);
242                 goto out_free;
243         }
244 
245         header->mtime = htonl(modtime);
246         header->size = htonll(*size);
247         header->sectorsize = htonl(sectorsize);
248         header->alignment = htonl(alignment);
249         header->cow_format = COW_BITMAP;
250 
251         err = cow_write_file(fd, header, sizeof(*header));
252         if (err != sizeof(*header)) {
253                 cow_printf("write_cow_header - write of header to "
254                            "new COW file '%s' failed, err = %d\n", cow_file,
255                            -err);
256                 goto out_free;
257         }
258         err = 0;
259  out_free:
260         cow_free(header);
261  out:
262         return err;
263 }
264 
265 int file_reader(__u64 offset, char *buf, int len, void *arg)
266 {
267         int fd = *((int *) arg);
268 
269         return pread(fd, buf, len, offset);
270 }
271 
272 /* XXX Need to sanity-check the values read from the header */
273 
274 int read_cow_header(int (*reader)(__u64, char *, int, void *), void *arg,
275                     __u32 *version_out, char **backing_file_out,
276                     time_t *mtime_out, unsigned long long *size_out,
277                     int *sectorsize_out, __u32 *align_out,
278                     int *bitmap_offset_out)
279 {
280         union cow_header *header;
281         char *file;
282         int err, n;
283         unsigned long version, magic;
284 
285         header = cow_malloc(sizeof(*header));
286         if (header == NULL) {
287                 cow_printf("read_cow_header - Failed to allocate header\n");
288                 return -ENOMEM;
289         }
290         err = -EINVAL;
291         n = (*reader)(0, (char *) header, sizeof(*header), arg);
292         if (n < offsetof(typeof(header->v1), backing_file)) {
293                 cow_printf("read_cow_header - short header\n");
294                 goto out;
295         }
296 
297         magic = header->v1.magic;
298         if (magic == COW_MAGIC)
299                 version = header->v1.version;
300         else if (magic == ntohl(COW_MAGIC))
301                 version = ntohl(header->v1.version);
302         /* No error printed because the non-COW case comes through here */
303         else goto out;
304 
305         *version_out = version;
306 
307         if (version == 1) {
308                 if (n < sizeof(header->v1)) {
309                         cow_printf("read_cow_header - failed to read V1 "
310                                    "header\n");
311                         goto out;
312                 }
313                 *mtime_out = header->v1.mtime;
314                 *size_out = header->v1.size;
315                 *sectorsize_out = header->v1.sectorsize;
316                 *bitmap_offset_out = sizeof(header->v1);
317                 *align_out = *sectorsize_out;
318                 file = header->v1.backing_file;
319         }
320         else if (version == 2) {
321                 if (n < sizeof(header->v2)) {
322                         cow_printf("read_cow_header - failed to read V2 "
323                                    "header\n");
324                         goto out;
325                 }
326                 *mtime_out = ntohl(header->v2.mtime);
327                 *size_out = ntohll(header->v2.size);
328                 *sectorsize_out = ntohl(header->v2.sectorsize);
329                 *bitmap_offset_out = sizeof(header->v2);
330                 *align_out = *sectorsize_out;
331                 file = header->v2.backing_file;
332         }
333         /* This is very subtle - see above at union cow_header definition */
334         else if (version == 3 && (*((int*)header->v3.backing_file) != 0)) {
335                 if (n < sizeof(header->v3)) {
336                         cow_printf("read_cow_header - failed to read V3 "
337                                    "header\n");
338                         goto out;
339                 }
340                 *mtime_out = ntohl(header->v3.mtime);
341                 *size_out = ntohll(header->v3.size);
342                 *sectorsize_out = ntohl(header->v3.sectorsize);
343                 *align_out = ntohl(header->v3.alignment);
344                 if (*align_out == 0) {
345                         cow_printf("read_cow_header - invalid COW header, "
346                                    "align == 0\n");
347                 }
348                 *bitmap_offset_out = ROUND_UP(sizeof(header->v3), *align_out);
349                 file = header->v3.backing_file;
350         }
351         else if (version == 3) {
352                 cow_printf("read_cow_header - broken V3 file with"
353                            " 64-bit layout - recovering content.\n");
354 
355                 if (n < sizeof(header->v3_b)) {
356                         cow_printf("read_cow_header - failed to read V3 "
357                                    "header\n");
358                         goto out;
359                 }
360 
361                 /*
362                  * this was used until Dec2005 - 64bits are needed to represent
363                  * 2038+. I.e. we can safely do this truncating cast.
364                  *
365                  * Additionally, we must use ntohl() instead of ntohll(), since
366                  * the program used to use the former (tested - I got mtime
367                  * mismatch "0 vs whatever").
368                  *
369                  * Ever heard about bug-to-bug-compatibility ? ;-) */
370                 *mtime_out = (time32_t) ntohl(header->v3_b.mtime);
371 
372                 *size_out = ntohll(header->v3_b.size);
373                 *sectorsize_out = ntohl(header->v3_b.sectorsize);
374                 *align_out = ntohl(header->v3_b.alignment);
375                 if (*align_out == 0) {
376                         cow_printf("read_cow_header - invalid COW header, "
377                                    "align == 0\n");
378                 }
379                 *bitmap_offset_out = ROUND_UP(sizeof(header->v3_b), *align_out);
380                 file = header->v3_b.backing_file;
381         }
382         else {
383                 cow_printf("read_cow_header - invalid COW version\n");
384                 goto out;
385         }
386         err = -ENOMEM;
387         *backing_file_out = cow_strdup(file);
388         if (*backing_file_out == NULL) {
389                 cow_printf("read_cow_header - failed to allocate backing "
390                            "file\n");
391                 goto out;
392         }
393         err = 0;
394  out:
395         cow_free(header);
396         return err;
397 }
398 
399 int init_cow_file(int fd, char *cow_file, char *backing_file, int sectorsize,
400                   int alignment, int *bitmap_offset_out,
401                   unsigned long *bitmap_len_out, int *data_offset_out)
402 {
403         unsigned long long size, offset;
404         char zero = 0;
405         int err;
406 
407         err = write_cow_header(cow_file, fd, backing_file, sectorsize,
408                                alignment, &size);
409         if (err)
410                 goto out;
411 
412         *bitmap_offset_out = ROUND_UP(sizeof(struct cow_header_v3), alignment);
413         cow_sizes(COW_VERSION, size, sectorsize, alignment, *bitmap_offset_out,
414                   bitmap_len_out, data_offset_out);
415 
416         offset = *data_offset_out + size - sizeof(zero);
417         err = cow_seek_file(fd, offset);
418         if (err < 0) {
419                 cow_printf("cow bitmap lseek failed : err = %d\n", -err);
420                 goto out;
421         }
422 
423         /*
424          * does not really matter how much we write it is just to set EOF
425          * this also sets the entire COW bitmap
426          * to zero without having to allocate it
427          */
428         err = cow_write_file(fd, &zero, sizeof(zero));
429         if (err != sizeof(zero)) {
430                 cow_printf("Write of bitmap to new COW file '%s' failed, "
431                            "err = %d\n", cow_file, -err);
432                 if (err >= 0)
433                         err = -EINVAL;
434                 goto out;
435         }
436 
437         return 0;
438  out:
439         return err;
440 }
441 

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