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authorPaolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>2006-04-11 01:53:30 -0400
committerLinus Torvalds <torvalds@g5.osdl.org>2006-04-11 09:18:35 -0400
commitf2ea394082c5d1682e6a131c5981085b8752c6e9 (patch)
treeb7789cee4e6484d5063a28a59dcf320ee4676017 /arch
parentcda402b283c34a24b091f78eee116963e9494762 (diff)
[PATCH] uml: safe migration path to the correct V3 COW format
- Correct the layout of all header versions - make all them well-specified for any external event. As we don't have 1-byte or 2-byte wide fields, the 32-bit layout (historical one) has no extra padding, so we can safely add __attribute__((packed)). - Add detection and reading of the broken 64-bit COW format which has been around for a while - to allow safe migration to the correct 32-bit format. Safe detection is possible, thanks to some luck with the existing format, and it works in practice. Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it> Cc: Jeff Dike <jdike@addtoit.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'arch')
-rw-r--r--arch/um/drivers/cow_user.c91
1 files changed, 76 insertions, 15 deletions
diff --git a/arch/um/drivers/cow_user.c b/arch/um/drivers/cow_user.c
index afdf1ea0f557..a9afccf68e38 100644
--- a/arch/um/drivers/cow_user.c
+++ b/arch/um/drivers/cow_user.c
@@ -17,30 +17,34 @@
17 17
18#define PATH_LEN_V1 256 18#define PATH_LEN_V1 256
19 19
20typedef __u32 time32_t;
21
20struct cow_header_v1 { 22struct cow_header_v1 {
21 int magic; 23 __s32 magic;
22 int version; 24 __s32 version;
23 char backing_file[PATH_LEN_V1]; 25 char backing_file[PATH_LEN_V1];
24 time_t mtime; 26 time32_t mtime;
25 __u64 size; 27 __u64 size;
26 int sectorsize; 28 __s32 sectorsize;
27}; 29} __attribute__((packed));
28 30
29#define PATH_LEN_V2 MAXPATHLEN 31/* Define PATH_LEN_V3 as the usual value of MAXPATHLEN, just hard-code it in
32 * case other systems have different values for MAXPATHLEN.
33 *
34 * The same must hold for V2 - we want file format compatibility, not anything
35 * else.
36 */
37#define PATH_LEN_V3 4096
38#define PATH_LEN_V2 PATH_LEN_V3
30 39
31struct cow_header_v2 { 40struct cow_header_v2 {
32 __u32 magic; 41 __u32 magic;
33 __u32 version; 42 __u32 version;
34 char backing_file[PATH_LEN_V2]; 43 char backing_file[PATH_LEN_V2];
35 time_t mtime; 44 time32_t mtime;
36 __u64 size; 45 __u64 size;
37 int sectorsize; 46 __s32 sectorsize;
38}; 47} __attribute__((packed));
39
40/* Define PATH_LEN_V3 as the usual value of MAXPATHLEN, just hard-code it in
41 * case other systems have different values for MAXPATHLEN
42 */
43#define PATH_LEN_V3 4096
44 48
45/* Changes from V2 - 49/* Changes from V2 -
46 * PATH_LEN_V3 as described above 50 * PATH_LEN_V3 as described above
@@ -66,6 +70,15 @@ struct cow_header_v2 {
66 * Fixed (finally!) the rounding bug 70 * Fixed (finally!) the rounding bug
67 */ 71 */
68 72
73/* Until Dec2005, __attribute__((packed)) was left out from the below
74 * definition, leading on 64-bit systems to 4 bytes of padding after mtime, to
75 * align size to 8-byte alignment. This shifted all fields above (no padding
76 * was present on 32-bit, no other padding was added).
77 *
78 * However, this _can be detected_: it means that cow_format (always 0 until
79 * now) is shifted onto the first 4 bytes of backing_file, where it is otherwise
80 * impossible to find 4 zeros. -bb */
81
69struct cow_header_v3 { 82struct cow_header_v3 {
70 __u32 magic; 83 __u32 magic;
71 __u32 version; 84 __u32 version;
@@ -77,6 +90,18 @@ struct cow_header_v3 {
77 char backing_file[PATH_LEN_V3]; 90 char backing_file[PATH_LEN_V3];
78} __attribute__((packed)); 91} __attribute__((packed));
79 92
93/* This is the broken layout used by some 64-bit binaries. */
94struct cow_header_v3_broken {
95 __u32 magic;
96 __u32 version;
97 __s64 mtime;
98 __u64 size;
99 __u32 sectorsize;
100 __u32 alignment;
101 __u32 cow_format;
102 char backing_file[PATH_LEN_V3];
103};
104
80/* COW format definitions - for now, we have only the usual COW bitmap */ 105/* COW format definitions - for now, we have only the usual COW bitmap */
81#define COW_BITMAP 0 106#define COW_BITMAP 0
82 107
@@ -84,6 +109,7 @@ union cow_header {
84 struct cow_header_v1 v1; 109 struct cow_header_v1 v1;
85 struct cow_header_v2 v2; 110 struct cow_header_v2 v2;
86 struct cow_header_v3 v3; 111 struct cow_header_v3 v3;
112 struct cow_header_v3_broken v3_b;
87}; 113};
88 114
89#define COW_MAGIC 0x4f4f4f4d /* MOOO */ 115#define COW_MAGIC 0x4f4f4f4d /* MOOO */
@@ -300,7 +326,8 @@ int read_cow_header(int (*reader)(__u64, char *, int, void *), void *arg,
300 *align_out = *sectorsize_out; 326 *align_out = *sectorsize_out;
301 file = header->v2.backing_file; 327 file = header->v2.backing_file;
302 } 328 }
303 else if(version == 3){ 329 /* This is very subtle - see above at union cow_header definition */
330 else if(version == 3 && (*((int*)header->v3.backing_file) != 0)){
304 if(n < sizeof(header->v3)){ 331 if(n < sizeof(header->v3)){
305 cow_printf("read_cow_header - failed to read V3 " 332 cow_printf("read_cow_header - failed to read V3 "
306 "header\n"); 333 "header\n");
@@ -310,9 +337,43 @@ int read_cow_header(int (*reader)(__u64, char *, int, void *), void *arg,
310 *size_out = ntohll(header->v3.size); 337 *size_out = ntohll(header->v3.size);
311 *sectorsize_out = ntohl(header->v3.sectorsize); 338 *sectorsize_out = ntohl(header->v3.sectorsize);
312 *align_out = ntohl(header->v3.alignment); 339 *align_out = ntohl(header->v3.alignment);
340 if (*align_out == 0) {
341 cow_printf("read_cow_header - invalid COW header, "
342 "align == 0\n");
343 }
313 *bitmap_offset_out = ROUND_UP(sizeof(header->v3), *align_out); 344 *bitmap_offset_out = ROUND_UP(sizeof(header->v3), *align_out);
314 file = header->v3.backing_file; 345 file = header->v3.backing_file;
315 } 346 }
347 else if(version == 3){
348 cow_printf("read_cow_header - broken V3 file with"
349 " 64-bit layout - recovering content.\n");
350
351 if(n < sizeof(header->v3_b)){
352 cow_printf("read_cow_header - failed to read V3 "
353 "header\n");
354 goto out;
355 }
356
357 /* this was used until Dec2005 - 64bits are needed to represent
358 * 2038+. I.e. we can safely do this truncating cast.
359 *
360 * Additionally, we must use ntohl() instead of ntohll(), since
361 * the program used to use the former (tested - I got mtime
362 * mismatch "0 vs whatever").
363 *
364 * Ever heard about bug-to-bug-compatibility ? ;-) */
365 *mtime_out = (time32_t) ntohl(header->v3_b.mtime);
366
367 *size_out = ntohll(header->v3_b.size);
368 *sectorsize_out = ntohl(header->v3_b.sectorsize);
369 *align_out = ntohl(header->v3_b.alignment);
370 if (*align_out == 0) {
371 cow_printf("read_cow_header - invalid COW header, "
372 "align == 0\n");
373 }
374 *bitmap_offset_out = ROUND_UP(sizeof(header->v3_b), *align_out);
375 file = header->v3_b.backing_file;
376 }
316 else { 377 else {
317 cow_printf("read_cow_header - invalid COW version\n"); 378 cow_printf("read_cow_header - invalid COW version\n");
318 goto out; 379 goto out;