[linux-2.6-block.git] / arch / um / drivers / cow_user.c

#include <stddef.h>
#include <string.h>
#include <errno.h>
/* _XOPEN_SOURCE is needed for pread, but we define _GNU_SOURCE, which defines
 * that.
 */
#include <unistd.h>
#include <byteswap.h>
#include <sys/time.h>
#include <sys/param.h>
#include <sys/user.h>

#include "os.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){
		cow_printf("Backing file name \"%s\" is too long - names are "
			   "limited to %d 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);
}

/*
 * ---------------------------------------------------------------------------
 * Local variables:
 * c-file-style: "linux"
 * End:
 */
Commit	Line	Data
1da177e4 LT	1	#include <stddef.h>
	2	#include <string.h>
	3	#include <errno.h>
	4	/* _XOPEN_SOURCE is needed for pread, but we define _GNU_SOURCE, which defines
	5	* that.
	6	*/
	7	#include <unistd.h>
	8	#include <byteswap.h>
	9	#include <sys/time.h>
	10	#include <sys/param.h>
	11	#include <sys/user.h>
1da177e4 LT	12
	13	#include "os.h"
	14
	15	#include "cow.h"
	16	#include "cow_sys.h"
	17
	18	#define PATH_LEN_V1 256
	19
f2ea3940 PBG	20	typedef __u32 time32_t;
f2ea3940 PBG	21
1da177e4	22	struct cow_header_v1 {
f2ea3940 PBG	23	__s32 magic;
f2ea3940 PBG	24	__s32 version;
1da177e4	25	char backing_file[PATH_LEN_V1];
f2ea3940	26	time32_t mtime;
1da177e4	27	__u64 size;
f2ea3940 PBG	28	__s32 sectorsize;
f2ea3940 PBG	29	} __attribute__((packed));
1da177e4	30
f2ea3940 PBG	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
1da177e4 LT	39
	40	struct cow_header_v2 {
	41	__u32 magic;
	42	__u32 version;
	43	char backing_file[PATH_LEN_V2];
f2ea3940	44	time32_t mtime;
1da177e4	45	__u64 size;
f2ea3940 PBG	46	__s32 sectorsize;
f2ea3940 PBG	47	} __attribute__((packed));
1da177e4 LT	48
	49	/* Changes from V2 -
	50	* PATH_LEN_V3 as described above
	51	* Explicitly specify field bit lengths for systems with different
	52	* lengths for the usual C types. Not sure whether char or
	53	* time_t should be changed, this can be changed later without
	54	* breaking compatibility
	55	* Add alignment field so that different alignments can be used for the
	56	* bitmap and data
	57	* Add cow_format field to allow for the possibility of different ways
	58	* of specifying the COW blocks. For now, the only value is 0,
	59	* for the traditional COW bitmap.
	60	* Move the backing_file field to the end of the header. This allows
	61	* for the possibility of expanding it into the padding required
	62	* by the bitmap alignment.
	63	* The bitmap and data portions of the file will be aligned as specified
	64	* by the alignment field. This is to allow COW files to be
	65	* put on devices with restrictions on access alignments, such as
	66	* /dev/raw, with a 512 byte alignment restriction. This also
	67	* allows the data to be more aligned more strictly than on
	68	* sector boundaries. This is needed for ubd-mmap, which needs
	69	* the data to be page aligned.
	70	* Fixed (finally!) the rounding bug
	71	*/
	72
f2ea3940 PBG	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
1da177e4 LT	82	struct cow_header_v3 {
	83	__u32 magic;
	84	__u32 version;
	85	__u32 mtime;
	86	__u64 size;
	87	__u32 sectorsize;
	88	__u32 alignment;
	89	__u32 cow_format;
	90	char backing_file[PATH_LEN_V3];
cda402b2	91	} __attribute__((packed));
1da177e4	92
f2ea3940 PBG	93	/* This is the broken layout used by some 64-bit binaries. */
	94	struct 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
1da177e4 LT	105	/* COW format definitions - for now, we have only the usual COW bitmap */
	106	#define COW_BITMAP 0
	107
	108	union cow_header {
	109	struct cow_header_v1 v1;
	110	struct cow_header_v2 v2;
	111	struct cow_header_v3 v3;
f2ea3940	112	struct cow_header_v3_broken v3_b;
1da177e4 LT	113	};
	114
	115	#define COW_MAGIC 0x4f4f4f4d /* MOOO */
	116	#define COW_VERSION 3
	117
	118	#define DIV_ROUND(x, len) (((x) + (len) - 1) / (len))
	119	#define ROUND_UP(x, align) DIV_ROUND(x, align) * (align)
	120
	121	void cow_sizes(int version, __u64 size, int sectorsize, int align,
	122	int bitmap_offset, unsigned long *bitmap_len_out,
	123	int *data_offset_out)
	124	{
	125	if(version < 3){
	126	bitmap_len_out = (size + sectorsize - 1) / (8 sectorsize);
	127
	128	data_offset_out = bitmap_offset + bitmap_len_out;
	129	data_offset_out = (data_offset_out + sectorsize - 1) /
	130	sectorsize;
	131	data_offset_out = sectorsize;
	132	}
	133	else {
	134	*bitmap_len_out = DIV_ROUND(size, sectorsize);
	135	bitmap_len_out = DIV_ROUND(bitmap_len_out, 8);
	136
	137	data_offset_out = bitmap_offset + bitmap_len_out;
	138	data_offset_out = ROUND_UP(data_offset_out, align);
	139	}
	140	}
	141
	142	static int absolutize(char to, int size, char from)
	143	{
	144	char save_cwd[256], *slash;
	145	int remaining;
	146
	147	if(getcwd(save_cwd, sizeof(save_cwd)) == NULL) {
	148	cow_printf("absolutize : unable to get cwd - errno = %d\n",
	149	errno);
	150	return(-1);
	151	}
	152	slash = strrchr(from, '/');
	153	if(slash != NULL){
	154	*slash = '\0';
	155	if(chdir(from)){
	156	*slash = '/';
	157	cow_printf("absolutize : Can't cd to '%s' - "
	158	"errno = %d\n", from, errno);
	159	return(-1);
	160	}
	161	*slash = '/';
	162	if(getcwd(to, size) == NULL){
	163	cow_printf("absolutize : unable to get cwd of '%s' - "
	164	"errno = %d\n", from, errno);
	165	return(-1);
	166	}
	167	remaining = size - strlen(to);
	168	if(strlen(slash) + 1 > remaining){
	169	cow_printf("absolutize : unable to fit '%s' into %d "
	170	"chars\n", from, size);
	171	return(-1);
	172	}
	173	strcat(to, slash);
	174	}
	175	else {
	176	if(strlen(save_cwd) + 1 + strlen(from) + 1 > size){
177	cow_printf("absolutize : unable to fit '%s' into %d "
178	"chars\n", from, size);
179	return(-1);
180	}
181	strcpy(to, save_cwd);
182	strcat(to, "/");
183	strcat(to, from);
184	}
185	chdir(save_cwd);
186	return(0);
187	}
188
189	int write_cow_header(char cow_file, int fd, char backing_file,
190	int sectorsize, int alignment, unsigned long long *size)
191	{
192	struct cow_header_v3 *header;
193	unsigned long modtime;
194	int err;
195
196	err = cow_seek_file(fd, 0);
197	if(err < 0){
198	cow_printf("write_cow_header - lseek failed, err = %d\n", -err);
199	goto out;
200	}
201
202	err = -ENOMEM;
203	header = cow_malloc(sizeof(*header));
204	if(header == NULL){
31bc5a33	205	cow_printf("write_cow_header - failed to allocate COW V3 header\n");
1da177e4 LT	206	goto out;
	207	}
	208	header->magic = htonl(COW_MAGIC);
	209	header->version = htonl(COW_VERSION);
	210
	211	err = -EINVAL;
	212	if(strlen(backing_file) > sizeof(header->backing_file) - 1){
	213	cow_printf("Backing file name \"%s\" is too long - names are "
	214	"limited to %d characters\n", backing_file,
	215	sizeof(header->backing_file) - 1);
	216	goto out_free;
	217	}
	218
	219	if(absolutize(header->backing_file, sizeof(header->backing_file),
	220	backing_file))
	221	goto out_free;
	222
	223	err = os_file_modtime(header->backing_file, &modtime);
	224	if(err < 0){
31bc5a33 PBG	225	cow_printf("write_cow_header - backing file '%s' mtime "
	226	"request failed, err = %d\n", header->backing_file,
	227	-err);
1da177e4 LT	228	goto out_free;
	229	}
	230
	231	err = cow_file_size(header->backing_file, size);
	232	if(err < 0){
31bc5a33 PBG	233	cow_printf("write_cow_header - couldn't get size of "
	234	"backing file '%s', err = %d\n",
	235	header->backing_file, -err);
1da177e4 LT	236	goto out_free;
	237	}
	238
	239	header->mtime = htonl(modtime);
	240	header->size = htonll(*size);
	241	header->sectorsize = htonl(sectorsize);
	242	header->alignment = htonl(alignment);
	243	header->cow_format = COW_BITMAP;
	244
31bc5a33	245	err = cow_write_file(fd, header, sizeof(*header));
1da177e4	246	if(err != sizeof(*header)){
31bc5a33 PBG	247	cow_printf("write_cow_header - write of header to "
	248	"new COW file '%s' failed, err = %d\n", cow_file,
	249	-err);
1da177e4 LT	250	goto out_free;
	251	}
	252	err = 0;
	253	out_free:
	254	cow_free(header);
	255	out:
	256	return(err);
	257	}
	258
	259	int file_reader(__u64 offset, char buf, int len, void arg)
	260	{
	261	int fd = ((int ) arg);
	262
	263	return(pread(fd, buf, len, offset));
	264	}
	265
	266	/* XXX Need to sanity-check the values read from the header */
	267
	268	int read_cow_header(int (reader)(__u64, char , int, void ), void arg,
	269	__u32 version_out, char *backing_file_out,
	270	time_t mtime_out, unsigned long long size_out,
	271	int sectorsize_out, __u32 align_out,
	272	int *bitmap_offset_out)
	273	{
	274	union cow_header *header;
	275	char *file;
	276	int err, n;
	277	unsigned long version, magic;
	278
	279	header = cow_malloc(sizeof(*header));
	280	if(header == NULL){
	281	cow_printf("read_cow_header - Failed to allocate header\n");
	282	return(-ENOMEM);
	283	}
	284	err = -EINVAL;
	285	n = (reader)(0, (char ) header, sizeof(*header), arg);
	286	if(n < offsetof(typeof(header->v1), backing_file)){
	287	cow_printf("read_cow_header - short header\n");
	288	goto out;
	289	}
	290
	291	magic = header->v1.magic;
	292	if(magic == COW_MAGIC) {
	293	version = header->v1.version;
	294	}
	295	else if(magic == ntohl(COW_MAGIC)){
	296	version = ntohl(header->v1.version);
	297	}
	298	/* No error printed because the non-COW case comes through here */
	299	else goto out;
	300
	301	*version_out = version;
	302
	303	if(version == 1){
	304	if(n < sizeof(header->v1)){
	305	cow_printf("read_cow_header - failed to read V1 "
	306	"header\n");
	307	goto out;
	308	}
	309	*mtime_out = header->v1.mtime;
	310	*size_out = header->v1.size;
	311	*sectorsize_out = header->v1.sectorsize;
	312	*bitmap_offset_out = sizeof(header->v1);
	313	align_out = sectorsize_out;
314	file = header->v1.backing_file;
315	}
316	else if(version == 2){
317	if(n < sizeof(header->v2)){
318	cow_printf("read_cow_header - failed to read V2 "
319	"header\n");
320	goto out;
321	}
322	*mtime_out = ntohl(header->v2.mtime);
323	*size_out = ntohll(header->v2.size);
324	*sectorsize_out = ntohl(header->v2.sectorsize);
325	*bitmap_offset_out = sizeof(header->v2);
326	align_out = sectorsize_out;
327	file = header->v2.backing_file;
328	}
f2ea3940 PBG	329	/* This is very subtle - see above at union cow_header definition */
f2ea3940 PBG	330	else if(version == 3 && (((int)header->v3.backing_file) != 0)){
1da177e4	331	if(n < sizeof(header->v3)){
31bc5a33	332	cow_printf("read_cow_header - failed to read V3 "
1da177e4 LT	333	"header\n");
	334	goto out;
	335	}
	336	*mtime_out = ntohl(header->v3.mtime);
	337	*size_out = ntohll(header->v3.size);
	338	*sectorsize_out = ntohl(header->v3.sectorsize);
	339	*align_out = ntohl(header->v3.alignment);
f2ea3940 PBG	340	if (*align_out == 0) {
	341	cow_printf("read_cow_header - invalid COW header, "
	342	"align == 0\n");
	343	}
1da177e4 LT	344	bitmap_offset_out = ROUND_UP(sizeof(header->v3), align_out);
	345	file = header->v3.backing_file;
	346	}
f2ea3940 PBG	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	}
1da177e4 LT	377	else {
	378	cow_printf("read_cow_header - invalid COW version\n");
	379	goto out;
	380	}
	381	err = -ENOMEM;
	382	*backing_file_out = cow_strdup(file);
	383	if(*backing_file_out == NULL){
	384	cow_printf("read_cow_header - failed to allocate backing "
	385	"file\n");
	386	goto out;
	387	}
	388	err = 0;
	389	out:
	390	cow_free(header);
	391	return(err);
	392	}
	393
	394	int init_cow_file(int fd, char cow_file, char backing_file, int sectorsize,
	395	int alignment, int *bitmap_offset_out,
	396	unsigned long bitmap_len_out, int data_offset_out)
	397	{
	398	unsigned long long size, offset;
	399	char zero = 0;
	400	int err;
	401
	402	err = write_cow_header(cow_file, fd, backing_file, sectorsize,
	403	alignment, &size);
	404	if(err)
	405	goto out;
	406
	407	*bitmap_offset_out = ROUND_UP(sizeof(struct cow_header_v3), alignment);
	408	cow_sizes(COW_VERSION, size, sectorsize, alignment, *bitmap_offset_out,
	409	bitmap_len_out, data_offset_out);
	410
	411	offset = *data_offset_out + size - sizeof(zero);
	412	err = cow_seek_file(fd, offset);
	413	if(err < 0){
	414	cow_printf("cow bitmap lseek failed : err = %d\n", -err);
	415	goto out;
	416	}
	417
	418	/* does not really matter how much we write it is just to set EOF
	419	* this also sets the entire COW bitmap
	420	* to zero without having to allocate it
	421	*/
	422	err = cow_write_file(fd, &zero, sizeof(zero));
	423	if(err != sizeof(zero)){
	424	cow_printf("Write of bitmap to new COW file '%s' failed, "
	425	"err = %d\n", cow_file, -err);
fe1db50c PBG	426	if (err >= 0)
fe1db50c PBG	427	err = -EINVAL;
1da177e4 LT	428	goto out;
	429	}
	430
	431	return(0);
	432
	433	out:
	434	return(err);
	435	}
	436
	437	/*
	438	* ---------------------------------------------------------------------------
	439	* Local variables:
	440	* c-file-style: "linux"
	441	* End:
	442	*/