// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (C) 2007 Jeff Dike (jdike@{linux.intel,addtoit}.com)
*/
/*
* _XOPEN_SOURCE is needed for pread, but we define _GNU_SOURCE, which defines
* that.
*/
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <arpa/inet.h>
#include <endian.h>
#include "cow.h"
#include "cow_sys.h"
#define PATH_LEN_V1 256
/* unsigned time_t works until year 2106 */
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);
}
if (chdir(save_cwd)) {
cow_printf("absolutize : Can't cd to '%s' - "
"errno = %d\n", save_cwd, errno);
return -1;
}
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;
long 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 = htobe32(COW_MAGIC);
header->version = htobe32(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 = htobe32(modtime);
header->size = htobe64(*size);
header->sectorsize = htobe32(sectorsize);
header->alignment = htobe32(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,
long long *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 == be32toh(COW_MAGIC))
version = be32toh(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 = be32toh(header->v2.mtime);
*size_out = be64toh(header->v2.size);
*sectorsize_out = be32toh(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 = be32toh(header->v3.mtime);
*size_out = be64toh(header->v3.size);
*sectorsize_out = be32toh(header->v3.sectorsize);
*align_out = be32toh(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
* 2106+. I.e. we can safely do this truncating cast.
*
* Additionally, we must use be32toh() instead of be64toh(), 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) be32toh(header->v3_b.mtime);
*size_out = be64toh(header->v3_b.size);
*sectorsize_out = be32toh(header->v3_b.sectorsize);
*align_out = be32toh(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;
}