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/* skipcpio.c
Copyright (C) 2012 Harald Hoyer
Copyright (C) 2012 Red Hat, Inc. All rights reserved.
This program is free software: you can redistribute it and/or modify
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with this program; If not, see <http://www.gnu.org/licenses/>.
*/
#define PROGRAM_VERSION_STRING "1"
#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define CPIO_MAGIC "070701"
#define CPIO_MAGIC_LEN (sizeof(CPIO_MAGIC) - 1)
#define CPIO_END "TRAILER!!!"
#define CPIO_ENDLEN (sizeof(CPIO_END) - 1)
#define CPIO_ALIGNMENT 4
#define ALIGN_UP(n, a) (((n) + (a) - 1) & (~((a) - 1)))
#define pr_err(fmt, ...) \
fprintf(stderr, "ERROR: %s:%d:%s(): " fmt, __FILE__, __LINE__, \
__func__, ##__VA_ARGS__)
struct cpio_header {
char c_magic[CPIO_MAGIC_LEN];
char c_ino[8];
char c_mode[8];
char c_uid[8];
char c_gid[8];
char c_nlink[8];
char c_mtime[8];
char c_filesize[8];
char c_dev_maj[8];
char c_dev_min[8];
char c_rdev_maj[8];
char c_rdev_min[8];
char c_namesize[8];
char c_chksum[8];
} __attribute__((packed));
struct buf_struct {
struct cpio_header h;
char filename[CPIO_ENDLEN];
} __attribute__((packed));
union buf_union {
struct buf_struct cpio;
char copy_buffer[2048];
};
static union buf_union buf;
int main(int argc, char **argv)
{
size_t s;
long pos = 0;
FILE *f = NULL;
char *fname = NULL;
int ret = EXIT_FAILURE;
unsigned long filesize;
unsigned long filename_length;
if (argc != 2) {
fprintf(stderr, "Usage: %s <file>\n", argv[0]);
goto end;
}
fname = argv[1];
f = fopen(fname, "r");
if (f == NULL) {
pr_err("Cannot open file '%s'\n", fname);
goto end;
}
if ((fread(&buf.cpio, sizeof(buf.cpio), 1, f) != 1) ||
ferror(f)) {
pr_err("Read error from file '%s'\n", fname);
goto end;
}
if (fseek(f, 0, SEEK_SET)) {
pr_err("fseek error on file '%s'\n", fname);
goto end;
}
/* check, if this is a cpio archive */
if (memcmp(buf.cpio.h.c_magic, CPIO_MAGIC, CPIO_MAGIC_LEN)) {
goto cat_rest;
}
do {
// zero string, spilling into next unused field, to use strtol
buf.cpio.h.c_chksum[0] = 0;
filename_length = strtoul(buf.cpio.h.c_namesize, NULL, 16);
pos = ALIGN_UP(pos + sizeof(struct cpio_header) + filename_length, CPIO_ALIGNMENT);
// zero string, spilling into next unused field, to use strtol
buf.cpio.h.c_dev_maj[0] = 0;
filesize = strtoul(buf.cpio.h.c_filesize, NULL, 16);
pos = ALIGN_UP(pos + filesize, CPIO_ALIGNMENT);
if (filename_length == (CPIO_ENDLEN + 1)
&& strncmp(buf.cpio.filename, CPIO_END, CPIO_ENDLEN) == 0) {
if (fseek(f, pos, SEEK_SET)) {
pr_err("fseek\n");
goto end;
}
break;
}
if (fseek(f, pos, SEEK_SET)) {
pr_err("fseek\n");
goto end;
}
if ((fread(&buf.cpio, sizeof(buf.cpio), 1, f) != 1) ||
ferror(f)) {
pr_err("fread\n");
goto end;
}
if (memcmp(buf.cpio.h.c_magic, CPIO_MAGIC, CPIO_MAGIC_LEN)) {
pr_err("Corrupt CPIO archive!\n");
goto end;
}
} while (!feof(f));
if (feof(f)) {
/* CPIO_END not found, just cat the whole file */
if (fseek(f, 0, SEEK_SET)) {
pr_err("fseek\n");
goto end;
}
} else {
/* skip zeros */
do {
size_t i;
s = fread(buf.copy_buffer, 1, sizeof(buf.copy_buffer) - 1, f);
if (ferror(f)) {
pr_err("fread\n");
goto end;
}
for (i = 0; (i < s) && (buf.copy_buffer[i] == 0); i++) ;
if (buf.copy_buffer[i]) {
pos += i;
if (fseek(f, pos, SEEK_SET)) {
pr_err("fseek\n");
goto end;
}
break;
}
pos += s;
} while (!feof(f));
}
cat_rest:
/* cat out the rest */
while (!feof(f)) {
s = fread(buf.copy_buffer, 1, sizeof(buf.copy_buffer), f);
if (ferror(f)) {
pr_err("fread\n");
goto end;
}
errno = 0;
if (fwrite(buf.copy_buffer, 1, s, stdout) != s) {
if (errno != EPIPE)
pr_err("fwrite\n");
goto end;
}
}
ret = EXIT_SUCCESS;
end:
if (f) {
fclose(f);
}
return ret;
}
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