source: bootcd/isolinux/syslinux-6.03/com32/libupload/cpio.c

/*
 * cpio.c
 *
 * Write a compressed CPIO file
 */

#include <stdio.h>
#include <string.h>
#include <inttypes.h>
#include <stdbool.h>
#include <zlib.h>
#include "upload_backend.h"
#include "ctime.h"

int cpio_pad(struct upload_backend *be)
{
    static char pad[4];         /* Up to 4 zero bytes */
    if (be->dbytes & 3)
        return write_data(be, pad, -be->dbytes & 3);
    else
        return 0;
}

int cpio_hdr(struct upload_backend *be, uint32_t mode, size_t datalen,
             const char *filename)
{
    static uint32_t inode = 2;
    char hdr[6+13*8+1];
    int nlen = strlen(filename)+1;
    int rv = 0;

    cpio_pad(be);

    sprintf(hdr, "%06o%08x%08x%08x%08x%08x%08x%08zx%08x%08x%08x%08x%08x%08x",
            070701,             /* c_magic */
            inode++,            /* c_ino */
            mode,               /* c_mode */
            0,                  /* c_uid */
            0,                  /* c_gid */
            1,                  /* c_nlink */
            be->now,            /* c_mtime */
            datalen,            /* c_filesize */
            0,                  /* c_maj */
            0,                  /* c_min */
            0,                  /* c_rmaj */
            0,                  /* c_rmin */
            nlen,               /* c_namesize */
            0);                 /* c_chksum */
    rv |= write_data(be, hdr, 6+13*8);
    rv |= write_data(be, filename, nlen);
    rv |= cpio_pad(be);
    return rv;
}

int cpio_mkdir(struct upload_backend *be, const char *filename)
{
    return cpio_hdr(be, MODE_DIR, 0, filename);
}

int cpio_writefile(struct upload_backend *be, const char *filename,
                   const void *data, size_t len)
{
    int rv;

    rv = cpio_hdr(be, MODE_FILE, len, filename);
    rv |= write_data(be, data, len);
    rv |= cpio_pad(be);

    return rv;
}

int cpio_close(struct upload_backend *be)
{
    return cpio_hdr(be, 0, 0, "TRAILER!!!");
}