root/usr/gen_init_cpio.c

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <string.h>
#include <unistd.h>
#include <time.h>
#include <fcntl.h>

static unsigned int offset;
static unsigned int ino = 721;

static void push_string(const char *name)
{
        unsigned int name_len = strlen(name) + 1;

        fputs(name, stdout);
        putchar(0);
        offset += name_len;
}

static void push_pad (void)
{
        while (offset & 3) {
                putchar(0);
                offset++;
        }
}

static void push_rest(const char *name)
{
        unsigned int name_len = strlen(name) + 1;
        unsigned int tmp_ofs;

        fputs(name, stdout);
        putchar(0);
        offset += name_len;

        tmp_ofs = name_len + 110;
        while (tmp_ofs & 3) {
                putchar(0);
                offset++;
                tmp_ofs++;
        }
}

static void push_hdr(const char *s)
{
        fputs(s, stdout);
        offset += 110;
}

static void cpio_trailer(void)
{
        char s[256];
        const char name[] = "TRAILER!!!";

        sprintf(s, "%s%08X%08X%08lX%08lX%08X%08lX"
               "%08X%08X%08X%08X%08X%08X%08X",
                "070701",               /* magic */
                0,                      /* ino */
                0,                      /* mode */
                (long) 0,               /* uid */
                (long) 0,               /* gid */
                1,                      /* nlink */
                (long) 0,               /* mtime */
                0,                      /* filesize */
                0,                      /* major */
                0,                      /* minor */
                0,                      /* rmajor */
                0,                      /* rminor */
                (unsigned)strlen(name) + 1, /* namesize */
                0);                     /* chksum */
        push_hdr(s);
        push_rest(name);

        while (offset % 512) {
                putchar(0);
                offset++;
        }
}

static void cpio_mkdir(const char *name, unsigned int mode,
                       uid_t uid, gid_t gid)
{
        char s[256];
        time_t mtime = time(NULL);

        sprintf(s,"%s%08X%08X%08lX%08lX%08X%08lX"
               "%08X%08X%08X%08X%08X%08X%08X",
                "070701",               /* magic */
                ino++,                  /* ino */
                S_IFDIR | mode,         /* mode */
                (long) uid,             /* uid */
                (long) gid,             /* gid */
                2,                      /* nlink */
                (long) mtime,           /* mtime */
                0,                      /* filesize */
                3,                      /* major */
                1,                      /* minor */
                0,                      /* rmajor */
                0,                      /* rminor */
                (unsigned)strlen(name) + 1,/* namesize */
                0);                     /* chksum */
        push_hdr(s);
        push_rest(name);
}

static void cpio_mknod(const char *name, unsigned int mode,
                       uid_t uid, gid_t gid, int dev_type,
                       unsigned int maj, unsigned int min)
{
        char s[256];
        time_t mtime = time(NULL);

        if (dev_type == 'b')
                mode |= S_IFBLK;
        else
                mode |= S_IFCHR;

        sprintf(s,"%s%08X%08X%08lX%08lX%08X%08lX"
               "%08X%08X%08X%08X%08X%08X%08X",
                "070701",               /* magic */
                ino++,                  /* ino */
                mode,                   /* mode */
                (long) uid,             /* uid */
                (long) gid,             /* gid */
                1,                      /* nlink */
                (long) mtime,           /* mtime */
                0,                      /* filesize */
                3,                      /* major */
                1,                      /* minor */
                maj,                    /* rmajor */
                min,                    /* rminor */
                (unsigned)strlen(name) + 1,/* namesize */
                0);                     /* chksum */
        push_hdr(s);
        push_rest(name);
}

/* Not marked static to keep the compiler quiet, as no one uses this yet... */
void cpio_mkfile(const char *filename, const char *location,
                        unsigned int mode, uid_t uid, gid_t gid)
{
        char s[256];
        char *filebuf;
        struct stat buf;
        int file;
        int retval;
        int i;

        mode |= S_IFREG;

        retval = stat (filename, &buf);
        if (retval) {
                fprintf (stderr, "Filename %s could not be located\n", filename);
                goto error;
        }

        file = open (filename, O_RDONLY);
        if (file < 0) {
                fprintf (stderr, "Filename %s could not be opened for reading\n", filename);
                goto error;
        }

        filebuf = malloc(buf.st_size);
        if (!filebuf) {
                fprintf (stderr, "out of memory\n");
                goto error_close;
        }

        retval = read (file, filebuf, buf.st_size);
        if (retval < 0) {
                fprintf (stderr, "Can not read %s file\n", filename);
                goto error_free;
        }

        sprintf(s,"%s%08X%08X%08lX%08lX%08X%08lX"
               "%08X%08X%08X%08X%08X%08X%08X",
                "070701",               /* magic */
                ino++,                  /* ino */
                mode,                   /* mode */
                (long) uid,             /* uid */
                (long) gid,             /* gid */
                1,                      /* nlink */
                (long) buf.st_mtime,    /* mtime */
                (int) buf.st_size,      /* filesize */
                3,                      /* major */
                1,                      /* minor */
                0,                      /* rmajor */
                0,                      /* rminor */
                (unsigned)strlen(location) + 1,/* namesize */
                0);                     /* chksum */
        push_hdr(s);
        push_string(location);
        push_pad();

        for (i = 0; i < buf.st_size; ++i)
                fputc(filebuf[i], stdout);
        offset += buf.st_size;
        close(file);
        free(filebuf);
        push_pad();
        return;
        
error_free:
        free(filebuf);
error_close:
        close(file);
error:
        exit(-1);
}

int main (int argc, char *argv[])
{
        cpio_mkdir("/dev", 0755, 0, 0);
        cpio_mknod("/dev/console", 0600, 0, 0, 'c', 5, 1);
        cpio_mkdir("/root", 0700, 0, 0);
        cpio_trailer();

        exit(0);

        /* silence compiler warnings */
        return 0;
        (void) argc;
        (void) argv;
}