File initvm.c of Package build
/*
* NAME
* initvm - init for qemu, setup binfmt_misc launch build
*
* SYNOPSIS
* initvm
*
* DESCRIPTION
* This is the kernel init script for virtual machines which will
* be running executables for an embedded (non-native)
* architecture. It registers binfmt_misc handlers for qemu and
* executes the build script, and tests many assumptions.
*
* FILES
* /.build/qemu-reg
* text file with lines to stuff into the binfmt_misc
* filesystem registration file
* /.build/build
* build script to execute once binfmts are set up
*
* AUTHOR
* Copyright (c) 2012 James Perkins <james.perkins@linuxfoundation.org>
* Adrian Schroeter <adrian@suse.de>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 or 3 as
* published by the Free Software Foundation.
*
* 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program (see the file COPYING); if not, write to the
* Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA
*/
#include <sys/mount.h>
#include <sys/stat.h>
#include <sys/utsname.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <stdio.h>
#include <unistd.h>
/* to enable debugging, compile with -DDEBUG */
#ifdef DEBUG
#define DBG(x) do { x; } while(0)
#else
#define DBG(x)
#endif
/* function return codes */
enum okfail { FAIL=0, OK=1 };
/* qemu registration fields, see kernel/Documentation/binfmt_misc.txt */
enum fields { ignore=0, name, type, offset, magic, mask, interpreter, flags };
const char * const fieldnames[] = {
"ignore", "name", "type", "offset",
"magic", "mask", "interpreter", "flags"
};
const int n_fields = 8;
/* files in useful places */
#define SYSFS_BINFMT_MISC "/proc/sys/fs/binfmt_misc"
#define SYSFS_BINFMT_MISC_REG "/proc/sys/fs/binfmt_misc/register"
#define SYSFS_BINFMT_MISC_STAT "/proc/sys/fs/binfmt_misc/status"
/* /usr/lib/build/x paths are copied to /.build inside a virtual machine */
#define BINFMT_REGF_0 "/.build/qemu-reg"
#define BINFMT_REGF_1 "/usr/lib/build/qemu-reg"
#define BUILD "/.build/build"
/* useful constant arrays */
static char *rx_files[] = { "/proc", "/proc/sys", "/proc/sys/fs",
SYSFS_BINFMT_MISC, NULL };
static char *w_files[] = { SYSFS_BINFMT_MISC_REG, NULL };
static char* const args[] = { BUILD, NULL };
/* test access modes for files, return OK or FAIL */
enum okfail test_access_files(char *files[], int mode, const char *errstr)
{
int i;
for (i = 0; files[i] != NULL; i++) {
if (access(files[i], mode) != 0) {
fprintf(stderr, "%s: %s: fails test\n",
files[i], errstr);
return FAIL;
}
}
return OK;
}
/* find a string in the given file, return OK or FAIL */
enum okfail strfile(const char *filename, const char *string)
{
char buf[BUFSIZ];
FILE *fp;
enum okfail found = FAIL;
fp = fopen(filename, "r");
if (fp == NULL)
{
perror(filename);
return FAIL;
}
while (fgets(buf, sizeof(buf), fp) != NULL)
{
if (strcmp(buf, string) == 0) {
found = OK;
break;
}
}
(void)fclose(fp);
return found;
}
/* write the file with given string, return OK or FAIL */
enum okfail write_file_string(const char *filename, const char *string)
{
int fd;
if ((fd = open(filename, O_WRONLY)) == -1)
{
perror(filename);
return FAIL;
}
if (write(fd, string, strlen(string)) == -1)
{
perror("write");
fprintf(stderr, "%s: write failed\n", filename);
close(fd);
return FAIL;
}
close(fd);
return OK;
}
#ifdef DEBUG
/* dump contents of the file to stderr, return OK or FAIL */
enum okfail dump_file(char *path)
{
FILE *fp;
char buf[BUFSIZ];
fp = fopen(path, "r");
if (fp == NULL) {
perror(path);
return FAIL;
}
while (fgets(buf, sizeof(buf), fp) != NULL)
{
fputs(buf, stderr);
}
fclose(fp);
return OK;
}
#endif /* DEBUG */
/* parse datafile and register (to regfile) all binary formats found */
enum okfail binfmt_register(char *datafile, char *regfile)
{
char buf[BUFSIZ + 7]; /* extra room for -binfmt */
FILE *fp;
int line;
struct utsname myuname;
uname(&myuname);
fp = fopen(datafile, "r");
if (fp == NULL)
{
perror(datafile);
return FAIL;
}
for (line = 1; fgets(buf, sizeof(buf) - 7, fp) != NULL; line++)
{
char tokens[BUFSIZ];
char *s = tokens;
char *blacklist;
char *f[n_fields]; /* field content pointers */
int n; /* current field */
char path[BUFSIZ];
if (buf[0] != ':') /* non-data input line */
{
continue;
}
blacklist = strchr(buf, ' ');
if (blacklist) {
int skip = 0;
char *eol;
*blacklist = '\0';
blacklist++;
eol = strchr(blacklist, '\n');
if (eol)
*eol = '\0';
for (n = 0; blacklist != NULL; n++)
{
char *bp = strsep(&blacklist, " ");
if (!strcmp(bp, myuname.machine)) {
#ifdef DEBUG
fprintf(stderr, " skipping on hostarch %s line %s\n", bp, buf);
#endif /* DEBUG */
skip = 1;
break;
}
}
if (skip)
continue;
}
/* copy buf and tokenize :-seperated fields into f[] */
strcpy(tokens, buf);
for (n = 0; s != NULL && n < n_fields; n++)
{
f[n] = strsep(&s, ":");
}
#ifdef DEBUG
int i;
fprintf(stderr, "DEBUG: line %d, fields %d:\n", line, n);
for (i = name; i < n; i++)
{
fprintf(stderr, " %s %s\n", fieldnames[i], f[i]);
}
#endif /* DEBUG */
if (n == n_fields && s != NULL)
{
fprintf(stderr, "%s: line %d: extra fields, ignoring."
" Content: %s", datafile, line, buf);
continue;
}
if (n < n_fields)
{
fprintf(stderr, "%s: line %d: missing fields, ignoring."
" Content: %s", datafile, line, buf);
continue;
}
int ret;
/* Is an interpreter for this arch already registered? */
snprintf(path, sizeof(path), SYSFS_BINFMT_MISC "/%s", f[name]);
ret=access(path, X_OK);
if (ret == 0) {
#ifdef DEBUG
fprintf(stderr,
"interpreter for '%s' already registered, ignoring\n",
f[name]);
#endif /* DEBUG */
continue;
}
#ifdef DEBUG
fprintf(stderr,
"registering interpreter for '%s'...\n",
f[name]);
#endif /* DEBUG */
/* check if a special -binfmt interpreter version exists */
snprintf(path, sizeof(path), "%s-binfmt", f[interpreter]);
ret=access(path, X_OK);
if (ret == 0) {
/* special -binfmt interpreter exists, patch buf */
size_t off = f[interpreter] + strlen(f[interpreter]) - tokens;
size_t len = strlen(buf) + 1;
memmove(buf + off + 7, buf + off, len - off);
memcpy(buf + off, "-binfmt", 7);
} else {
/* Does the interpreter exists? */
ret=access(f[interpreter], X_OK);
}
if (ret != 0) {
#ifdef DEBUG
fprintf(stderr,
"%s: line %d: interpreter '%s' not found,"
" ignoring, return %d\n", datafile, line, f[interpreter], ret);
#endif /* DEBUG */
continue;
}
if (!write_file_string(regfile, buf)) {
fprintf(stderr, "%s: line %d: write failed."
" Content: %s\n", datafile, line, buf);
(void)fclose(fp);
return FAIL;
}
/* verify registration completed correctly */
snprintf(path, sizeof(path), SYSFS_BINFMT_MISC "/%s", f[name]);
if (access(path, R_OK) != 0) {
fprintf(stderr,
"%s: line %d: binfmt path not created, content '%s'\n",
path, line, buf);
(void)fclose(fp);
return FAIL;
}
DBG(fprintf(stderr, "dumping: %s\n", path));
DBG(dump_file(path));
}
(void)fclose(fp);
return OK;
}
/* set up/verify binfmt FS support, program more binfmts, and launch build */
int main(int argc, char* argv[], char* env[])
{
int retval;
char buf[BUFSIZ], *build_dir;
/* Docker builds get /proc mounted */
struct stat sb;
if (stat("/.dockerenv", &sb)) {
/* mount proc filesystem if it isn't already. */
if (mount("proc", "/proc", "proc", MS_MGC_VAL, NULL) == -1) {
if (errno != EBUSY) {
perror("mount: /proc");
exit(1);
}
}
}
/* Docker builds need to have binfmt_misc loaded already */
if (stat(SYSFS_BINFMT_MISC_STAT, &sb)) {
/* try to load binfmt module if present, no big deal if it fails */
if ((retval = system("/sbin/modprobe binfmt_misc")) != 0) {
DBG(fprintf(stderr, "modprobe binfmt_misc exit code %d\n",
retval));
}
/* mount binfmt filesystem */
if (mount("binfmt_misc", SYSFS_BINFMT_MISC, "binfmt_misc", MS_MGC_VAL,
NULL) == -1) {
if (errno != EBUSY) {
perror("mount: binfmt_misc, " SYSFS_BINFMT_MISC);
}
}
}
/* verify all paths resulting from this are OK */
if (!test_access_files(rx_files, R_OK|X_OK, "read/search")) {
exit(1);
}
if (!test_access_files(w_files, W_OK, "write")) {
exit(1);
}
if (!strfile("/proc/filesystems", "nodev\tbinfmt_misc\n")) {
fprintf(stderr,
"/proc/filesystems: binfmt_misc support missing\n");
exit(1);
}
if (!strfile(SYSFS_BINFMT_MISC_STAT, "enabled\n")) {
fprintf(stderr,
"%s: binfmt_misc filesystem support not enabled\n",
SYSFS_BINFMT_MISC_STAT);
exit(1);
}
*buf = 0;
build_dir = getenv("BUILD_DIR");
if (build_dir && strlen(build_dir) < sizeof(buf) - 10)
sprintf(buf, "%s/qemu-reg", build_dir);
if (!*buf || !binfmt_register(buf, SYSFS_BINFMT_MISC_REG)) {
/* setup all done, do the registration */
if (!binfmt_register(BINFMT_REGF_0, SYSFS_BINFMT_MISC_REG)) {
fprintf(stderr, "%s: failed. Trying alternate binfmt file\n",
BINFMT_REGF_0);
if (!binfmt_register(BINFMT_REGF_1, SYSFS_BINFMT_MISC_REG)) {
fprintf(stderr, "%s: binfmt registration failed\n",
BINFMT_REGF_1);
exit(1);
}
}
}
/* if we are the init process, start build */
if (getpid() == 1)
{
if (access(BUILD, F_OK) != 0) {
fprintf(stderr, "%s: build executable missing\n",
BUILD);
exit(1);
}
if (access(BUILD, X_OK) != 0) {
fprintf(stderr, "%s: not executable\n", BUILD);
exit(1);
}
execve(BUILD, args, env);
perror("execve of "BUILD);
exit(1);
}
/* success! */
exit(0);
}
