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#include <errno.h>
#include <sched.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/prctl.h>
#include <sys/syscall.h>
#include <sys/mman.h>
#include <unistd.h>
#include <config.h>
#include <log.h>
#include <util.h>
#define STACK_SIZE 8192 * 512
struct subsystem_info {
char *fn_name;
int (*fn)(void);
};
int __subsystem_entry(struct subsystem_info *info)
{
/* entry point from clone(). we setup the process name so we know
what we are looking at from a glance in a ps view or htop or
whatever. */
char *name = malloc(16 * sizeof(char));
snprintf(name, 16, NAME_SHORTHAND ": %s", info->fn_name);
name[15] = '\0';
prctl(PR_SET_NAME, name);
free(name);
int ret = info->fn();
/* we are expected to free info before exiting */
free(info);
return ret;
}
int __impl_start_subsystem(char *fn_name, int (*fn)(void))
{
/* because CLONE_VM is being set, our stack is not duplicated and
therefore we need to map a stack */
void *stack = mmap(NULL, STACK_SIZE, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_GROWSDOWN | MAP_STACK | MAP_PRIVATE, -1, 0);
if((long)stack < 0)
die("subsys mmap:");
/* the libc gods have graced us with the ability to pass one (1) arg
to the function. struct required. the absence of a free is not a
memory leak because we free it above. */
struct subsystem_info *info = malloc(sizeof(struct subsystem_info));
info->fn_name = fn_name;
info->fn = fn;
int pid = clone((int (*)(void *))__subsystem_entry, (void *)((long)stack + STACK_SIZE), CLONE_FILES | CLONE_VM, info);
if(pid < 0) {
munmap(stack, STACK_SIZE);
die("subsys clone:");
}
return 0;
}
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