From 2f957068e567391e7aef5d7a2c075c14c1e6b37a Mon Sep 17 00:00:00 2001
From: turret <turret@duck.com>
Date: Fri, 24 Nov 2023 00:57:35 -0600
Subject: misc: subsys upgrade, log timestamps

(log)
 - create LOGLEVEL constant numbers
 - implement CONSOLE_LOGLEVEL
 - color array now uses loglevel constants
 - timestamp now shown (thanks util-linux)
(init)
 - register mainpid
 - hello world print
 - fix process reaper to refer to subsys when reaping
(subsys)
 - create maximum subsystem count
 - create subsystem table
 - add debugging prints to subsystem entry and termination
 - create function to handle process termination (unmap stack, free
   subsystem malloc, clear entry in table)
 - disable subsystem inception
 - change die references to fail with print
 - supply clone with signal to send on termination (SIGCHLD)
---
 init/subsys.c | 66 +++++++++++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 58 insertions(+), 8 deletions(-)

(limited to 'init/subsys.c')

diff --git a/init/subsys.c b/init/subsys.c
index 62ee54e..a88046d 100644
--- a/init/subsys.c
+++ b/init/subsys.c
@@ -1,5 +1,6 @@
 #include <errno.h>
 #include <sched.h>
+#include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -13,13 +14,20 @@
 #include <util.h>
 
 #define STACK_SIZE 8192 * 512
+#define MAX_SUBSYSTEMS 32
 
 struct subsystem_info {
     char *fn_name;
     int (*fn)(void);
+    int pid;
+    void *stack;
 };
 
-int __subsystem_entry(struct subsystem_info *info)
+extern int mainpid;
+static struct subsystem_info *subsystems[MAX_SUBSYSTEMS + 1];
+static int subsystem_count = 0;
+
+static 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
@@ -30,21 +38,51 @@ int __subsystem_entry(struct subsystem_info *info)
     prctl(PR_SET_NAME, name);
     free(name);
 
-    int ret = info->fn();
+    print(LOG_DEBUG "subsys: starting subsystem %s (%d)", info->fn_name, getpid());
 
-    /* we are expected to free info before  exiting */
-    free(info);
+    int ret = info->fn();
 
     return ret;
 }
 
+int subsystem_handle_term(int pid)
+{
+    for(int i = 0; i < MAX_SUBSYSTEMS; ++i) {
+        struct subsystem_info *subsystem = subsystems[i];
+        if(!subsystem || subsystem->pid != pid)
+            continue;
+
+        print(LOG_DEBUG "subsys: subsystem terminated %s (%d)", subsystem->fn_name, pid);
+
+        if(munmap(subsystem->stack, STACK_SIZE) < 0)
+            print(LOG_EMERG "subsys: failed to deallocate stack for subsystem %s (%d) (errno %d)", subsystem->fn_name, pid, errno);
+        subsystems[i] = 0;
+        free(subsystem);
+
+        return 0;
+    }
+
+    return 1;
+}
+
 int __impl_start_subsystem(char *fn_name, int (*fn)(void))
 {
+    if(getpid() != mainpid) {
+        print(LOG_CRIT "subsys: cannot perform subsystem inception (attempted from %d)", getpid());
+        return 1;
+    }
+    if(subsystem_count >= MAX_SUBSYSTEMS) {
+        print(LOG_CRIT "subsys: cannot start subsystem %s: reached maximum number of subsystems", fn_name);
+        return 1;
+    }
+
     /* 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:");
+    if((long)stack <= 0) {
+        print(LOG_CRIT "subsys: cannot start subsystem %s: failed to allocate stack (errno %d)", fn_name, errno);
+        return 1;
+    }
 
     /* 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
@@ -52,11 +90,23 @@ int __impl_start_subsystem(char *fn_name, int (*fn)(void))
     struct subsystem_info *info = malloc(sizeof(struct subsystem_info));
     info->fn_name = fn_name;
     info->fn = fn;
+    info->stack = stack;
 
-    int pid = clone((int (*)(void *))__subsystem_entry, (void *)((long)stack + STACK_SIZE), CLONE_FILES | CLONE_VM, info);
+    int pid = clone((int (*)(void *))__subsystem_entry, (void *)((long)stack + STACK_SIZE), CLONE_FILES | CLONE_VM | SIGCHLD, info);
+    info->pid = pid;
     if(pid < 0) {
+        print(LOG_CRIT "subsys: cannot start subsystem %s: clone failed (errno %d)", fn_name, errno);
         munmap(stack, STACK_SIZE);
-        die("subsys clone:");
+        free(info);
+        return 1;
+    }
+
+    for(int i = 0; i < MAX_SUBSYSTEMS; ++i) {
+        if(!subsystems[i]) {
+            subsystems[i] = info;
+            ++subsystem_count;
+            break;
+        }
     }
 
     return 0;
-- 
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