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survive bereaving #141

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survive bereaving #141

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95 changes: 78 additions & 17 deletions dumb-init.c
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,8 @@
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <dirent.h>
#include <ctype.h>
#include "VERSION.h"

#define PRINTERR(...) do { \
Expand All @@ -42,6 +44,7 @@ int signal_rewrite[MAXSIG + 1] = {[0 ... MAXSIG] = -1};
pid_t child_pid = -1;
char debug = 0;
char use_setsid = 1;
static char survive_bereaving = 0;

int translate_signal(int signum) {
if (signum <= 0 || signum > MAXSIG) {
Expand All @@ -67,6 +70,43 @@ void forward_signal(int signum) {
}
}

/*
* Read /proc and see if there are processes except init(PIDs)
*/
signed int process_count() {
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Since this isn't exactly returning the total process count, maybe it'd be better to rename this function to is_only_process_running?

DIR *dp;
struct dirent *ep;
char nonnumber;
signed int count = 0;

dp = opendir ("/proc");
if (dp != NULL)
{
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nit: formatting...

while ((ep = readdir (dp)) != NULL) {
nonnumber = 0;
for (int i = 0; ep->d_name[i] != 0; ++i) {
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nit: I think it'd be slightly more clear to write ep->d_name[i] != '\0'

if (!isdigit(ep->d_name[i])) {
nonnumber = 1;
break;
}
}
if (!nonnumber) {
DEBUG("/proc/%s is a process\n", ep->d_name);
++count;
if (count > 1) {
closedir(dp);
return 2; //2 is enough, do not count further
}
}
}
closedir(dp);
} else {
PRINTERR("Could not open /proc.\n");
return -1;
}
return count;
}

/*
* The dumb-init signal handler.
*
Expand All @@ -88,6 +128,7 @@ void forward_signal(int signum) {
*
*/
void handle_signal(int signum) {
static char bereaved = 0;
DEBUG("Received signal %d.\n", signum);
if (signum == SIGCHLD) {
int status, exit_status;
Expand All @@ -103,11 +144,26 @@ void handle_signal(int signum) {
}

if (killed_pid == child_pid) {
forward_signal(SIGTERM); // send SIGTERM to any remaining children
DEBUG("Child exited with status %d. Goodbye.\n", exit_status);
bereaved = 1;
if (!survive_bereaving) {
forward_signal(SIGTERM); // send SIGTERM to any remaining children
DEBUG("Child exited with status %d. Goodbye.\n", exit_status);
exit(exit_status);
} else {
DEBUG("Child exited with status %d. Stay alive for your grandchildren.\n", exit_status);
}
}
}

if ((bereaved == 1) && survive_bereaving) {
signed int pc = process_count();
DEBUG("Process count: %d\n", pc);
if (pc <= 1) {
DEBUG("No process left, exitting.\n");
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nit: typo exitting -> exiting

exit(exit_status);
}
}

} else {
forward_signal(signum);
if (signum == SIGTSTP || signum == SIGTTOU || signum == SIGTTIN) {
Expand All @@ -126,15 +182,16 @@ void print_help(char *argv[]) {
"It is designed to run as PID1 in minimal container environments.\n"
"\n"
"Optional arguments:\n"
" -c, --single-child Run in single-child mode.\n"
" In this mode, signals are only proxied to the\n"
" direct child and not any of its descendants.\n"
" -r, --rewrite s:r Rewrite received signal s to new signal r before proxying.\n"
" To ignore (not proxy) a signal, rewrite it to 0.\n"
" This option can be specified multiple times.\n"
" -v, --verbose Print debugging information to stderr.\n"
" -h, --help Print this help message and exit.\n"
" -V, --version Print the current version and exit.\n"
" -c, --single-child Run in single-child mode.\n"
" In this mode, signals are only proxied to the\n"
" direct child and not any of its descendants.\n"
" -b, --survive-bereaving Do not quit when the direct child dies.\n"
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I think it'd be helpful to add another line to clarify further when it actually does quit. Maybe a line like "In this mode, dumb-init will quit when there are no other processes running on the host. This mode requires dumb-init to be running as PID 1."?

" -r, --rewrite s:r Rewrite received signal s to new signal r before proxying.\n"
" To ignore (not proxy) a signal, rewrite it to 0.\n"
" This option can be specified multiple times.\n"
" -v, --verbose Print debugging information to stderr.\n"
" -h, --help Print this help message and exit.\n"
" -V, --version Print the current version and exit.\n"
"\n"
"Full help is available online at https://github.com/Yelp/dumb-init\n",
VERSION,
Expand Down Expand Up @@ -175,14 +232,15 @@ void set_rewrite_to_sigstop_if_not_defined(int signum) {
char **parse_command(int argc, char *argv[]) {
int opt;
struct option long_options[] = {
{"help", no_argument, NULL, 'h'},
{"single-child", no_argument, NULL, 'c'},
{"rewrite", required_argument, NULL, 'r'},
{"verbose", no_argument, NULL, 'v'},
{"version", no_argument, NULL, 'V'},
{"help", no_argument, NULL, 'h'},
{"single-child", no_argument, NULL, 'c'},
{"rewrite", required_argument, NULL, 'r'},
{"verbose", no_argument, NULL, 'v'},
{"version", no_argument, NULL, 'V'},
{"survive-bereaving",no_argument, NULL, 'b'},
{NULL, 0, NULL, 0},
};
while ((opt = getopt_long(argc, argv, "+hvVcr:", long_options, NULL)) != -1) {
while ((opt = getopt_long(argc, argv, "+hvVcbr:", long_options, NULL)) != -1) {
switch (opt) {
case 'h':
print_help(argv);
Expand All @@ -199,6 +257,9 @@ char **parse_command(int argc, char *argv[]) {
case 'r':
parse_rewrite_signum(optarg);
break;
case 'b':
survive_bereaving = 1;
break;
default:
exit(1);
}
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Since survive_bereaving only works properly when dumb-init is running as PID 1, I think it'd be a good idea to add a check like:

if (survive_bereaving && getpid() != 1) {
    PRINTERR("--survive-bereaving is only valid when dumb-init is running as PID 1.\n");
    exit(1);
}

I think that would reduce confusion for anybody who tries to use the feature without being PID1.

Expand Down