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/* SPDX-License-Identifier: LGPL-2.1+ */
#include <errno.h>
#include "alloc-util.h"
#include "fileio.h"
#include "parse-util.h"
#include "process-util.h"
#include "procfs-util.h"
#include "stdio-util.h"
#include "string-util.h"
int procfs_tasks_get_limit(uint64_t *ret) {
_cleanup_free_ char *value = NULL;
uint64_t pid_max, threads_max;
int r;
assert(ret);
/* So there are two sysctl files that control the system limit of processes:
*
* 1. kernel.threads-max: this is probably the sysctl that makes more sense, as it directly puts a limit on
* concurrent tasks.
*
* 2. kernel.pid_max: this limits the numeric range PIDs can take, and thus indirectly also limits the number
* of concurrent threads. AFAICS it's primarily a compatibility concept: some crappy old code used a signed
* 16bit type for PIDs, hence the kernel provides a way to ensure the PIDs never go beyond INT16_MAX by
* default.
*
* By default #2 is set to much lower values than #1, hence the limit people come into contact with first, as
* it's the lowest boundary they need to bump when they want higher number of processes.
*
* Also note the weird definition of #2: PIDs assigned will be kept below this value, which means the number of
* tasks that can be created is one lower, as PID 0 is not a valid process ID. */
r = read_one_line_file("/proc/sys/kernel/pid_max", &value);
if (r < 0)
return r;
r = safe_atou64(value, &pid_max);
if (r < 0)
return r;
value = mfree(value);
r = read_one_line_file("/proc/sys/kernel/threads-max", &value);
if (r < 0)
return r;
r = safe_atou64(value, &threads_max);
if (r < 0)
return r;
/* Subtract one from pid_max, since PID 0 is not a valid PID */
*ret = MIN(pid_max-1, threads_max);
return 0;
}
int procfs_tasks_set_limit(uint64_t limit) {
char buffer[DECIMAL_STR_MAX(uint64_t)+1];
_cleanup_free_ char *value = NULL;
uint64_t pid_max;
int r;
if (limit == 0) /* This makes no sense, we are userspace and hence count as tasks too, and we want to live,
* hence the limit conceptually has to be above 0. Also, most likely if anyone asks for a zero
* limit he/she probably means "no limit", hence let's better refuse this to avoid
* confusion. */
return -EINVAL;
/* The Linux kernel doesn't allow this value to go below 20, hence don't allow this either, higher values than
* TASKS_MAX are not accepted by the pid_max sysctl. We'll treat anything this high as "unbounded" and hence
* set it to the maximum. */
limit = CLAMP(limit, 20U, TASKS_MAX);
r = read_one_line_file("/proc/sys/kernel/pid_max", &value);
if (r < 0)
return r;
r = safe_atou64(value, &pid_max);
if (r < 0)
return r;
/* As pid_max is about the numeric pid_t range we'll bump it if necessary, but only ever increase it, never
* decrease it, as threads-max is the much more relevant sysctl. */
if (limit > pid_max-1) {
sprintf(buffer, "%" PRIu64, limit+1); /* Add one, since PID 0 is not a valid PID */
r = write_string_file("/proc/sys/kernel/pid_max", buffer, WRITE_STRING_FILE_DISABLE_BUFFER);
if (r < 0)
return r;
}
sprintf(buffer, "%" PRIu64, limit);
r = write_string_file("/proc/sys/kernel/threads-max", buffer, WRITE_STRING_FILE_DISABLE_BUFFER);
if (r < 0) {
uint64_t threads_max;
/* Hmm, we couldn't write this? If so, maybe it was already set properly? In that case let's not
* generate an error */
value = mfree(value);
if (read_one_line_file("/proc/sys/kernel/threads-max", &value) < 0)
return r; /* return original error */
if (safe_atou64(value, &threads_max) < 0)
return r; /* return original error */
if (MIN(pid_max-1, threads_max) != limit)
return r; /* return original error */
/* Yay! Value set already matches what we were trying to set, hence consider this a success. */
}
return 0;
}
int procfs_tasks_get_current(uint64_t *ret) {
_cleanup_free_ char *value = NULL;
const char *p, *nr;
size_t n;
int r;
assert(ret);
r = read_one_line_file("/proc/loadavg", &value);
if (r < 0)
return r;
/* Look for the second part of the fourth field, which is separated by a slash from the first part. None of the
* earlier fields use a slash, hence let's use this to find the right spot. */
p = strchr(value, '/');
if (!p)
return -EINVAL;
p++;
n = strspn(p, DIGITS);
nr = strndupa(p, n);
return safe_atou64(nr, ret);
}
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