/* vi: set sw=4 ts=4: */
/*
 * chrt - manipulate real-time attributes of a process
 * Copyright (c) 2006-2007 Bernhard Reutner-Fischer
 *
 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
 */
//config:config CHRT
//config:       bool "chrt (4.7 kb)"
//config:       default y
//config:       help
//config:       Manipulate real-time attributes of a process.
//config:       This requires sched_{g,s}etparam support in your libc.

//applet:IF_CHRT(APPLET_NOEXEC(chrt, chrt, BB_DIR_USR_BIN, BB_SUID_DROP, chrt))

//kbuild:lib-$(CONFIG_CHRT) += chrt.o

//usage:#define chrt_trivial_usage
//usage:       "-m | -p [PRIO] PID | [-rfobi] PRIO PROG ARGS"
//usage:#define chrt_full_usage "\n\n"
//usage:       "Change scheduling priority and class for a process\n"
//usage:     "\n        -m      Show min/max priorities"
//usage:     "\n        -p      Operate on PID"
//usage:     "\n        -r      Set SCHED_RR class"
//usage:     "\n        -f      Set SCHED_FIFO class"
//usage:     "\n        -o      Set SCHED_OTHER class"
//usage:     "\n        -b      Set SCHED_BATCH class"
//usage:     "\n        -i      Set SCHED_IDLE class"
//usage:
//usage:#define chrt_example_usage
//usage:       "$ chrt -r 4 sleep 900; x=$!\n"
//usage:       "$ chrt -f -p 3 $x\n"
//usage:       "You need CAP_SYS_NICE privileges to set scheduling attributes of a process"

#include <sched.h>
#include "libbb.h"
#ifndef SCHED_IDLE
# define SCHED_IDLE 5
#endif

//musl has no __MUSL__ or similar define to check for,
//but its <sys/types.h> has these lines:
// #define __NEED_fsblkcnt_t
// #define __NEED_fsfilcnt_t
#if defined(__linux__) && defined(__NEED_fsblkcnt_t) && defined(__NEED_fsfilcnt_t)
# define LIBC_IS_MUSL 1
# include <sys/syscall.h>
#else
# define LIBC_IS_MUSL 0
#endif

static const char *policy_name(int pol)
{
        if (pol > 6)
                return utoa(pol);
        return nth_string(
                "OTHER"   "\0" /* 0:SCHED_OTHER */
                "FIFO"    "\0" /* 1:SCHED_FIFO */
                "RR"      "\0" /* 2:SCHED_RR */
                "BATCH"   "\0" /* 3:SCHED_BATCH */
                "ISO"     "\0" /* 4:SCHED_ISO */
                "IDLE"    "\0" /* 5:SCHED_IDLE */
                "DEADLINE",    /* 6:SCHED_DEADLINE */
                pol
        );
}

static void show_min_max(int pol)
{
        const char *fmt = "SCHED_%s min/max priority\t: %u/%u\n";
        int max, min;

        max = sched_get_priority_max(pol);
        min = sched_get_priority_min(pol);
        if ((max|min) < 0)
                fmt = "SCHED_%s not supported\n";
        printf(fmt, policy_name(pol), min, max);
}

#define OPT_m (1<<0)
#define OPT_p (1<<1)
#define OPT_r (1<<2)
#define OPT_f (1<<3)
#define OPT_o (1<<4)
#define OPT_b (1<<5)
#define OPT_i (1<<6)

int chrt_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int chrt_main(int argc UNUSED_PARAM, char **argv)
{
        pid_t pid = 0;
        unsigned opt;
        struct sched_param sp;
        char *pid_str;
        char *priority = NULL;
        const char *current_new;
        int policy = SCHED_RR;
        int ret;

        opt = getopt32(argv, "^"
                        "+" "mprfobi"
                        "\0"
                        /* only one policy accepted: */
                        "r--fobi:f--robi:o--rfbi:b--rfoi:i--rfob"
        );
        if (opt & OPT_m) { /* print min/max and exit */
                show_min_max(SCHED_OTHER);
                show_min_max(SCHED_FIFO);
                show_min_max(SCHED_RR);
                show_min_max(SCHED_BATCH);
                show_min_max(SCHED_IDLE);
                fflush_stdout_and_exit(EXIT_SUCCESS);
        }
        //if (opt & OPT_r)
        //      policy = SCHED_RR; - default, already set
        if (opt & OPT_f)
                policy = SCHED_FIFO;
        if (opt & OPT_o)
                policy = SCHED_OTHER;
        if (opt & OPT_b)
                policy = SCHED_BATCH;
        if (opt & OPT_i)
                policy = SCHED_IDLE;

        argv += optind;
        if (!argv[0])
                bb_show_usage();
        if (opt & OPT_p) {
                pid_str = *argv++;
                if (*argv) { /* "-p PRIO PID [...]" */
                        priority = pid_str;
                        pid_str = *argv;
                }
                /* else "-p PID", and *argv == NULL */
                pid = xatoul_range(pid_str, 1, ((unsigned)(pid_t)ULONG_MAX) >> 1);
        } else {
                priority = *argv++;
                if (!*argv)
                        bb_show_usage();
        }

        current_new = "current\0new";
        if (opt & OPT_p) {
                int pol;
 print_rt_info:
#if LIBC_IS_MUSL
                /* musl libc returns ENOSYS for its sched_getscheduler library
                 * function, because the sched_getscheduler Linux kernel system call
                 * does not conform to Posix; so we use the system call directly
                 */
                pol = syscall(SYS_sched_getscheduler, pid);
#else
                pol = sched_getscheduler(pid);
#endif
                if (pol < 0)
                        bb_perror_msg_and_die("can't %cet pid %u's policy", 'g', (int)pid);
#ifdef SCHED_RESET_ON_FORK
                /* "Since Linux 2.6.32, the SCHED_RESET_ON_FORK flag
                 * can be ORed in policy when calling sched_setscheduler().
                 * As a result of including this flag, children created by
                 * fork(2) do not inherit privileged scheduling policies"
                 *
                 * This bit is also returned by sched_getscheduler()!
                 * (TODO: do we want to show it?)
                 */
                pol &= ~SCHED_RESET_ON_FORK;
#endif
                printf("pid %u's %s scheduling policy: SCHED_%s\n",
                        pid, current_new, policy_name(pol)
                );
#if LIBC_IS_MUSL
                ret = syscall(SYS_sched_getparam, pid, &sp);
#else
                ret = sched_getparam(pid, &sp);
#endif
                if (ret)
                        bb_perror_msg_and_die("can't get pid %u's attributes", (int)pid);
                printf("pid %u's %s scheduling priority: %d\n",
                        (int)pid, current_new, sp.sched_priority
                );
                if (!*argv) {
                        /* Either it was just "-p PID",
                         * or it was "-p PRIO PID" and we came here
                         * for the second time (see goto below) */
                        return EXIT_SUCCESS;
                }
                *argv = NULL;
                current_new += 8;
        }

        sp.sched_priority = xstrtou_range(priority, 0,
                sched_get_priority_min(policy), sched_get_priority_max(policy)
        );

#if LIBC_IS_MUSL
        ret = syscall(SYS_sched_setscheduler, pid, policy, &sp);
#else
        ret = sched_setscheduler(pid, policy, &sp);
#endif
        if (ret)
                bb_perror_msg_and_die("can't %cet pid %u's policy", 's', (int)pid);

        if (!argv[0]) /* "-p PRIO PID [...]" */
                goto print_rt_info;

        BB_EXECVP_or_die(argv);
}