procpsのpgrepのコードリーディング

はじめに

procps-ngのpgrepのコードリーディング に続いて CentOS 6 の pgrep についてもコードリーディングしてみました。 pgrep を含むパッケージは procps でバージョンは3.2.8でした。

[root@centos6 ~]# rpm -qf `which pgrep`
procps-3.2.8-36.el6.x86_64

procps のプロジェクトページは procps - Home Page で、 SourceForge.net Repository - [procps] Index of / でソースコードが見られます。

一方で以下のコマンドで srpm をダウンロードしてそこから pgrep.c を取り出しました。

[root@centos6 ~]# curl -sO http://vault.centos.org/6.8/os/Source/SPackages/procps-3.2.8-36.el6.src.rpm
[root@centos6 ~]# mkdir procps-srpm
[root@centos6 ~]# rpm2cpio procps-3.2.8-36.el6.src.rpm | (cd procps-srpm && cpio -idm --quiet)
[root@centos6 ~]# tar xf procps-srpm/procps-3.2.8.tar.gz -C procps-srpm

SourceForge.net Repository - [procps] Log of /procps/pgrep.c の各リビジョンと上記で取り出した pgrep.c を比較したところ SourceForge.net Repository - [procps] Contents of /procps/pgrep.c revision 1.29 と一致していました。

pgrep.cのコードリーディング

main 関数の実装。 pgrep.c#L709-#L732

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int main (int argc, char *argv[])
{
    union el *procs;
    int num;

    parse_opts (argc, argv);

    procs = select_procs (&num);
    if (i_am_pkill) {
            int i;
            for (i = 0; i < num; i++) {
                    if (kill (procs[i].num, opt_signal) != -1) continue;
                    if (errno==ESRCH) continue; // gone now, which is OK
                    fprintf (stderr, "pkill: %ld - %s\n",
                             procs[i].num, strerror (errno));
            }
    } else {
            if (opt_long)
                    output_strlist(procs,num);
            else
                    output_numlist(procs,num);
    }
    return !num; // exit(EXIT_SUCCESS) if match, otherwise exit(EXIT_FAILURE)
}

parse_opts 関数の実装。 pgrep.c#L539-#L706

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static void parse_opts (int argc, char **argv)
{
    char opts[32] = "";
    int opt;
    int criteria_count = 0;

    if (strstr (argv[0], "pkill")) {
            i_am_pkill = 1;
            progname = "pkill";
            /* Look for a signal name or number as first argument */
            if (argc > 1 && argv[1][0] == '-') {
                    int sig;
                    sig = signal_name_to_number (argv[1] + 1);
                    if (sig == -1 && isdigit (argv[1][1]))
                            sig = atoi (argv[1] + 1);
                    if (sig != -1) {
                            int i;
                            for (i = 2; i < argc; i++)
                                    argv[i-1] = argv[i];
                            --argc;
                            opt_signal = sig;
                    }
            }
    } else {
            /* These options are for pgrep only */
            strcat (opts, "ld:");
    }

    strcat (opts, "LF:fnovxP:g:s:u:U:G:t:?V");

    while ((opt = getopt (argc, argv, opts)) != -1) {
            switch (opt) {
//          case 'D':   // FreeBSD: print info about non-matches for debugging
//                  break;
            case 'F':   // FreeBSD: the arg is a file containing a PID to match
                    opt_pidfile = strdup (optarg);
                    ++criteria_count;
                    break;
            case 'G':   // Solaris: match rgid/rgroup
                    opt_rgid = split_list (optarg, conv_gid);
                    if (opt_rgid == NULL)
                            usage (opt);
                    ++criteria_count;
                    break;
//          case 'I':   // FreeBSD: require confirmation before killing
//                  break;
//          case 'J':   // Solaris: match by project ID (name or number)
//                  break;
            case 'L':   // FreeBSD: fail if pidfile (see -F) not locked
                    opt_lock++;
                    break;
//          case 'M':   // FreeBSD: specify core (OS crash dump) file
//                  break;
//          case 'N':   // FreeBSD: specify alternate namelist file (for us, System.map -- but we don't need it)
//                  break;
            case 'P':   // Solaris: match by PPID
                    opt_ppid = split_list (optarg, conv_num);
                    if (opt_ppid == NULL)
                            usage (opt);
                    ++criteria_count;
                    break;
//          case 'S':   // FreeBSD: don't ignore the built-in kernel tasks
//                  break;
//          case 'T':   // Solaris: match by "task ID" (probably not a Linux task)
//                  break;
            case 'U':   // Solaris: match by ruid/rgroup
                    opt_ruid = split_list (optarg, conv_uid);
                    if (opt_ruid == NULL)
                            usage (opt);
                    ++criteria_count;
                    break;
            case 'V':
                    fprintf(stdout, "%s (%s)\n", progname, procps_version);
                    exit(EXIT_SUCCESS);
//          case 'c':   // Solaris: match by contract ID
//                  break;
            case 'd':   // Solaris: change the delimiter
                    opt_delim = strdup (optarg);
                    break;
            case 'f':   // Solaris: match full process name (as in "ps -f")
                    opt_full = 1;
                    break;
            case 'g':   // Solaris: match pgrp
                    opt_pgrp = split_list (optarg, conv_pgrp);
                    if (opt_pgrp == NULL)
                            usage (opt);
                    ++criteria_count;
                    break;
//          case 'i':   // FreeBSD: ignore case. OpenBSD: withdrawn. See -I. This sucks.
//                  if (opt_case)
//                          usage (opt);
//                  opt_case = REG_ICASE;
//                  break;
//          case 'j':   // FreeBSD: restricted to the given jail ID
//                  break;
            case 'l':   // Solaris: long output format (pgrep only) Should require -f for beyond argv[0] maybe?
                    opt_long = 1;
                    break;
            case 'n':   // Solaris: match only the newest
                    if (opt_oldest|opt_negate|opt_newest)
                            usage (opt);
                    opt_newest = 1;
                    ++criteria_count;
                    break;
            case 'o':   // Solaris: match only the oldest
                    if (opt_oldest|opt_negate|opt_newest)
                            usage (opt);
                    opt_oldest = 1;
                    ++criteria_count;
                    break;
            case 's':   // Solaris: match by session ID -- zero means self
                    opt_sid = split_list (optarg, conv_sid);
                    if (opt_sid == NULL)
                            usage (opt);
                    ++criteria_count;
                    break;
            case 't':   // Solaris: match by tty
                    opt_term = split_list (optarg, conv_str);
                    if (opt_term == NULL)
                            usage (opt);
                    ++criteria_count;
                    break;
            case 'u':   // Solaris: match by euid/egroup
                    opt_euid = split_list (optarg, conv_uid);
                    if (opt_euid == NULL)
                            usage (opt);
                    ++criteria_count;
                    break;
            case 'v':   // Solaris: as in grep, invert the matching (uh... applied after selection I think)
                    if (opt_oldest|opt_negate|opt_newest)
                            usage (opt);
                    opt_negate = 1;
                    break;
            // OpenBSD -x, being broken, does a plain string
            case 'x':   // Solaris: use ^(regexp)$ in place of regexp (FreeBSD too)
                    opt_exact = 1;
                    break;
//          case 'z':   // Solaris: match by zone ID
//                  break;
            case '?':
                    usage (opt);
                    break;
            }
    }

    if(opt_lock && !opt_pidfile){
            fprintf(stderr, "%s: -L without -F makes no sense\n",progname);
            usage(0);
    }

    if(opt_pidfile){
            opt_pid = read_pidfile();
            if(!opt_pid){
                    fprintf(stderr, "%s: pidfile not valid\n",progname);
                    usage(0);
            }
    }

        if (argc - optind == 1)
            opt_pattern = argv[optind];
    else if (argc - optind > 1)
            usage (0);
    else if (criteria_count == 0) {
            fprintf (stderr, "%s: No matching criteria specified\n",
                     progname);
            usage (0);
    }
}

-f オプションで opt_full = 1; が実行され -l オプションで opt_long = 1; が実行されます。

output_strlist 関数の実装。 pgrep.c#L343-#L353

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static void output_strlist (const union el *restrict list, int num)
{
// FIXME: escape codes
    int i;
    const char *delim = opt_delim;
    for (i = 0; i < num; i++) {
            if(i+1==num)
                    delim = "\n";
            printf ("%s%s", list[i].str, delim);
    }
}

select_procs 関数の実装。 pgrep.c#L416-#L536

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static union el * select_procs (int *num)
{
    PROCTAB *ptp;
    proc_t task;
    unsigned long long saved_start_time;      // for new/old support
    pid_t saved_pid = 0;                      // for new/old support
    int matches = 0;
    int size = 0;
    regex_t *preg;
    pid_t myself = getpid();
    union el *list = NULL;
    char cmd[4096];

    ptp = do_openproc();
    preg = do_regcomp();

    if (opt_newest) saved_start_time =  0ULL;
    if (opt_oldest) saved_start_time = ~0ULL;
    if (opt_newest) saved_pid = 0;
    if (opt_oldest) saved_pid = INT_MAX;

    memset(&task, 0, sizeof (task));
    while(readproc(ptp, &task)) {
            int match = 1;

            if (task.XXXID == myself)
                    continue;
            else if (opt_newest && task.start_time < saved_start_time)
                    match = 0;
            else if (opt_oldest && task.start_time > saved_start_time)
                    match = 0;
            else if (opt_ppid && ! match_numlist (task.ppid, opt_ppid))
                    match = 0;
            else if (opt_pid && ! match_numlist (task.tgid, opt_pid))
                    match = 0;
            else if (opt_pgrp && ! match_numlist (task.pgrp, opt_pgrp))
                    match = 0;
            else if (opt_euid && ! match_numlist (task.euid, opt_euid))
                    match = 0;
            else if (opt_ruid && ! match_numlist (task.ruid, opt_ruid))
                    match = 0;
            else if (opt_rgid && ! match_numlist (task.rgid, opt_rgid))
                    match = 0;
            else if (opt_sid && ! match_numlist (task.session, opt_sid))
                    match = 0;
            else if (opt_term) {
                    if (task.tty == 0) {
                            match = 0;
                    } else {
                            char tty[256];
                            dev_to_tty (tty, sizeof(tty) - 1,
                                        task.tty, task.XXXID, ABBREV_DEV);
                            match = match_strlist (tty, opt_term);
                    }
            }
            if (opt_long || (match && opt_pattern)) {
                    if (opt_full && task.cmdline) {
                            int i = 0;
                            int bytes = sizeof (cmd) - 1;

                            /* make sure it is always NUL-terminated */
                            cmd[bytes] = 0;
                            /* make room for SPC in loop below */
                            --bytes;

                            strncpy (cmd, task.cmdline[i], bytes);
                            bytes -= strlen (task.cmdline[i++]);
                            while (task.cmdline[i] && bytes > 0) {
                                    strncat (cmd, " ", bytes);
                                    strncat (cmd, task.cmdline[i], bytes);
                                    bytes -= strlen (task.cmdline[i++]) + 1;
                            }
                    } else {
                            strcpy (cmd, task.cmd);
                    }
            }

            if (match && opt_pattern) {
                    if (regexec (preg, cmd, 0, NULL, 0) != 0)
                            match = 0;
            }

            if (match ^ opt_negate) {       /* Exclusive OR is neat */
                    if (opt_newest) {
                            if (saved_start_time == task.start_time &&
                                saved_pid > task.XXXID)
                                    continue;
                            saved_start_time = task.start_time;
                            saved_pid = task.XXXID;
                            matches = 0;
                    }
                    if (opt_oldest) {
                            if (saved_start_time == task.start_time &&
                                saved_pid < task.XXXID)
                                    continue;
                            saved_start_time = task.start_time;
                            saved_pid = task.XXXID;
                            matches = 0;
                    }
                    if (matches == size) {
                            size = size * 5 / 4 + 4;
                            list = realloc(list, size * sizeof *list);
                            if (list == NULL)
                                    exit (EXIT_FATAL);
                    }
                    if (opt_long) {
                            char buff[5096];  // FIXME
                            sprintf (buff, "%d %s", task.XXXID, cmd);
                            list[matches++].str = strdup (buff);
                    } else {
                            list[matches++].num = task.XXXID;
                    }
            }

            memset (&task, 0, sizeof (task));
    }
    closeproc (ptp);

    *num = matches;
    return list;
}

stat2proc 関数の実装。 proc/readproc.c#L336-#L356

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// Reads /proc/*/stat files, being careful not to trip over processes with
// names like ":-) 1 2 3 4 5 6".
static void stat2proc(const char* S, proc_t *restrict P) {
    unsigned num;
    char* tmp;

ENTER(0x160);

    /* fill in default values for older kernels */
    P->processor = 0;
    P->rtprio = -1;
    P->sched = -1;
    P->nlwp = 0;

    S = strchr(S, '(') + 1;
    tmp = strrchr(S, ')');
    num = tmp - S;
    if(unlikely(num >= sizeof P->cmd)) num = sizeof P->cmd - 1;
    memcpy(P->cmd, S, num);
    P->cmd[num] = '\0';
    S = tmp + 2;                 // skip ") "

ということで /proc/${PID}/stat の出力の () の間が task.cmd に設定され、 -f を指定しない場合はこれがマッチの対象になります。 -f を設定した場合はコマンドライン全体がマッチの対象になります。