source: vendor/current/ctdb/common/pidfile.c

/*
   Create and remove pidfile

   Copyright (C) Amitay Isaacs  2016

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, see <http://www.gnu.org/licenses/>.
*/

#include "replace.h"
#include "system/filesys.h"

#include <talloc.h>

#include "common/pidfile.h"

struct pidfile_context {
        const char *pidfile;
        int fd;
        pid_t pid;
};

static int pidfile_context_destructor(struct pidfile_context *pid_ctx);

int pidfile_create(TALLOC_CTX *mem_ctx, const char *pidfile,
                   struct pidfile_context **result)
{
        struct pidfile_context *pid_ctx;
        struct flock lck;
        char tmp[64];
        int fd, ret = 0;
        int len;
        ssize_t nwritten;

        pid_ctx = talloc_zero(mem_ctx, struct pidfile_context);
        if (pid_ctx == NULL) {
                return ENOMEM;
        }

        pid_ctx->pidfile = talloc_strdup(pid_ctx, pidfile);
        if (pid_ctx->pidfile == NULL) {
                ret = ENOMEM;
                goto fail;
        }

        pid_ctx->pid = getpid();

        fd = open(pidfile, O_CREAT|O_WRONLY|O_NONBLOCK, 0644);
        if (fd == -1) {
                ret = errno;
                goto fail;
        }

        pid_ctx->fd = fd;

        lck = (struct flock) {
                .l_type = F_WRLCK,
                .l_whence = SEEK_SET,
        };

        do {
                ret = fcntl(fd, F_SETLK, &lck);
        } while ((ret == -1) && (errno == EINTR));

        if (ret != 0) {
                ret = errno;
                goto fail;
        }

        do {
                ret = ftruncate(fd, 0);
        } while ((ret == -1) && (errno == EINTR));

        if (ret == -1) {
                ret = EIO;
                goto fail_unlink;
        }

        len = snprintf(tmp, sizeof(tmp), "%u\n", pid_ctx->pid);
        if (len < 0) {
                ret = EIO;
                goto fail_unlink;
        }

        do {
                nwritten = write(fd, tmp, len);
        } while ((nwritten == -1) && (errno == EINTR));

        if ((nwritten == -1) || (nwritten != len)) {
                ret = EIO;
                goto fail_unlink;
        }

        talloc_set_destructor(pid_ctx, pidfile_context_destructor);

        *result = pid_ctx;
        return 0;

fail_unlink:
        unlink(pidfile);
        close(fd);

fail:
        talloc_free(pid_ctx);
        return ret;
}

static int pidfile_context_destructor(struct pidfile_context *pid_ctx)
{
        struct flock lck;
        int ret;

        if (getpid() != pid_ctx->pid) {
                return 0;
        }

        lck = (struct flock) {
                .l_type = F_UNLCK,
                .l_whence = SEEK_SET,
        };

        (void) unlink(pid_ctx->pidfile);

        do {
                ret = fcntl(pid_ctx->fd, F_SETLK, &lck);
        } while ((ret == -1) && (errno == EINTR));

        do {
                ret = close(pid_ctx->fd);
        } while ((ret == -1) && (errno == EINTR));

        return 0;
}