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Message-ID: <957483b9-a4f3-fcea-b6bc-02ad56b2e699@huawei.com>
Date:   Mon, 21 Nov 2022 09:39:31 +0800
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Subject: Re: [PATCH v4] nfs-blkmapd: PID file read by systemd failed
To:     Steve Dickson <steved@redhat.com>
CC:     <linux-nfs@vger.kernel.org>, linfeilong <linfeilong@huawei.com>,
        <liuzhiqiang26@huawei.com>
References: <3e9dfa44-7448-bf0a-8359-7c8229c45246@huawei.com>
 <91bc13b0-8ed7-1f67-f39a-1ce34e16e59b@redhat.com>
From:   zhanchengbin <zhanchengbin1@huawei.com>
In-Reply-To: <91bc13b0-8ed7-1f67-f39a-1ce34e16e59b@redhat.com>
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Thanks.

On 2022/11/20 3:49, Steve Dickson wrote:
> 
> 
> On 11/8/22 10:48 PM, zhanchengbin wrote:
>> When started nfs-blkmap.service, the PID file can't be opened, The
>> cause is that the child process does not create the PID file before
>> the systemd reads the PID file.
>> Adding "ExecStartPost=/bin/sleep 0.1" to
>> /usr/lib/systemd/system/nfs-blkmap.service will probably solve this
>> problem, However, there is no guarantee that the above solutions are
>> effective under high cpu pressure.So replace the daemon function with
>> the fork function, and put the behavior of creating the PID file in
>> the parent process to solve the above problems.
>>
>> Signed-off-by: zhanchengbin <zhanchengbin1@huawei.com>
>> Signed-off-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
> Committed...
> 
> steved.
>> ---
>> V3->V4:
>>   The previous version cannot be applied.
>>
>>   utils/blkmapd/device-discovery.c | 48 +++++++++++++++++++++-----------
>>   1 file changed, 32 insertions(+), 16 deletions(-)
>>
>> diff --git a/utils/blkmapd/device-discovery.c 
>> b/utils/blkmapd/device-discovery.c
>> index bd890598..a565fdbd 100644
>> --- a/utils/blkmapd/device-discovery.c
>> +++ b/utils/blkmapd/device-discovery.c
>> @@ -498,28 +498,44 @@ int main(int argc, char **argv)
>>       if (fg) {
>>           openlog("blkmapd", LOG_PERROR, 0);
>>       } else {
>> -        if (daemon(0, 0) != 0) {
>> -            fprintf(stderr, "Daemonize failed\n");
>> +        pid_t pid = fork();
>> +        if (pid < 0) {
>> +            BL_LOG_ERR("fork error\n");
>>               exit(1);
>> +        } else if (pid != 0) {
>> +            pidfd = open(PID_FILE, O_WRONLY | O_CREAT, 0644);
>> +            if (pidfd < 0) {
>> +                BL_LOG_ERR("Create pid file %s failed\n", PID_FILE);
>> +                exit(1);
>> +            }
>> +
>> +            if (lockf(pidfd, F_TLOCK, 0) < 0) {
>> +                BL_LOG_ERR("Already running; Exiting!");
>> +                close(pidfd);
>> +                exit(1);
>> +            }
>> +            if (ftruncate(pidfd, 0) < 0)
>> +                BL_LOG_ERR("ftruncate on %s failed: m\n", PID_FILE);
>> +            sprintf(pidbuf, "%d\n", pid);
>> +            if (write(pidfd, pidbuf, strlen(pidbuf)) != 
>> (ssize_t)strlen(pidbuf))
>> +                BL_LOG_ERR("write on %s failed: m\n", PID_FILE);
>> +            exit(0);
>>           }
>>
>> -        openlog("blkmapd", LOG_PID, 0);
>> -        pidfd = open(PID_FILE, O_WRONLY | O_CREAT, 0644);
>> -        if (pidfd < 0) {
>> -            BL_LOG_ERR("Create pid file %s failed\n", PID_FILE);
>> -            exit(1);
>> +        (void)setsid();
>> +        if (chdir("/")) {
>> +            BL_LOG_ERR("chdir error\n");
>>           }
>> +        int fd = open("/dev/null", O_RDWR, 0);
>> +        if (fd >= 0) {
>> +            (void)dup2(fd, STDIN_FILENO);
>> +            (void)dup2(fd, STDOUT_FILENO);
>> +            (void)dup2(fd, STDERR_FILENO);
>>
>> -        if (lockf(pidfd, F_TLOCK, 0) < 0) {
>> -            BL_LOG_ERR("Already running; Exiting!");
>> -            close(pidfd);
>> -            exit(1);
>> +            (void)close(fd);
>>           }
>> -        if (ftruncate(pidfd, 0) < 0)
>> -            BL_LOG_WARNING("ftruncate on %s failed: m\n", PID_FILE);
>> -        sprintf(pidbuf, "%d\n", getpid());
>> -        if (write(pidfd, pidbuf, strlen(pidbuf)) != 
>> (ssize_t)strlen(pidbuf))
>> -            BL_LOG_WARNING("write on %s failed: m\n", PID_FILE);
>> +
>> +        openlog("blkmapd", LOG_PID, 0);
>>       }
>>
>>       signal(SIGINT, sig_die);
> 
> .