nginx学习—设置进程title(setproctitle)

刚好看到nginx设置进程title的源码，因此做一些总结。
linux进程实际是以argv[0]处的值来作为进程的title的，因此若需要修改进程的title只需要修改argv[0]处的值即可。
简单的方法就是直接将想要设置的title复制给argv[0]即可，如下示：

#include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> extern char** environ; int main(int argc, char* argv[]) {     char s_title[] = "xiejian title for simple way!";     size_t i_size = strlen(s_title);     memcpy(argv[0], s_title, i_size);     argv[0][i_size] = '\0';     while(1){         system("ps -ef|awk '$8 ~ /xiejian/ {print $0}'");         sleep(10);     }}

运行结果为：

但是这种方式是以破坏性的方式，进程的进程title的修改。由于程序的参数存储空间的后面紧跟的就是环境变量的存储位置，在不考虑参数的破坏性的情况下。
命令行参数argv和环境变量信息environ是在一块连续的内存中表示的，并且environ紧跟在argv后面。如下图：

由上图可知过长的title也会损坏环境变量environ的值。因此在nginx中，是将环境变量进行移位存储处理的。下面是nginx处理进程设置title的思路。

/* * To change the process title in Linux and Solaris we have to set argv[1] * to NULL and to copy the title to the same place where the argv[0] points to. * However, argv[0] may be too small to hold a new title.  Fortunately, Linux * and Solaris store argv[] and environ[] one after another.  So we should * ensure that is the continuous memory and then we allocate the new memory * for environ[] and copy it.  After this we could use the memory starting * from argv[0] for our process title. * * The Solaris's standard /bin/ps does not show the changed process title. * You have to use "/usr/ucb/ps -w" instead.  Besides, the UCB ps does not * show a new title if its length less than the origin command line length. * To avoid it we append to a new title the origin command line in the * parenthesis. */

然后由于nginx中考虑多进程的情况，因此他会在初始化时就完成environ的迁移。下面是初始化函数

//指向环境变量，默认的extern char **environ;//指向之前的用于存放参数及环境变量的空间的最后位置。static char *ngx_os_argv_last;ngx_int_tngx_init_setproctitle(ngx_log_t *log){    u_char      *p;    size_t       size;    ngx_uint_t   i;    size = 0;//计算环境变量所用的总的空间的大小，然后以申请足够的空间用于存放环境变量    for (i = 0; environ[i]; i++) {        size += ngx_strlen(environ[i]) + 1;    }    //为环境就是分配空间    p = ngx_alloc(size, log);    if (p == NULL) {        return NGX_ERROR;    }    //下面开始计算前面用于存放环境变量的最后位置ngx_os_argv_last = ngx_os_argv[0];//首先计算参数的最后位置    for (i = 0; ngx_os_argv[i]; i++) {        if (ngx_os_argv_last == ngx_os_argv[i]) {            ngx_os_argv_last = ngx_os_argv[i] + ngx_strlen(ngx_os_argv[i]) + 1;        }    }    //再计算环境变量占用的最后位置，并完成环境变量的拷贝    for (i = 0; environ[i]; i++) {        if (ngx_os_argv_last == environ[i]) {            size = ngx_strlen(environ[i]) + 1;            ngx_os_argv_last = environ[i] + size;            ngx_cpystrn(p, (u_char *) environ[i], size);            environ[i] = (char *) p;            p += size;        }    }    ngx_os_argv_last--;    return NGX_OK;}

然后是具体的设置title的函数:

voidngx_setproctitle(char *title){    u_char     *p;#if (NGX_SOLARIS)    ngx_int_t   i;    size_t      size;#endif    ngx_os_argv[1] = NULL;    p = ngx_cpystrn((u_char *) ngx_os_argv[0], (u_char *) "nginx: ",                    ngx_os_argv_last - ngx_os_argv[0]);    p = ngx_cpystrn(p, (u_char *) title, ngx_os_argv_last - (char *) p);#if (NGX_SOLARIS)    size = 0;    for (i = 0; i < ngx_argc; i++) {        size += ngx_strlen(ngx_argv[i]) + 1;    }    if (size > (size_t) ((char *) p - ngx_os_argv[0])) {        /*         * ngx_setproctitle() is too rare operation so we use         * the non-optimized copies         */        p = ngx_cpystrn(p, (u_char *) " (", ngx_os_argv_last - (char *) p);        for (i = 0; i < ngx_argc; i++) {            p = ngx_cpystrn(p, (u_char *) ngx_argv[i],                            ngx_os_argv_last - (char *) p);            p = ngx_cpystrn(p, (u_char *) " ", ngx_os_argv_last - (char *) p);        }        if (*(p - 1) == ' ') {            *(p - 1) = ')';        }    }#endif    if (ngx_os_argv_last - (char *) p) {        ngx_memset(p, NGX_SETPROCTITLE_PAD, ngx_os_argv_last - (char *) p);    }    ngx_log_debug1(NGX_LOG_DEBUG_CORE, ngx_cycle->log, 0,                   "setproctitle: \"%s\"", ngx_os_argv[0]);}

最后就是根据nginx的思想的一个简单修改title的示例：

#include <unistd.h>  #include <stdio.h>#include <stdlib.h>#include <string.h>#define  NGX_OK          0#define  NGX_ERROR      -1#define NGX_SETPROCTITLE_PAD       '\0'typedef int                 ngx_int_t;typedef unsigned int        ngx_uint_t;extern char **environ;static char *ngx_os_argv_last;int              ngx_argc;char           **ngx_os_argv;u_char *ngx_cpystrn(u_char *dst, u_char *src, size_t n){    if (n == 0) {        return dst;    }    while (--n) {        *dst = *src;        if (*dst == '\0') {            return dst;        }        dst++;        src++;    }    *dst = '\0';    return dst;}ngx_int_tngx_init_setproctitle(){    u_char      *p;    size_t       size;    ngx_uint_t   i;    size = 0;    for (i = 0; environ[i]; i++) {        size += strlen(environ[i]) + 1;    }    p = malloc(size);    if (p == NULL) {        return NGX_ERROR;    }    ngx_os_argv_last = ngx_os_argv[0];    for (i = 0; ngx_os_argv[i]; i++) {        if (ngx_os_argv_last == ngx_os_argv[i]) {            ngx_os_argv_last = ngx_os_argv[i] + strlen(ngx_os_argv[i]) + 1;        }    }    for (i = 0; environ[i]; i++) {        if (ngx_os_argv_last == environ[i]) {            size = strlen(environ[i]) + 1;            ngx_os_argv_last = environ[i] + size;            ngx_cpystrn(p, (u_char *) environ[i], size);            environ[i] = (char *) p;            p += size;        }    }    ngx_os_argv_last--;    return NGX_OK;}voidngx_setproctitle(char *title){    u_char     *p;    ngx_os_argv[1] = NULL;    p = ngx_cpystrn((u_char *) ngx_os_argv[0], (u_char *) "nginx: ",                    ngx_os_argv_last - ngx_os_argv[0]);    p = ngx_cpystrn(p, (u_char *) title, ngx_os_argv_last - (char *) p);    if (ngx_os_argv_last - (char *) p) {        memset(p, NGX_SETPROCTITLE_PAD, ngx_os_argv_last - (char *) p);    }}static ngx_int_tngx_save_argv(int argc, char *const *argv){    ngx_os_argv = (char **) argv;    ngx_argc = argc;    return NGX_OK;}int main(int argc, char *const *argv){      ngx_save_argv(argc,argv);    ngx_init_setproctitle();    ngx_setproctitle("xiejian test");    while(1){        system("ps -ef|awk '$8 ~ /nginx/ {print $0}'");        sleep(10);    }  return (0);  }

运行结果为：