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1.1 介绍
每一个c程序都有个main函数,作为程序启动入口函数。main函数的原型是int main(int argc , char *argv[]);其中argc表示命令行参数的个数;argv是一个指针数组,保存所有命令行字符串。Linux进程名称是通过命令行参数argv[0]来表示的。
Linux 还有环境变量参数信息,表示进程执行需要的所有环境变量信息。通过全局变量
Char **environ;可以访问环境变量。
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:
1.2 验证argv和environ执行连续内存的测试程序
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1 #include
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2 #include
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3
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4 extern char **environ;
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5 int main(int argc , char *argv[])
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6 {
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7 int i;
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8
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9 printf("argc:%d\n" , argc);
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10
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11 for (i = 0; i < argc; ++i){
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12 printf("%x\n" , argv[i]);
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13 printf("argv[%d]:%s\n" , i , argv[i]);
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14 }
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15
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16 printf("evriron=%x\n" , environ[0]);
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17
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18 return 0;
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19 }
root@VM-Ubuntu203001:~/test#gcc -o test main.c
root@VM-Ubuntu203001:~/test#./test -p /usr/local/nginx -n 32
argc:5
bfa0c8f2
argv[0]:./test
bfa0c8f9
argv[1]:-p
bfa0c8fc
argv[2]:/usr/local/nginx
bfa0c90d
argv[3]:-n
bfa0c910
argv[4]:32
evriron=bfa0c913
1.3 修改进程名称
按理说,修改进程名称,只需要修改argv[0]指向的内存的值为所需要的值即可。但是当我们要修改的值超过argv[0]所指向的内存空间大小时,再这样直接修改,就会覆盖掉一部分argv[1]的值,因为从上面的图中,很容易就可以看出。
这时候,该怎么做呢?
1、必须重新分配一块连续的内存空间,把argv和environ的参数都复制到新的空间。
2、修改argv[0]为所需要修改的值。
1.4 Nginx的做法
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* To change the process title in Linux andSolaris we have to set argv[1]
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* to NULL and to copy the title to the sameplace where the argv[0] points to.
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* However, argv[0] may be too small to hold anew title. Fortunately, Linux
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* and Solaris store argv[] and environ[] oneafter another. So we should
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* ensure that is the continuous memory andthen we allocate the new memory
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* for environ[] and copy it. After this we could use the memory starting
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* from argv[0] for our process title.
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*
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* The Solaris's standard /bin/ps does not showthe changed process title.
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* You have to use "/usr/ucb/ps -w"instead. Besides, the UCB ps does not
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* show a new title if its length less than theorigin command line length.
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* To avoid it we append to a new title theorigin command line in the
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* parenthesis.
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*/
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extern char **environ;
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static char *ngx_os_argv_last;
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ngx_int_t
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ngx_init_setproctitle(ngx_log_t *log)
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{
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u_char *p;
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size_t size;
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ngx_uint_t i;
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size = 0;
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for (i = 0; environ[i]; i++) {
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size+= ngx_strlen(environ[i]) + 1;
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}
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p = ngx_alloc(size, log);
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if (p == NULL) {
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return NGX_ERROR;
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}
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/*
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这是为了找出argv和environ指向连续内存空间结尾的位置,为了能处理argv[i]被修改后,指向非进程启动时所分配的连续内存,而采用了下面的算法。但是实际上,这样还是处理不了这种情况。仅仅是个人愚见!!!
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*/
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ngx_os_argv_last= ngx_os_argv[0];
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for (i = 0; ngx_os_argv[i]; i++) {
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if (ngx_os_argv_last == ngx_os_argv[i]) {
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ngx_os_argv_last= ngx_os_argv[i]+ ngx_strlen(ngx_os_argv[i]) + 1;
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}
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}
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for (i = 0; environ[i]; i++) {
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if (ngx_os_argv_last == environ[i]) {
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size= ngx_strlen(environ[i]) + 1;
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ngx_os_argv_last= environ[i]+ size;
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ngx_cpystrn(p, (u_char *) environ[i], size);
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environ[i] = (char *) p;
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p+= size;
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}
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}
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ngx_os_argv_last--;
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return NGX_OK;
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}
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void
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ngx_setproctitle(char *title)
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{
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u_char *p;
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#if (NGX_SOLARIS)
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ngx_int_t i;
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size_t size;
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#endif
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ngx_os_argv[1]= NULL;
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p = ngx_cpystrn((u_char*) ngx_os_argv[0], (u_char*) "nginx: ",
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ngx_os_argv_last- ngx_os_argv[0]);
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p = ngx_cpystrn(p, (u_char *) title, ngx_os_argv_last - (char*) p);
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#if (NGX_SOLARIS)
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size = 0;
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for (i = 0; i < ngx_argc; i++) {
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size+= ngx_strlen(ngx_argv[i]) + 1;
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}
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if (size > (size_t)((char *) p - ngx_os_argv[0])) {
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/*
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* ngx_setproctitle() is too rareoperation so we use
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* the non-optimized copies
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*/
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p = ngx_cpystrn(p, (u_char *) " (",ngx_os_argv_last - (char*) p);
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for (i = 0; i < ngx_argc; i++) {
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p= ngx_cpystrn(p,(u_char *) ngx_argv[i],
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ngx_os_argv_last - (char*) p);
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p= ngx_cpystrn(p,(u_char *) "", ngx_os_argv_last - (char *) p);
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}
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if (*(p - 1) == ' ') {
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*(p- 1) = ')';
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}
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}
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#endif
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if (ngx_os_argv_last - (char*) p) {
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ngx_memset(p, NGX_SETPROCTITLE_PAD,ngx_os_argv_last - (char*) p);
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}
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ngx_log_debug1(NGX_LOG_DEBUG_CORE, ngx_cycle->log, 0,
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"setproctitle:\"%s\"", ngx_os_argv[0]);
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