如何使用 ANSI C 檢查文件是否可執行？

Question

我正在嘗試編寫一個程序來檢查目錄中的文件。 創建新文件時，我必須檢查它是否可執行，如果是，我必須執行它。

我正在使用 inotify 接口並且它運行良好，但是當我嘗試使用 stat(2) 檢查文件是否可執行時遇到了一些問題。 我發現我沒有執行它的權限。

是否將我要檢查的目錄的絕對路徑傳遞給程序創建權限問題？

int main(int argc,char * argv []){

int fd,wd,len,i=0;
char buffer [EVENT_SIZE_BUF];

if(argc != 2)
    usage();

if((fd = inotify_init()) == -1)
    perror("inotify_init()");   


if((wd = inotify_add_watch(fd,argv[1],IN_CREATE) -1))
    perror("inotify_add_watch()");

while(1){


    if((len = read(fd,buffer,EVENT_SIZE_BUF)) < 0)
        perror("read()");

    struct inotify_event * ev = (struct inotify_event *)&buffer;

    if(ev->len > 0){

        if(ev->mask & IN_CREATE && ((ev-> mask & IN_ISDIR) == 0x00)){

            printf("SPY; new file is created %s\n",ev->name);

            char * path = strcat(argv[1],ev->name);
            printf("%s\n",path);

            struct stat sb;

            if(!stat(path,&sb)){

                printf( (S_ISDIR(sb.st_mode)) ? "d" : "-");
                printf( (sb.st_mode & S_IRUSR) ? "r" : "-");
                printf( (sb.st_mode & S_IWUSR) ? "w" : "-");
                printf( (sb.st_mode & S_IXUSR) ? "x" : "-");
                printf( (sb.st_mode & S_IRGRP) ? "r" : "-");
                printf( (sb.st_mode & S_IWGRP) ? "w" : "-");
                printf( (sb.st_mode & S_IXGRP) ? "x" : "-");
                printf( (sb.st_mode & S_IROTH) ? "r" : "-");
                printf( (sb.st_mode & S_IWOTH) ? "w" : "-");
                printf( (sb.st_mode & S_IXOTH) ? "x" : "-");
                fflush(stdout);
                printf("\n");
            }




        }else{ printf("dir\n"); }
    }               
}

inotify_rm_watch(fd,wd);
close(fd);
return 0;
}

Answer 1

您使用的是 linux，因此您可以使用access()函數

if (access("/my/file", X_OK) != -1) {
    printf("execution permission enabled\n");
} else {
    printf("execution permission disabled\n");
}

Answer 2

你在解決倫佐·達沃利的練習嗎？ :)

但是，我像你一樣被困住了，我發現使用 Nautilus 復制可執行文件，它會創建一個“可執行文件（復制）”，並使用stat()或access()返回 X-Permission 錯誤。

用 cp cp exe1 exe2復制它有效！！

這是我的代碼：

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/inotify.h>
#include <sys/stat.h>

#define _GNU_SOURCE 
#define EVENT_SIZE  ( sizeof (struct inotify_event) )
#define EVENT_BUF_LEN     ( 1024 * ( EVENT_SIZE + 16 ) )

void main(int argc, char **argv){

int fd, wd, length, i=0;
char buffer[EVENT_BUF_LEN];

char* dir = argv[1];

/*creating the INOTIFY instance*/
if((fd = inotify_init()) < 0)
    perror( "inotify_init" );


/*adding the directory into watch list. 
Here, the suggestion is to validate the existence of the directory before adding into monitoring list.*/
wd = inotify_add_watch( fd, dir, IN_CREATE | IN_DELETE );

while(1) {

    i=0;
    pid_t p;
    struct stat st;

    /*read to determine the event change happens on “/tmp” directory. Actually this read blocks until the change event occurs*/ 
    if((length = read(fd, buffer, EVENT_BUF_LEN )) < 0)
        perror( "read" );
    /*actually read return the list of change events happens. Here, read the change event one by one and process it accordingly.*/
    while ( i < length ){     
        struct inotify_event *event = ( struct inotify_event * ) &buffer[ i ];     
        if ( event->len ) {
            if ( event->mask & IN_CREATE ) {
                if ( event->mask & IN_ISDIR )
                    printf("New directory %s created.\n", event->name );
                else{
                    printf("New file %s created.\n", event->name );
                    char* file_name;
                    asprintf(&file_name, "%s/%s", dir, event->name);

                    printf("Check if %s is executable\n", file_name);
                    if (access(file_name, X_OK) == 0){ //If file is executable
                        printf("Executable file! Call fork()\n");
                        if ((p = fork()) == 0) {  // Child process: do your work here
                            if (execlp(file_name, file_name,  (char*) 0)<0)
                                fprintf(stderr, "execlp error\n");
                            exit(0);
                        }
                        else{
                            while(waitpid(p, NULL, WNOHANG) != p);
                            remove (event->name);
                            printf("%s done & gone\n", event->name);
                        }
                    }
                    else
                        fprintf(stderr, "Not executable file\n");
                }
            }
            else if ( event->mask & IN_DELETE ) {
                if ( event->mask & IN_ISDIR ) 
                    printf( "Directory %s deleted.\n", event->name );
                else
                    printf( "File %s deleted.\n", event->name );
            }
        }

        i += EVENT_SIZE + event->len;
    }
}

/*removing the “/tmp” directory from the watch list.*/
inotify_rm_watch( fd, wd );

/*closing the INOTIFY instance*/
close( fd );

 }

Answer 3

這在 ANSI C 中是不可能的，你需要 POSIX。