Create new system-call in xv6 that returns data about an open files for all running processes

问题

Im started to learn about xv6. And I'm trying to add a new system call that will print the list of open files for all running processes. It has to print pid of each process, its file descriptor number (0,1,2- for each pid), if the file is regular or piped and if the file is readable of writable.

So I know is how to get the pid. Here is an example of a code:

struct proc *p;
    sti();
    acquire(&ptable.lock);
    cprintf("name \t pid \t type \t \n");
    for (p=ptable.proc; p<&ptable.proc[NPROC]; p++){
        cprintf("%s \t %d  \n", p->name, p->pid);
        }
    }
    release (&ptable.lock);

What I don't know and couldn't find on the internet is how to check if file named by file descriptor is writable\riadable\both And I don't know how to check if the type of the file named by file descriptor is pipe\regular.

I looked at file.h and there are fields like type(FD_NONE, FD_PIPE, FD_INODE), char readable,char writable. But I dont understand how to get them...

If you have any resources with subtitle info to share with me or if you can help, I would be happy to hear. Thanks a lot!

回答1:

Check out

struct proc in proc.h
functions in file.c

You should be able to get a pointer to the beginning of the open files array like this:

struct file* fp = (struct file*) &p->ofile;

From there, you can copy the same syntax from the ptable loop to loop through the files. And to check if a file is readable, functions in file.c just check the readable flag:

if(fp->readable && fp->type == FD_PIPE)
 // do some logic

来源：https://stackoverflow.com/questions/61914398/create-new-system-call-in-xv6-that-returns-data-about-an-open-files-for-all-runn

标签

system-calls

xv6