Re: Problem with SYS_mount

On  5 May 2008 at 21:14, Sam Joseph wrote:
> I need to mount a loopback file system. I'm using SYS_mount, but it 
> always fails with ENOTDIR. Am I doing something silly? Here's the 
> offending line:
>
> if(syscall(SYS_mount,
>    "/home/sam/mnt/", "/home/sam/myfile.img", "-o loop" ))
>          perror("Mount failure/ ");

There are so many problems with your code and approach that it's hard to
know where to begin!

First of all, the prototype for the system call is
asmlinkage long sys_mount(char __user *dev_name, char __user* dir_name,
  char __user *type, unsigned long flags, void __user *data);

So your code has the first two arguments the wrong way round, and the
last two arguments are missing. The third argument is, unfortunately,
much too naive: while the mount(8) command is happy to accept options
like "-o loop", the mount system call isn't.

But you shouldn't be using the mount system call at all! The mount
program does some other fairly complicated work besides executing a
system call, and you'd need to re-do all that by hand. Why bother? Just
run mount(8).

If you really want to work programatically, you can open one of the loop
devices, perform an ioctl on it (request LOOP_SET_FD with extra argument
"/home/sam/myfile.img"), then use mount(2).