Re: Determining a file's unix file descriptor int value from its pathname?

Denis Papathanasiou wrote:
> I'm experimenting with alien objects to get my lisp app to use the
> unix native fcntl function for file locking.
>
> Following the example in "Advanced Programming in the UNIX
> Environment" book (http://apuebook.com/), I've built the lockfile.o
> object file.
>
> Its function call is: int lockfile(int fd) where fd is the integer
> representation of the file, as the unix os knows it.
>
> Inside my lisp code, I'm able load the object file by calling
> (ext:load-foreign "lockfile.o") and I'm all set to invoke the lockfile
> function with the (def-alien-routine) macro.
>
> But now, I need to pass it an integer (fd) which represents the unix
> file descriptor.
>
> All I have, though, is the lisp pathname object.
>
> Is there a way to convert pathname to the correct integer value?
>
The lockfile wants an fd, which, AFAIK, only exists AFTER you open the 
file.  So you have to open the file in Lisp too, via, with-open-file or 
open or whatever.  This will produce a fd-stream object and then you can 
use sys:fd-stream-fd to get the fd associated with that file.

Ray