Hi, I'm trying to use CFFI in order to wrap execve (2). The wrapper also uses fork (2) and wait (2). While I have absolutely no problems with execve or fork I'm stumbling on a problem with wait.
Wait takes a pointer to an int to store child process' status. The
problem is: after the call to wait the value stored in the pointer is
the same as before the call.
I am using CFFI 0.10.5 and GNU CLISP 2.47 on Fedora 13.
The code follows:
(defcfun ("fork" c-fork) :int)
(defcfun ("execve" c-execve) :int (filename :string) (args :pointer) (env
:pointer))
(defcfun ("wait" c-wait) :int (status :pointer))
(defun execute-program (path argv env)
(let ((child-pid (c-fork)))
(if (= child-pid -1)
(error "Unable to create child process")
(if (= child-pid 0)
;; Child
(progn
;; Remember: (nth 0 argv) must be the full path to the executable.
(let ((c-argv (foreign-alloc :string :initial-contents (append
(list path) argv)
:null-terminated-p t))
(c-env (foreign-alloc :string :initial-contents env
:null-terminated-p t)))
(c-execve path c-argv c-env)
(foreign-free c-argv)
(foreign-free c-env)))
;; Parent code
(progn
(let ((wait-status (foreign-alloc :int)))
(c-wait wait-status)
;; This test condition is a reimplementation of __WIFEXITED
macro defined at
;; /usr/include/bits/waitstatus.h
(if (= 0 (logand (mem-ref wait-status :int) #x7f))
;; This test condition is a reimplementation of
__WEXITSTATUS macro defined at
;; /usr/include/bits/waitstatus.h
(when (/= 0 (ash (logand (mem-ref wait-status :int) #xff00)
-8))
(error "Child returned an error"))
(error "Failed to execute child process"))
(foreign-free wait-status)))))))
--
Lorenzo Villani <lvill...@binaryhelix.net>
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