Add prefork and preexec support to luxio.subprocess.spawn

1 files changed, 32 insertions, 1 deletions

diff --git a/luxio/subprocess.lua b/luxio/subprocess.lua
index 3da5993..617d20b 100644
--- a/luxio/subprocess.lua
+++ b/luxio/subprocess.lua
@@ -48,6 +48,13 @@
 -- If you want to change directory before exec in the child, you can pass
 -- cwd="/some/path".
 --
+-- To run some code before forking, pass prefork=somefunction and to
+-- run code before exec (in the child) pass preexec=somefunction.
+--
+-- If the prefork function raises an error then the spawn will be stopped and
+-- the error propagated.  If the preexec function raises an error then the exec
+-- will be stopped and the child will exit with status code 1.
+--
 -- spawn_simple has one additional tweak.  If 'stdin' is provided as
 -- a string then it will automatically write that string to the stdin
 -- of the child (and close the FD afterwards) for you automatically.
@@ -100,6 +107,7 @@ local stderr_fh = sio.stderr
 local setenv = l.setenv
 local unsetenv = l.unsetenv
 local _exit = l._exit
+local _TRACEBACK = debug.traceback
 
 local F_SETFD = l.F_SETFD
 local F_GETFD = l.F_GETFD
@@ -236,6 +244,21 @@ local function _spawn(t)
 
    -- Finally, let's fork
 
+   if proc.args.prefork then
+      local ok, msg = xpcall(proc.args.prefork, function(...)
+	 for fd in pairs(parent_close) do
+	    close(fd)
+	 end
+	 for fd in pairs(child_close) do
+	    close(fd)
+	 end
+	 return _TRACEBACK(...)
+      end)
+      if not ok then
+	 error(msg)
+      end
+   end
+
    local pid, errno = fork()
 
    _assert(pid > -1, "Unable to fork()")
@@ -305,7 +328,15 @@ local function _spawn(t)
 	 local cwd = tostring(proc.args.cwd)
 	 local ret, err = chdir(cwd)
 	 if ret ~= 0 then
-	    stderr_fh:write("chdir(" .. cwd .. "): " .. err)
+	    stderr_fh:write("chdir(" .. cwd .. "): " .. err .. "\n")
+	    _exit(1)
+	 end
+      end
+
+      if proc.args.preexec then
+	 local ok, msg = xpcall(proc.args.preexec, _TRACEBACK)
+	 if not ok then
+	    stderr_fh:write(msg .. "\n")
 	    _exit(1)
 	 end
       end