Synchronise parent/child in callcmd()

Prevent poll() from running before all file descriptors are set up
and debug logging is disabled in the child.

Signed-off-by: Tobias Ulmer <tu@emlix.com>

diff --git a/generic/e2lib.lua b/generic/e2lib.lua
index 34b5e8b5118d1ee9077d3f10c69dbc76bbff7d6e..eb6e54073723f9dffdee36bb997dee42b6f88ffd 100644 (file)
--- a/generic/e2lib.lua
+++ b/generic/e2lib.lua
@@ -219,7 +219,6 @@ end
 -- @param fdvec Vector of file descriptors (table of numbers).
 -- @return Returns 0 on timeout, < 0 on error and > 0 for the position in fdvec
 -- that has an event waiting.
-
 -- @return True if it's a POLLIN event.
 -- @return True if it's a POLLOUT event.
 function e2lib.poll(timeout, fdvec)
@@ -1224,20 +1223,99 @@ function e2lib.callcmd(argv, fdctv, workdir, envdict)
         return true
     end
 
+    local function sync_pipe_setup()
+        local sync_pipes = {}
+
+        sync_pipes[1], sync_pipes[2] = eio.pipe()
+        if not sync_pipes[1] then
+            return false, sync_pipes[2]
+        end
+
+        sync_pipes[3], sync_pipes[4] = eio.pipe()
+        if not sync_pipes[3] then
+            return false, sync_pipes[4]
+        end
+
+        return sync_pipes
+    end
+
+    local function sync_child(sync_pipes)
+        local rc, re
+
+        -- ping parent
+        rc, re = eio.fwrite(sync_pipes[4], "c")
+        if not rc then
+            return false, re
+        end
+
+        -- wait for parent
+        rc, re = eio.fgetc(sync_pipes[1])
+        if not rc then
+            return false, re
+        elseif rc ~= "p" then
+            return false, err.new("unexpected reply from parent: %q", rc)
+        end
+
+        -- cleanup
+        for _,pfo in ipairs(sync_pipes) do
+            rc, re = eio.fclose(pfo)
+            if not rc then
+                return false, re
+            end
+        end
+
+        return true
+    end
+
+    local function sync_parent(sync_pipes)
+        local rc, re
+
+        -- ping child
+        rc, re = eio.fwrite(sync_pipes[2], "p")
+        if not rc then
+            return false, re
+        end
+
+        -- wait for child
+        rc, re = eio.fgetc(sync_pipes[3])
+        if not rc then
+            return false, re
+        elseif rc ~= "c" then
+            return false, err.new("unexpected reply from child: %q", rc)
+        end
+
+        -- cleanup
+        for _,pfo in ipairs(sync_pipes) do
+            rc, re = eio.fclose(pfo)
+            if not rc then
+                return false, re
+            end
+        end
+
+        return true
+    end
+
     -- start of callcmd() proper
 
     local rc, re, pid
+    local sync_pipes = {}
 
     rc, re = fd_parent_setup(fdctv)
     if not rc then
         return false, re
     end
 
+    sync_pipes, re = sync_pipe_setup()
+    if not sync_pipes then
+        return false, re
+    end
+
     pid, re = e2lib.fork()
     if not pid then
         return false, re
     elseif pid == 0 then
-        -- disable debug logging to console in the child because output mixes
+        -- disable debug logging to console in the child because it
+        -- potentially mixes with the output of the command
         e2lib.setlog(4, false)
 
         fd_child_setup(fdctv)
@@ -1258,6 +1336,11 @@ function e2lib.callcmd(argv, fdctv, workdir, envdict)
             end
         end
 
+        rc, re = sync_child(sync_pipes)
+        if not rc then
+            e2lib.abort(re)
+        end
+
         rc, re = e2lib.execvp(argv[1], argv)
         e2lib.abort(re)
     end
@@ -1267,6 +1350,11 @@ function e2lib.callcmd(argv, fdctv, workdir, envdict)
         return false, re
     end
 
+    rc, re = sync_parent(sync_pipes)
+    if not rc then
+        return false, re
+    end
+
     rc, re = fd_parent_poll(fdctv)
     if not rc then
         return false, re