diff --git a/exec.cpp b/exec.cpp
index 8d6cfe043..320bcdd46 100644
--- a/exec.cpp
+++ b/exec.cpp
@@ -1185,7 +1185,7 @@ void exec_job(parser_t &parser, job_t *j)
 
                 // Here we must have a non-NULL block_output_io_buffer
                 assert(block_output_io_buffer.get() != NULL);
-                io_remove(process_net_io_chain, block_output_io_buffer);
+                process_net_io_chain.remove(block_output_io_buffer);
 
                 block_output_io_buffer->read();
 
diff --git a/io.cpp b/io.cpp
index 61af4a9c0..57ce43d3c 100644
--- a/io.cpp
+++ b/io.cpp
@@ -210,11 +210,6 @@ void io_chain_t::append(const io_chain_t &chain)
     this->insert(this->end(), chain.begin(), chain.end());
 }
 
-void io_remove(io_chain_t &list, const shared_ptr<const io_data_t> &element)
-{
-    list.remove(element);
-}
-
 void io_print(const io_chain_t &chain)
 {
     if (chain.empty())
@@ -288,3 +283,4 @@ io_chain_t::io_chain_t(const shared_ptr<io_data_t> &data) :
 io_chain_t::io_chain_t() : std::vector<shared_ptr<io_data_t> >()
 {
 }
+
diff --git a/io.h b/io.h
index 894e4c28c..112d7611c 100644
--- a/io.h
+++ b/io.h
@@ -63,8 +63,9 @@ public:
 class io_fd_t : public io_data_t
 {
 public:
-    /** fd to redirect specified fd to */
+    /** fd to redirect specified fd to. For example, in 2>&1, old_fd is 1, and io_data_t::fd is 2 */
     const int old_fd;
+    
     /** Whether to close old_fd */
     const bool close_old;
 
@@ -195,13 +196,6 @@ public:
     shared_ptr<io_data_t> get_io_for_fd(int fd);
 };
 
-/**
-   Remove the specified io redirection from the chain
-*/
-void io_remove(io_chain_t &list, const shared_ptr<const io_data_t> &element);
-
-/** Destroys an io_chain */
-void io_chain_destroy(io_chain_t &chain);
 
 /**
    Return the last io redirection in the chain for the specified file descriptor.
diff --git a/postfork.cpp b/postfork.cpp
index 713e2247c..80318c473 100644
--- a/postfork.cpp
+++ b/postfork.cpp
@@ -173,10 +173,10 @@ static int handle_child_io(const io_chain_t &io_chain)
     free_redirected_fds_from_pipes(io_chain);
     for (size_t idx = 0; idx < io_chain.size(); idx++)
     {
-        io_data_t *io = io_chain.at(idx).get();
+        const io_data_t *io = io_chain.at(idx).get();
         int tmp;
 
-        if (io->io_mode == IO_FD && io->fd == static_cast<io_fd_t*>(io)->old_fd)
+        if (io->io_mode == IO_FD && io->fd == static_cast<const io_fd_t*>(io)->old_fd)
         {
             continue;
         }
@@ -197,7 +197,7 @@ static int handle_child_io(const io_chain_t &io_chain)
             case IO_FILE:
             {
                 // Here we definitely do not want to set CLO_EXEC because our child needs access
-                CAST_INIT(io_file_t *, io_file, io);
+                CAST_INIT(const io_file_t *, io_file, io);
                 if ((tmp=open(io_file->filename_cstr,
                               io_file->flags, OPEN_MASK))==-1)
                 {
@@ -257,7 +257,7 @@ static int handle_child_io(const io_chain_t &io_chain)
             case IO_BUFFER:
             case IO_PIPE:
             {
-                CAST_INIT(io_pipe_t *, io_pipe, io);
+                CAST_INIT(const io_pipe_t *, io_pipe, io);
                 /* If write_pipe_idx is 0, it means we're connecting to the read end (first pipe fd). If it's 1, we're connecting to the write end (second pipe fd). */
                 unsigned int write_pipe_idx = (io_pipe->is_input ? 0 : 1);
                 /*