From 80013e2eae1b635973552bd2c2146f7a352aa4a0 Mon Sep 17 00:00:00 2001
From: Michael Santos <michael.santos@gmail.com>
Date: Sun, 9 Mar 2014 13:06:51 -0400
Subject: [PATCH] Add support for bind mounts using mount(2)

Assuming a the directory "/tmp/mnt" exists:

    1> Port = alcove_drv:start([{exec, "sudo"}]).

    % Fork a process with a new mount namespace
    2> {ok, Child} = alcove:clone(Port, alcove:clone_define(Port, newns)).

    % Read-only bind mount of /bin on /tmp/mnt
    3> alcove:mount(Port, [Child], "/bin", "/tmp/mnt", "", 4096 bxor 1, "").

    % Run "/bin/ls -al /tmp/mnt" in the mount namespace
    4> alcove:execvp(Port, [Child], "/bin/ls", ["/bin/ls", "-al", "/tmp/mnt]).
---
 c_src/alcove_call.proto |  1 +
 c_src/alcove_mount.c    | 96 +++++++++++++++++++++++++++++++++++++++++
 rebar.config            |  1 +
 3 files changed, 98 insertions(+)
 create mode 100644 c_src/alcove_mount.c

diff --git a/c_src/alcove_call.proto b/c_src/alcove_call.proto
index ec332c2..4c973ec 100644
--- a/c_src/alcove_call.proto
+++ b/c_src/alcove_call.proto
@@ -11,6 +11,7 @@ getpid/0
 getrlimit/1
 getuid/0
 kill/2
+mount/5
 pid/0
 rlimit_define/1
 setgid/1
diff --git a/c_src/alcove_mount.c b/c_src/alcove_mount.c
new file mode 100644
index 0000000..55cccbd
--- /dev/null
+++ b/c_src/alcove_mount.c
@@ -0,0 +1,96 @@
+/* Copyright (c) 2014, Michael Santos <michael.santos@gmail.com>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+#include "alcove.h"
+#include "alcove_call.h"
+
+#include <sys/mount.h>
+
+/*
+ * mount(2)
+ *
+ */
+    ETERM *
+alcove_mount(alcove_state_t *ap, ETERM *arg)
+{
+    ETERM *hd = NULL;
+    char *source = NULL;
+    char *target = NULL;
+    char *filesystemtype = NULL;
+    unsigned long mountflags = 0;
+    char *data = NULL;
+
+    int rv = 0;
+
+    /* source */
+    arg = alcove_list_head(&hd, arg);
+    if (!hd || !ALCOVE_IS_IOLIST(hd))
+        goto BADARG;
+
+    if (erl_iolist_length(hd) > 0)
+        source = erl_iolist_to_string(hd);
+
+    if (!source)
+        goto BADARG;
+
+    /* target */
+    arg = alcove_list_head(&hd, arg);
+    if (!hd || !ALCOVE_IS_IOLIST(hd))
+        goto BADARG;
+
+    if (erl_iolist_length(hd) > 0)
+        target = erl_iolist_to_string(hd);
+
+    if (!target)
+        goto BADARG;
+
+    /* filesystemtype */
+    arg = alcove_list_head(&hd, arg);
+    if (!hd || !ALCOVE_IS_IOLIST(hd))
+        goto BADARG;
+
+    if (erl_iolist_length(hd) > 0)
+        filesystemtype = erl_iolist_to_string(hd);
+
+    /* mountflags */
+    arg = alcove_list_head(&hd, arg);
+    if (!hd || !ERL_IS_INTEGER(hd))
+        goto BADARG;
+
+    mountflags = ERL_INT_VALUE(hd);
+
+    /* data */
+    arg = alcove_list_head(&hd, arg);
+    if (!hd || !ALCOVE_IS_IOLIST(hd))
+        goto BADARG;
+
+    if (erl_iolist_length(hd) > 0)
+        data = erl_iolist_to_string(hd);
+
+    rv = mount(source, target, filesystemtype, mountflags, data);
+
+    erl_free(source);
+    erl_free(target);
+    erl_free(filesystemtype);
+    erl_free(data);
+
+    return ( (rv < 0) ? alcove_errno(errno) : erl_mk_atom("ok"));
+
+BADARG:
+    erl_free(source);
+    erl_free(target);
+    erl_free(filesystemtype);
+    erl_free(data);
+    return erl_mk_atom("badarg");
+}
diff --git a/rebar.config b/rebar.config
index 44e4466..f43bd7b 100644
--- a/rebar.config
+++ b/rebar.config
@@ -13,6 +13,7 @@
         "c_src/alcove_exec.c",
         "c_src/alcove_fork.c",
         "c_src/alcove_limit.c",
+        "c_src/alcove_mount.c",
         "c_src/alcove_proc.c",
         "c_src/alcove_utsname.c",