01/02: Simplify remouting with MS_PRIVATE in sandbox build

[Andy Wingo]

wingo pushed a commit to branch master
in repository guix.

commit 842e0e439a22081be1b4fed7ddc21d6d228afd10
Author: Jörg Thalheim <address@hidden>
Date:   Fri Nov 25 00:08:34 2016 +0100

    Simplify remouting with MS_PRIVATE in sandbox build
    
    also fix race condition if mounts are added after mountinfo is read.
---
 nix/libstore/build.cc | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/nix/libstore/build.cc b/nix/libstore/build.cc
index 63540dd..d68e8b2 100644
--- a/nix/libstore/build.cc
+++ b/nix/libstore/build.cc
@@ -2086,12 +2086,8 @@ void DerivationGoal::runChild()
                outside of the namespace.  Making a subtree private is
                local to the namespace, though, so setting MS_PRIVATE
                does not affect the outside world. */
-            Strings mounts = 
tokenizeString<Strings>(readFile("/proc/self/mountinfo", true), "\n");
-            foreach (Strings::iterator, i, mounts) {
-                vector<string> fields = tokenizeString<vector<string> >(*i, " 
");
-                string fs = decodeOctalEscaped(fields.at(4));
-                if (mount(0, fs.c_str(), 0, MS_PRIVATE, 0) == -1)
-                    throw SysError(format("unable to make filesystem `%1%' 
private") % fs);
+            if (mount(0, "/", 0, MS_REC|MS_PRIVATE, 0) == -1) {
+                throw SysError("unable to make ‘/’ private mount");
             }
 
             /* Bind-mount chroot directory to itself, to treat it as a