pack: "fakechroot" engine always creates its store.

Previously it would silently fail to create the /gnu/store symlink when
the host has a read-only /gnu as is the case in these tests.

* gnu/packages/aux-files/run-in-namespace.c (exec_with_loader): Unlink
the ancestor of ORIGINAL_STORE under NEW_ROOT.  Check the return value
of 'symlink' when creating NEW_STORE.
* tests/guix-pack-relocatable.sh: Check the contents of the store as
seen by the wrapped executable, with all three engines, and with both
"/gnu" and "/gnu/store" erased.

2 files changed, 39 insertions, 3 deletions

diff --git a/gnu/packages/aux-files/run-in-namespace.c b/gnu/packages/aux-files/run-in-namespace.c
index 7f7e5c6885..436c0b6286 100644
--- a/gnu/packages/aux-files/run-in-namespace.c
+++ b/gnu/packages/aux-files/run-in-namespace.c
@@ -441,10 +441,23 @@ exec_with_loader (const char *store, int argc, char *argv[])
   char *new_root = mkdtemp (strdup ("/tmp/guix-exec-XXXXXX"));
   mirror_directory ("/", new_root, make_symlink);
 
+  /* 'mirror_directory' created a symlink for the ancestor of ORIGINAL_STORE,
+     typically "/gnu".  Remove that entry so we can create NEW_STORE
+     below.  */
+  const char *slash = strchr (original_store + 1, '/');
+  const char *top = slash != NULL
+    ? strndupa (original_store, slash - original_store)
+    : original_store;
+  char *new_store_top = concat (new_root, top);
+  unlink (new_store_top);
+
+  /* Now create the store under NEW_ROOT.  */
   char *new_store = concat (new_root, original_store);
   char *new_store_parent = dirname (strdup (new_store));
   mkdir_p (new_store_parent);
-  symlink (store, new_store);
+  err = symlink (store, new_store);
+  if (err < 0)
+    assert_perror (errno);
 
 #ifdef GCONV_DIRECTORY
   /* Tell libc where to find its gconv modules.  This is necessary because
diff --git a/tests/guix-pack-relocatable.sh b/tests/guix-pack-relocatable.sh
index 1ba3889036..b8d36a02c6 100644
--- a/tests/guix-pack-relocatable.sh
+++ b/tests/guix-pack-relocatable.sh
@@ -90,7 +90,7 @@ case "`uname -m`" in
 	# Try '-RR' and PRoot.
 	tarball="`guix pack -RR -S /Bin=bin sed`"
 	tar tvf "$tarball" | grep /bin/proot
-	(cd "$test_directory"; tar xvf "$tarball")
+	(cd "$test_directory"; tar xf "$tarball")
 	run_without_store GUIX_EXECUTION_ENGINE="proot" \
 	"$test_directory/Bin/sed" --version > "$test_directory/output"
 	grep 'GNU sed' "$test_directory/output"
@@ -101,6 +101,29 @@ case "`uname -m`" in
 	grep 'GNU sed' "$test_directory/output"
 
 	chmod -Rf +w "$test_directory"; rm -rf "$test_directory"/*
+
+	if unshare -r true
+	then
+	    # Check whether the store contains everything it should.  Check
+	    # once when erasing $STORE_PARENT ("/gnu") and once when erasing
+	    # $NIX_STORE_DIR ("/gnu/store").
+	    tarball="`guix pack -RR -S /bin=bin bash-minimal`"
+	    (cd "$test_directory"; tar xf "$tarball")
+
+	    STORE_PARENT="`dirname $NIX_STORE_DIR`"
+	    export STORE_PARENT
+
+	    for engine in userns proot fakechroot
+	    do
+		for i in $(guix gc -R $(guix build bash-minimal | grep -v -e '-doc$'))
+		do
+		    unshare -mrf sh -c "mount -t tmpfs none \"$NIX_STORE_DIR\"; GUIX_EXECUTION_ENGINE=$engine $test_directory/bin/sh -c 'echo $NIX_STORE_DIR/*'" | grep $(basename $i)
+		    unshare -mrf sh -c "mount -t tmpfs none \"$STORE_PARENT\";  GUIX_EXECUTION_ENGINE=$engine $test_directory/bin/sh -c 'echo $NIX_STORE_DIR/*'" | grep $(basename $i)
+		done
+	    done
+
+	    chmod -Rf +w "$test_directory"; rm -rf "$test_directory"/*
+	fi
 	;;
     *)
 	echo "skipping PRoot and Fakechroot tests" >&2
@@ -109,7 +132,7 @@ esac
 
 # Ensure '-R' works with outputs other than "out".
 tarball="`guix pack -R -S /share=share groff:doc`"
-(cd "$test_directory"; tar xvf "$tarball")
+(cd "$test_directory"; tar xf "$tarball")
 test -d "$test_directory/share/doc/groff/html"
 
 # Ensure '-R' applies to propagated inputs.  Failing to do that, it would fail