RSYNC extension

doc/tutorial.rst

@@ -265,7 +265,7 @@ recipe:
 
    FROM almalinux:8
    RUN yum -y install python36
-   RSYNC ./hello.py /
+   COPY ./hello.py /
    RUN chmod 755 /hello.py
 
 These four instructions say:
@@ -275,14 +275,18 @@ These four instructions say:
   2. :code:`RUN`: Install the :code:`python36` RPM package, which we need for
      our Hello World program.
 
-  3. :code:`RSYNC`: Copy the file :code:`hello.py` we just made to the root
+  3. :code:`COPY`: Copy the file :code:`hello.py` we just made to the root
      directory of the image. In the source argument, the path is relative to
-     the *context directory*, which we’ll see more of below. (This instruction
-     is a Charliecloud extension; see :ref:`its documentation <ch-image_rsync>`
-     for details.) You can also use standard :code:`COPY` if you prefer.)
+     the *context directory*, which we’ll see more of below.
 
   4. :code:`RUN`: Make that file executable.
 
+.. note::
+
+   :code:`COPY` is a standard instruction but has a number of disadvantages in
+   its corner cases. Charliecloud also has :code:`RSYNC`, which addresses
+   these; see :ref:`its documentation <ch-image_rsync>` for details.
+
 Let’s build this image::
 
   $ ch-image build -t hello -f Dockerfile .

lib/filesystem.py

@@ -137,6 +137,31 @@ def git_incompatible_p(self):
       "Return True if I can’t be stored in Git because of my name."
       return self.name.startswith(".git")
 
+   @property
+   def is_root(self):
+      return (str(self) == "/")
+
+   @property
+   def mountpoint(self):
+      """Return the mount point of the filesystem containing me (or, if
+         symlink, the file pointed to)."""
+      # https://stackoverflow.com/a/4453715
+      try:
+         pc = self.resolve(strict=True)
+      except RuntimeError:
+         ch.FATAL("not found, can’t resolve: %s" % self)
+      # Unclear whether ismount() deals correctly with the root directory, so
+      # do the stat(2) stuff ourself.
+      dev_child = pc.stat().st_dev
+      while (not pc.is_root):
+         dev_parent = pc.parent.stat().st_dev
+         if (dev_child != dev_parent):
+            return pc
+         pc = pc.parent
+      # Got all the way up to root without finding a transition, so we’re on
+      # the root filesystem.
+      return Path("/")
+
    @property
    def parent(self):
       ret = super().parent
@@ -340,7 +365,7 @@ def is_relative_to(self, *other):
 
    def joinpath_posix(self, right):
       # This method is a hot spot, so the hairiness is due to optimizations.
-      # It runs about 30% faster than the naïve verson below.
+      # It runs about 30% faster than the naïve verson referenced below.
       if (isinstance(right, Path)):
          right_parts = right._parts
          ts_p = right.trailing_slash_p

test/build/55_cache.bats

@@ -906,10 +906,10 @@ EOF
     # Prepare fixtures. These need various manipulating during the test, which
     # is why they’re built here on the fly.
     fixtures=${BATS_TMPDIR}/rsync-cache
-    mkdir -p "$fixtures"
+    rm -Rf --one-file-system "$fixtures"
+    mkdir "$fixtures"
     echo hello > "$fixtures"/file1
-    rm -f "$fixtures"/file1a
-    mkdir -p "$fixtures"/dir1
+    mkdir "$fixtures"/dir1
     touch "$fixtures"/dir1/file1 "$fixtures"/dir1/file2
 
     printf '\n*** Build; all misses.\n\n'