[elbe-devel] [PATCH v1 3/8] Add save excursion in ChRootFilesystem context

[dion at linutronix.de]

From: Olivier Dion <dion at linutronix.de>

Instead of manually copying/moving/deleting files around,
the '__enter__' method of 'ChRootFilesystem' should save the
excursion into 'self.excursion'.

The excursion can be hardcoded directly at the top of the
'__enter__' method.  Depending on the filesystem object,
other files can be add to the excursion as well dynamically.

To put a file into the excursion, 2 variables must be
provide and 1 optional.

* 'path' - file on the *host* to copy to the RFS.
* 'restore' - if to restore 'path' in the RFS on '__exit__'
* 'dst' (optional) - Copy 'path' to 'dst'

If 'dst' is not provided, then 'path' is copy to the same
place in the RFS.

Uppon exiting the 'ChrootFilesystem' context with '__exit__'
the excursion is restored according to the policies in it.
Finally, the excursion is deleted so it's reset in the next
context.

Examples
========

````````````````````````````````````````````````````````````
self.excursion.append({
    "path":"/usr/bin",
    "restore":True
})
````````````````````````````````````````````````````````````

On '__enter__'

* Move "/rfs/usr/bin" to "/rfs/usr/bin.orig", even if it's a
  broken link

* Copy "/usr/bin" to "/rfs/usr/bin"

On '__exit__'

* Remove "/rfs/usr/bin"

* Move "/rfs/usr/bin.orig" to "/rfs/usr/bin"

````````````````````````````````````````````````````````````
ui = "/usr/share/elbe/qemu-elbe/elbe"
self.excursion.append({
    "path":ui,
    "to":"/usr/bin",
    "restore":False
})
````````````````````````````````````````````````````````````

On '__enter__'

* Move "/usr/share/elbe/qemu-elbe/elbe" to "/rfs/usr/bin/elbe"

On '__exit__'

* Remove "/rfs/usr/bin/elbe"

Signed-off-by: Olivier Dion <dion at linutronix.de>
---
 elbepack/efilesystem.py | 73 ++++++++++++++++++++++++++-----------------------
 1 file changed, 39 insertions(+), 34 deletions(-)

diff --git a/elbepack/efilesystem.py b/elbepack/efilesystem.py
index 1f6428e0..3422b6fc 100644
--- a/elbepack/efilesystem.py
+++ b/elbepack/efilesystem.py
@@ -179,32 +179,44 @@ class ChRootFilesystem(ElbeFilesystem):
         os.close(self.cwd)
 
     def __enter__(self):
+        self.excursion = [
+            {"path":"/etc/resolv.conf", "restore":True},
+            {"path":"/etc/apt/apt.conf", "restore":True},
+            {"path":"/usr/sbin/policy-rc.d", "restore":False}
+        ]
+
         if self.interpreter:
             if not self.exists("usr/bin"):
+                if self.islink("usr/bin"):
+                    self.excursion.append({
+                        "path":"/usr/bin",
+                        "restore":True
+                    })
                 self.mkdir("usr/bin")
 
             ui = "/usr/share/elbe/qemu-elbe/" + self.interpreter
             if not os.path.exists(ui):
                 ui = "/usr/bin/" + self.interpreter
-            os.system('cp %s %s' % (ui, self.fname("usr/bin")))
-
-        if self.exists("/etc/resolv.conf"):
-            os.system('mv %s %s' % (self.fname("etc/resolv.conf"),
-                                    self.fname("etc/resolv.conf.orig")))
-        os.system('cp %s %s' % ("/etc/resolv.conf",
-                                self.fname("etc/resolv.conf")))
 
-        if self.exists("/etc/apt/apt.conf"):
-            os.system('cp %s %s' % (self.fname("/etc/apt/apt.conf"),
-                                    self.fname("/etc/apt/apt.conf.orig")))
-        if os.path.exists("/etc/apt/apt.conf"):
-            os.system('cp %s %s' % ("/etc/apt/apt.conf",
-                                    self.fname("/etc/apt/")))
+            self.excursion.append({
+                "path":ui,
+                "dst": "/usr/bin",
+                "restore":False
+            })
+
+        for tmp in self.excursion:
+            origin = tmp["path"]
+            if self.lexists(origin) and tmp["restore"] is True:
+                save_to = "%s.orig" % origin
+                os.system('mv %s %s' % (self.fname(origin), self.fname(save_to)))
+            if os.path.exists(origin):
+                dst = origin
+                if "dst" in tmp:
+                    dst = tmp["dst"]
+                os.system('cp %s %s' % (origin, self.fname(dst)))
 
         self.mkdir_p("usr/sbin")
-        self.write_file("usr/sbin/policy-rc.d",
-                        0o755, "#!/bin/sh\nexit 101\n")
-
+        self.write_file("usr/sbin/policy-rc.d", 0o755, "#!/bin/sh\nexit 101\n")
         self.mount()
         return self
 
@@ -212,25 +224,18 @@ class ChRootFilesystem(ElbeFilesystem):
         if self.inchroot:
             self.leave_chroot()
         self.umount()
-        if self.interpreter:
-            os.system('rm -f %s' %
-                      os.path.join(self.path, "usr/bin/" + self.interpreter))
-
-        os.system('rm -f %s' % (self.fname("etc/resolv.conf")))
-
-        if self.exists("/etc/resolv.conf.orig"):
-            os.system('mv %s %s' % (self.fname("etc/resolv.conf.orig"),
-                                    self.fname("etc/resolv.conf")))
-
-        if self.exists("/etc/apt/apt.conf"):
-            os.system('rm -f %s' % (self.fname("etc/apt/apt.conf")))
-
-        if self.exists("/etc/apt/apt.conf.orig"):
-            os.system('mv %s %s' % (self.fname("etc/apt/apt.conf.orig"),
-                                    self.fname("etc/apt/apt.conf")))
 
-        if self.exists("/usr/sbin/policy-rc.d"):
-            os.system('rm -f %s' % (self.fname("usr/sbin/policy-rc.d")))
+        for tmp in self.excursion:
+            origin = tmp["path"]
+            saved_to = "%s.orig" % origin
+            if self.lexists(origin):
+                flags = "-f"
+                if self.isdir(origin):
+                    flags += "r"
+                os.system('rm %s %s' % (flags, self.fname(origin)))
+            if tmp["restore"] is True and self.lexists(saved_to):
+                os.system('mv %s %s' % (self.fname(saved_to), self.fname(origin)))
+        del self.excursion
 
     def mount(self):
         if self.path == '/':
-- 
2.11.0