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

[Torben Hohn]

On Wed, May 22, 2019 at 03:33:43PM +0200, dion at linutronix.de wrote:
> 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'

This is great. But...

Please implement it as a class.

class Excursion(object):
	def __init__(self, path, restore, dst):
		self.path = path
		...
		self.orig_name = None

	def excurse(self, rfs):

		... 
		self.orig_name = "%s.orig" % self.path


	def unexcurse(self, rfs):


This also allows you to store the actual filename you have
used in the object. That would allow this to work later on
even when x.orig is in the way.




> 
> 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
> 
> 
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> elbe-devel at linutronix.de
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-- 
Torben Hohn
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