cmd/snap-discard-ns: add support for per-user mount namespaces #6010
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| #!/usr/bin/env python2 | ||
| """ | ||
| Pure-python limited-use wrapper around the mount library function. | ||
| """ | ||
| from __future__ import print_function, absolute_import, unicode_literals | ||
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| from argparse import ArgumentParser | ||
| from ctypes import CDLL, c_char_p, c_long, get_errno | ||
| from ctypes.util import find_library | ||
| from os import strerror | ||
| from sys import stderr | ||
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| __all__ = ('mount', ) | ||
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| class MountOpts(object): | ||
| """MountOpts contain various flags for the mount system call.""" | ||
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| Bind = 4096 | ||
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| def mount(source, target, fstype, flags=0, data=""): | ||
| # type: (unicode, unicode, unicode, int, unicode) -> None | ||
| """mount is a thin wrapper around the mount library function.""" | ||
| libc_name = find_library(b"c") | ||
| if libc_name is None: | ||
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There was a problem hiding this comment. PEP8 suggests testing None the way I did to avoid masking the distinction between None and other things that evaluate to false in boolean context. |
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| raise Exception("cannot find the C library") | ||
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There was a problem hiding this comment. Maybe make that more specific, say There was a problem hiding this comment. I switched error handling, it should work fine as-is now. |
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| libc = CDLL(libc_name, use_errno=True) | ||
| retval = libc.mount( | ||
| c_char_p(source.encode("UTF-8")), | ||
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There was a problem hiding this comment.
There was a problem hiding this comment. UTF-8 is not the default, defaults depend on locale. There was a problem hiding this comment. I think it is in Py3. In Py2 it was derived from your locale or sth. OTOH, I'm not sure we should be forcing utf-8 here which may not be the same as input encoding so the input path provided to the script will be a different byte sequence from one encoded to utf-8. |
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| c_char_p(target.encode("UTF-8")), | ||
| c_char_p(fstype.encode("UTF-8")), | ||
| c_long(flags), | ||
| None if data == "" else c_char_p(data.encode("UTF-8"))) | ||
| if retval < 0: | ||
| errno = get_errno() | ||
| raise OSError(errno, strerror(errno)) | ||
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| def main(): | ||
| # type: () -> None | ||
| parser = ArgumentParser() | ||
| parser.add_argument("source", help="path of the device or bind source") | ||
| parser.add_argument("target", help="path of the new mount point") | ||
| group = parser.add_mutually_exclusive_group(required=True) | ||
| group.add_argument("--bind", action="store_const", const="bind", | ||
| help="create a new mount point of existing path") | ||
| group.add_argument("-t", "--type", help="filesystem type to mount") | ||
| opts = parser.parse_args() | ||
| if opts.bind is not None: | ||
| mount(opts.source, opts.target, b"", MountOpts.Bind) | ||
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There was a problem hiding this comment.
There was a problem hiding this comment. What is the problem with b"".encode('utf-8')? There was a problem hiding this comment.
There was a problem hiding this comment. In python 2 bytes is just a string. It does have the encode method. Having said that I will look at unifying this even though I would much rather not have to use python 2 and all of its quirks at all. There was a problem hiding this comment. What I meant is that if you use the Py2 version of the script in Py3, IIRC There was a problem hiding this comment. Yeah but this was for Python 2 specifically. The Python 3 version did not need that. EDIT, removed part about u"" on Python3. Please look at what I did now, it works and is Mypy-clean on both versions. |
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| else: | ||
| mount(opts.source, opts.target, opts.fstype) | ||
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| if __name__ == "__main__": | ||
| try: | ||
| main() | ||
| except Exception as err: | ||
| print(err, file=stderr) | ||
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There was a problem hiding this comment. Did you forget to There was a problem hiding this comment. I didn't intend to show the traceback but I think I did forget to return the exit status. I will fix this. There was a problem hiding this comment. I think you can then drop the whole try/except block and just call There was a problem hiding this comment. Then you could |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,58 @@ | ||
| #!/usr/bin/env python3 | ||
| """ | ||
| Pure-python limited-use wrapper around the mount library function. | ||
| """ | ||
| from argparse import ArgumentParser | ||
| from ctypes import CDLL, c_char_p, c_long, get_errno | ||
| from ctypes.util import find_library | ||
| from enum import IntEnum | ||
| from os import strerror | ||
| from sys import stderr | ||
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| __all__ = ('mount', ) | ||
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| class MountOpts(IntEnum): | ||
| """MountOpts contain various flags for the mount system call.""" | ||
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| Bind = 4096 | ||
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| def mount(source: str, target: str, fstype: str, flags: int = 0, | ||
| data: str = "") -> None: | ||
| """mount is a thin wrapper around the mount library function.""" | ||
| libc_name = find_library("c") | ||
| if libc_name is None: | ||
| raise Exception("cannot find the C library") | ||
| libc = CDLL(libc_name, use_errno=True) | ||
| retval = libc.mount( | ||
| c_char_p(source.encode("UTF-8")), | ||
| c_char_p(target.encode("UTF-8")), | ||
| c_char_p(fstype.encode("UTF-8")), | ||
| c_long(flags), | ||
| None if data == "" else c_char_p(data.encode("UTF-8"))) | ||
| if retval < 0: | ||
| errno = get_errno() | ||
| raise OSError(errno, strerror(errno)) | ||
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| def main() -> None: | ||
| parser = ArgumentParser() | ||
| parser.add_argument("source", help="path of the device or bind source") | ||
| parser.add_argument("target", help="path of the new mount point") | ||
| group = parser.add_mutually_exclusive_group(required=True) | ||
| group.add_argument("--bind", action="store_const", const="bind", | ||
| help="create a new mount point of existing path") | ||
| group.add_argument("-t", "--type", help="filesystem type to mount") | ||
| opts = parser.parse_args() | ||
| if opts.bind is not None: | ||
| mount(opts.source, opts.target, "", MountOpts.Bind) | ||
| else: | ||
| mount(opts.source, opts.target, opts.fstype) | ||
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| if __name__ == "__main__": | ||
| try: | ||
| main() | ||
| except Exception as err: | ||
| print(err, file=stderr) |
| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,6 @@ | ||
| #!/bin/sh | ||
| if [ "$(command -v python3)" != "" ]; then | ||
| exec ./mount-py3.py "$@"; | ||
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There was a problem hiding this comment. Can we have just one version of the script? The way you've written py2 version, it should work with py3 just fine. There was a problem hiding this comment. I tried to initially but in the end I decided no to. Using one version of the script puts most pressure on the unicode vs string vs bytes across the two versions. Right now both versions are correct but this could be subtly broken with a single script. There was a problem hiding this comment. I think one script is enough. With the exception of |
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| else | ||
| exec ./mount-py2.py "$@"; | ||
| fi | ||
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Should we make sure snap instance name is sane?
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Good point, we probably should. I will make that adjustment.