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9bfb48c921
Summary: Update the copyright & license headers in Python files to reflect the relicensing to GPLv2 Reviewed By: wez Differential Revision: D15487088 fbshipit-source-id: 9f2138dff41048d2c35f15e09a04ae5a9c9c80dd
109 lines
3.8 KiB
Python
109 lines
3.8 KiB
Python
#!/usr/bin/env python3
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#
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# Copyright (c) Facebook, Inc. and its affiliates.
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#
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# This software may be used and distributed according to the terms of the
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# GNU General Public License version 2.
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import ctypes
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import mmap
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import os
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import subprocess
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from ctypes import c_int, c_size_t, c_ssize_t, c_void_p
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from .lib import testcase
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# python's mmap does not allow mapping larger than the file's size
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libc = ctypes.CDLL("libc.so.6")
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c_off_t = c_ssize_t
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libc.mmap.argtypes = [c_void_p, c_size_t, c_int, c_int, c_off_t]
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libc.mmap.restype = ctypes.POINTER(ctypes.c_byte)
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libc.munmap.restype = c_void_p
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libc.munmap.argtypes = [c_void_p, c_size_t]
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@testcase.eden_repo_test
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class MmapTest(testcase.EdenRepoTest):
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contents = "abcdef"
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filename: str
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def populate_repo(self) -> None:
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self.repo.write_file("filename", self.contents)
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self.repo.commit("Initial commit.")
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self.filename = os.path.join(self.mount, "filename")
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def test_mmap_in_backed_file_is_null_terminated(self) -> None:
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fd = os.open(self.filename, os.O_RDONLY)
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try:
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size = os.fstat(fd).st_size
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self.assertEqual(len(self.contents), size)
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map_size = (size + 4095) // 4096 * 4096
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self.assertNotEqual(size, map_size)
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m = libc.mmap(None, map_size, mmap.PROT_READ, mmap.MAP_PRIVATE, fd, 0)
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try:
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# assert the additional mapped bytes are null, per `man 2 mmap`
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for i in range(size, map_size):
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self.assertEqual(0, m[i])
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finally:
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libc.munmap(m, map_size)
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finally:
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os.close(fd)
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def test_mmap_is_null_terminated_after_truncate_and_write_to_overlay(self) -> None:
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# WARNING: This test is very fiddly.
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# The bug is that if a file in Eden is opened with O_TRUNC followed by
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# a series of writes, then mmap of that file with a size larger than the
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# file (but still within the trailing page) does not zero the trailing
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# bytes. Clang relies on this mmap behavior to enforce that the buffer
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# is null-terminated. Since the buffer ends up not being null-
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# terminated, Clang segfaults.
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#
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# It seems like this is a kernel or FUSE bug more than an Eden bug,
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# but we should verify nonetheless that it does not occur.
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# If this test uses the same file committed in populate_repo, the bug
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# does not reproduce.
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filename = os.path.join(self.mount, "filename2")
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# Write to the file from another process. if this process writes the
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# file, the bug is not reproduced.
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subprocess.check_call(
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["dd", "if=/dev/urandom", "of=" + filename, "bs=4096", "count=6"]
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)
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# A few pages, with data slightly beyond a page boundary.
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new_contents = b"abcd" * 3072 + b"abcdef"
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new_size = len(new_contents)
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# Write to the file with another process. if this process writes the
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# file, the bug is not reproduced.
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with subprocess.Popen(
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["dd", "of=" + filename, "bs=512"], stdin=subprocess.PIPE
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) as p:
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p.stdin.write(new_contents)
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fd = os.open(filename, os.O_RDONLY)
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try:
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size = os.fstat(fd).st_size
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self.assertEqual(new_size, size)
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# Map all the way up to a page boundary.
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map_size = (size + 4095) // 4096 * 4096
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self.assertNotEqual(size, map_size)
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m = libc.mmap(None, map_size, mmap.PROT_READ, mmap.MAP_PRIVATE, fd, 0)
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try:
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# Assert the additional mapped bytes are null, per `man 2 mmap`
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for i in range(size, map_size):
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self.assertEqual(0, m[i])
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finally:
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libc.munmap(m, map_size)
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finally:
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os.close(fd)
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