Mercurial > hg
view tests/f @ 46607:e9901d01d135
revlog: add a mechanism to verify expected file position before appending
If someone uses `hg debuglocks`, or some non-hg process writes to the .hg
directory without respecting the locks, or if the repo's on a networked
filesystem, it's possible for the revlog code to write out corrupted data.
The form of this corruption can vary depending on what data was written and how
that happened. We are in the "networked filesystem" case (though I've had users
also do this to themselves with the "`hg debuglocks`" scenario), and most often
see this with the changelog. What ends up happening is we produce two items
(let's call them rev1 and rev2) in the .i file that have the same linkrev,
baserev, and offset into the .d file, while the data in the .d file is appended
properly. rev2's compressed_size is accurate for rev2, but when we go to
decompress the data in the .d file, we use the offset that's recorded in the
index file, which is the same as rev1, and attempt to decompress
rev2.compressed_size bytes of rev1's data. This usually does not succeed. :)
When using inline data, this also fails, though I haven't investigated why too
closely. This shows up as a "patch decode" error. I believe what's happening
there is that we're basically ignoring the offset field, getting the data
properly, but since baserev != rev, it thinks this is a delta based on rev
(instead of a full text) and can't actually apply it as such.
For now, I'm going to make this an optional component and default it to entirely
off. I may increase the default severity of this in the future, once I've
enabled it for my users and we gain more experience with it. Luckily, most of my
users have a versioned filesystem and can roll back to before the corruption has
been written, it's just a hassle to do so and not everyone knows how (so it's a
support burden). Users on other filesystems will not have that luxury, and this
can cause them to have a corrupted repository that they are unlikely to know how
to resolve, and they'll see this as a data-loss event. Refusing to create the
corruption is a much better user experience.
This mechanism is not perfect. There may be false-negatives (racy writes that
are not detected). There should not be any false-positives (non-racy writes that
are detected as such). This is not a mechanism that makes putting a repo on a
networked filesystem "safe" or "supported", just *less* likely to cause
corruption.
Differential Revision: https://phab.mercurial-scm.org/D9952
author | Kyle Lippincott <spectral@google.com> |
---|---|
date | Wed, 03 Feb 2021 16:33:10 -0800 |
parents | c102b704edb5 |
children | 6000f5b25c9b |
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#!/usr/bin/env python3 """ Utility for inspecting files in various ways. This tool is like the collection of tools found in a unix environment but are cross platform and stable and suitable for our needs in the test suite. This can be used instead of tools like: [ dd find head hexdump ls md5sum readlink sha1sum stat tail test readlink.py md5sum.py """ from __future__ import absolute_import import binascii import glob import hashlib import optparse import os import re import sys # Python 3 adapters ispy3 = sys.version_info[0] >= 3 if ispy3: def iterbytes(s): for i in range(len(s)): yield s[i : i + 1] else: iterbytes = iter def visit(opts, filenames, outfile): """Process filenames in the way specified in opts, writing output to outfile.""" for f in sorted(filenames): isstdin = f == '-' if not isstdin and not os.path.lexists(f): outfile.write(b'%s: file not found\n' % f.encode('utf-8')) continue quiet = opts.quiet and not opts.recurse or isstdin isdir = os.path.isdir(f) islink = os.path.islink(f) isfile = os.path.isfile(f) and not islink dirfiles = None content = None facts = [] if isfile: if opts.type: facts.append(b'file') if any((opts.hexdump, opts.dump, opts.md5, opts.sha1, opts.sha256)): with open(f, 'rb') as fobj: content = fobj.read() elif islink: if opts.type: facts.append(b'link') content = os.readlink(f).encode('utf8') elif isstdin: content = getattr(sys.stdin, 'buffer', sys.stdin).read() if opts.size: facts.append(b'size=%d' % len(content)) elif isdir: if opts.recurse or opts.type: dirfiles = glob.glob(f + '/*') facts.append(b'directory with %d files' % len(dirfiles)) elif opts.type: facts.append(b'type unknown') if not isstdin: stat = os.lstat(f) if opts.size and not isdir: facts.append(b'size=%d' % stat.st_size) if opts.mode and not islink: facts.append(b'mode=%o' % (stat.st_mode & 0o777)) if opts.links: facts.append(b'links=%d' % stat.st_nlink) if opts.newer: # mtime might be in whole seconds so newer file might be same if stat.st_mtime >= os.stat(opts.newer).st_mtime: facts.append( b'newer than %s' % opts.newer.encode('utf8', 'replace') ) else: facts.append( b'older than %s' % opts.newer.encode('utf8', 'replace') ) if opts.md5 and content is not None: h = hashlib.md5(content) facts.append(b'md5=%s' % binascii.hexlify(h.digest())[: opts.bytes]) if opts.sha1 and content is not None: h = hashlib.sha1(content) facts.append( b'sha1=%s' % binascii.hexlify(h.digest())[: opts.bytes] ) if opts.sha256 and content is not None: h = hashlib.sha256(content) facts.append( b'sha256=%s' % binascii.hexlify(h.digest())[: opts.bytes] ) if isstdin: outfile.write(b', '.join(facts) + b'\n') elif facts: outfile.write(b'%s: %s\n' % (f.encode('utf-8'), b', '.join(facts))) elif not quiet: outfile.write(b'%s:\n' % f.encode('utf-8')) if content is not None: chunk = content if not islink: if opts.lines: if opts.lines >= 0: chunk = b''.join(chunk.splitlines(True)[: opts.lines]) else: chunk = b''.join(chunk.splitlines(True)[opts.lines :]) if opts.bytes: if opts.bytes >= 0: chunk = chunk[: opts.bytes] else: chunk = chunk[opts.bytes :] if opts.hexdump: for i in range(0, len(chunk), 16): s = chunk[i : i + 16] outfile.write( b'%04x: %-47s |%s|\n' % ( i, b' '.join(b'%02x' % ord(c) for c in iterbytes(s)), re.sub(b'[^ -~]', b'.', s), ) ) if opts.dump: if not quiet: outfile.write(b'>>>\n') outfile.write(chunk) if not quiet: if chunk.endswith(b'\n'): outfile.write(b'<<<\n') else: outfile.write(b'\n<<< no trailing newline\n') if opts.recurse and dirfiles: assert not isstdin visit(opts, dirfiles, outfile) if __name__ == "__main__": parser = optparse.OptionParser("%prog [options] [filenames]") parser.add_option( "-t", "--type", action="store_true", help="show file type (file or directory)", ) parser.add_option( "-m", "--mode", action="store_true", help="show file mode" ) parser.add_option( "-l", "--links", action="store_true", help="show number of links" ) parser.add_option( "-s", "--size", action="store_true", help="show size of file" ) parser.add_option( "-n", "--newer", action="store", help="check if file is newer (or same)" ) parser.add_option( "-r", "--recurse", action="store_true", help="recurse into directories" ) parser.add_option( "-S", "--sha1", action="store_true", help="show sha1 hash of the content", ) parser.add_option( "", "--sha256", action="store_true", help="show sha256 hash of the content", ) parser.add_option( "-M", "--md5", action="store_true", help="show md5 hash of the content" ) parser.add_option( "-D", "--dump", action="store_true", help="dump file content" ) parser.add_option( "-H", "--hexdump", action="store_true", help="hexdump file content" ) parser.add_option( "-B", "--bytes", type="int", help="number of characters to dump" ) parser.add_option( "-L", "--lines", type="int", help="number of lines to dump" ) parser.add_option( "-q", "--quiet", action="store_true", help="no default output" ) (opts, filenames) = parser.parse_args(sys.argv[1:]) if not filenames: filenames = ['-'] visit(opts, filenames, getattr(sys.stdout, 'buffer', sys.stdout))