view mercurial/help/hg.1.txt @ 40626:87a872555e90

revlog: detect incomplete revlog reads

_readsegment() is supposed to return N bytes of revlog revision
data starting at a file offset. Surprisingly, its behavior before
this patch never verified that it actually read and returned N
bytes! Instead, it would perform the read(), then return whatever
data was available. And even more surprisingly, nothing in the
call chain appears to have been validating that it received all
the data it was expecting.

This behavior could lead to partial or incomplete revision chunks
being operated on. This could result in e.g. cached deltas being
applied against incomplete base revisions. The delta application
process would happily perform this operation. Only hash
verification would detect the corruption and save us.

This commit changes the behavior of raw revlog reading to validate
that we actually read() the number of bytes that were requested.
We will raise a more specific error faster, rather than possibly
have it go undetected or manifest later in the call stack, at
delta application or hash verification.

Differential Revision: https://phab.mercurial-scm.org/D5266

====
 hg
====

---------------------------------------
Mercurial source code management system
---------------------------------------

:Author:         Matt Mackall <[e-mail]>
:Organization:   Mercurial
:Manual section: 1
:Manual group:   Mercurial Manual

.. contents::
   :backlinks: top
   :class: htmlonly
   :depth: 1


Synopsis
""""""""
**hg** *command* [*option*]... [*argument*]...

Description
"""""""""""
The **hg** command provides a command line interface to the Mercurial
system.

Command Elements
""""""""""""""""

files...
    indicates one or more filename or relative path filenames; see
    `File Name Patterns`_ for information on pattern matching

path
    indicates a path on the local machine

revision
    indicates a changeset which can be specified as a changeset
    revision number, a tag, or a unique substring of the changeset
    hash value

repository path
    either the pathname of a local repository or the URI of a remote
    repository.

.. include:: hg.1.gendoc.txt

Files
"""""

``/etc/mercurial/hgrc``, ``$HOME/.hgrc``, ``.hg/hgrc``
    This file contains defaults and configuration. Values in
    ``.hg/hgrc`` override those in ``$HOME/.hgrc``, and these override
    settings made in the global ``/etc/mercurial/hgrc`` configuration.
    See |hgrc(5)|_ for details of the contents and format of these
    files.

``.hgignore``
    This file contains regular expressions (one per line) that
    describe file names that should be ignored by **hg**. For details,
    see |hgignore(5)|_.

``.hgsub``
    This file defines the locations of all subrepositories, and
    tells where the subrepository checkouts came from. For details, see
    :hg:`help subrepos`.

``.hgsubstate``
    This file is where Mercurial stores all nested repository states. *NB: This
    file should not be edited manually.*

``.hgtags``
    This file contains changeset hash values and text tag names (one
    of each separated by spaces) that correspond to tagged versions of
    the repository contents. The file content is encoded using UTF-8.

``.hg/last-message.txt``
    This file is used by :hg:`commit` to store a backup of the commit message
    in case the commit fails.

``.hg/localtags``
    This file can be used to define local tags which are not shared among
    repositories. The file format is the same as for ``.hgtags``, but it is
    encoded using the local system encoding.

Some commands (e.g. revert) produce backup files ending in ``.orig``,
if the ``.orig`` file already exists and is not tracked by Mercurial,
it will be overwritten.

Bugs
""""
Probably lots, please post them to the mailing list (see Resources_
below) when you find them.

See Also
""""""""
|hgignore(5)|_, |hgrc(5)|_

Author
""""""
Written by Matt Mackall <[e-mail]>

Resources
"""""""""
Main Web Site: https://mercurial-scm.org/

Source code repository: https://www.mercurial-scm.org/repo/hg

Mailing list: https://www.mercurial-scm.org/mailman/listinfo/mercurial/

Copying
"""""""
Copyright (C) 2005-2018 Matt Mackall.
Free use of this software is granted under the terms of the GNU General
Public License version 2 or any later version.

.. include:: common.txt