annotate mercurial/help/diffs.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
author Gregory Szorc <gregory.szorc@gmail.com>
date Tue, 13 Nov 2018 12:30:59 -0800
parents ebfc46929f3e
children
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1 Mercurial's default format for showing changes between two versions of
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2 a file is compatible with the unified format of GNU diff, which can be
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3 used by GNU patch and many other standard tools.
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5 While this standard format is often enough, it does not encode the
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6 following information:
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8 - executable status and other permission bits
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9 - copy or rename information
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10 - changes in binary files
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11 - creation or deletion of empty files
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13 Mercurial also supports the extended diff format from the git VCS
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14 which addresses these limitations. The git diff format is not produced
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15 by default because a few widespread tools still do not understand this
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16 format.
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18 This means that when generating diffs from a Mercurial repository
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19 (e.g. with :hg:`export`), you should be careful about things like file
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20 copies and renames or other things mentioned above, because when
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21 applying a standard diff to a different repository, this extra
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22 information is lost. Mercurial's internal operations (like push and
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23 pull) are not affected by this, because they use an internal binary
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24 format for communicating changes.
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26 To make Mercurial produce the git extended diff format, use the --git
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27 option available for many commands, or set 'git = True' in the [diff]
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28 section of your configuration file. You do not need to set this option
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29 when importing diffs in this format or using them in the mq extension.