1. 03 Jan, 2018 1 commit
    • diff_generate: avoid excessive stats of .gitattribute files · d8896bda
      When generating a diff between two trees, for each file that is to be
      diffed we have to determine whether it shall be treated as text or as
      binary files. While git has heuristics to determine which kind of diff
      to generate, users can also that default behaviour by setting or
      unsetting the 'diff' attribute for specific files.
      
      Because of that, we have to query gitattributes in order to determine
      how to diff the current files. Instead of hitting the '.gitattributes'
      file every time we need to query an attribute, which can get expensive
      especially on networked file systems, we try to cache them instead. This
      works perfectly fine for every '.gitattributes' file that is found, but
      we hit cache invalidation problems when we determine that an attribuse
      file is _not_ existing. We do create an entry in the cache for missing
      '.gitattributes' files, but as soon as we hit that file again we
      invalidate it and stat it again to see if it has now appeared.
      
      In the case of diffing large trees with each other, this behaviour is
      very suboptimal. For each pair of files that is to be diffed, we will
      repeatedly query every directory component leading towards their
      respective location for an attributes file. This leads to thousands or
      even hundreds of thousands of wasted syscalls.
      
      The attributes cache already has a mechanism to help in that scenario in
      form of the `git_attr_session`. As long as the same attributes session
      is still active, we will not try to re-query the gitmodules files at all
      but simply retain our currently cached results. To fix our problem, we
      can create a session at the top-most level, which is the initialization
      of the `git_diff` structure, and use it in order to look up the correct
      diff driver. As the `git_diff` structure is used to generate patches for
      multiple files at once, this neatly solves our problem by retaining the
      session until patches for all files have been generated.
      
      The fix has been tested with linux.git by calling
      `git_diff_tree_to_tree` and `git_diff_to_buf` with v4.10^{tree} and
      v4.14^{tree}.
      
                      | time    | .gitattributes stats
          without fix | 33.201s | 844614
          with fix    | 30.327s | 4441
      
      While execution only improved by roughly 10%, the stat(3) syscalls for
      .gitattributes files decreased by 99.5%. The benchmarks were quite
      simple with best-of-three timings on Linux ext4 systems. One can assume
      that for network based file systems the performance gain will be a lot
      larger due to a much higher latency.
      Patrick Steinhardt committed
  2. 03 Jul, 2017 1 commit
    • Make sure to always include "common.h" first · 0c7f49dd
      Next to including several files, our "common.h" header also declares
      various macros which are then used throughout the project. As such, we
      have to make sure to always include this file first in all
      implementation files. Otherwise, we might encounter problems or even
      silent behavioural differences due to macros or defines not being
      defined as they should be. So in fact, our header and implementation
      files should make sure to always include "common.h" first.
      
      This commit does so by establishing a common include pattern. Header
      files inside of "src" will now always include "common.h" as its first
      other file, separated by a newline from all the other includes to make
      it stand out as special. There are two cases for the implementation
      files. If they do have a matching header file, they will always include
      this one first, leading to "common.h" being transitively included as
      first file. If they do not have a matching header file, they instead
      include "common.h" as first file themselves.
      
      This fixes the outlined problems and will become our standard practice
      for header and source files inside of the "src/" from now on.
      Patrick Steinhardt committed
  3. 24 Jan, 2014 1 commit
    • Initial take on builtin drivers with multiline · a5a38643
      This extends the diff driver parser to support multiline driver
      definitions along with ! prefixing for negated matches.  This
      brings the driver function pattern parsing in line with core Git.
      
      This also adds an internal table of driver definitions and a
      fallback code path that will look in that table for diff drivers
      that are set with attributes without having a definition in the
      config file.  Right now, I just populated the table with a kind
      of simple HTML definition that is similar to the core Git def.
      Russell Belfer committed
  4. 12 Jun, 2013 1 commit
  5. 11 Jun, 2013 1 commit
    • Implement regex pattern diff driver · 5dc98298
      This implements the loading of regular expression pattern lists
      for diff drivers that search for function context in that way.
      This also changes the way that diff drivers update options and
      interface with xdiff APIs to make them a little more flexible.
      Russell Belfer committed
  6. 10 Jun, 2013 2 commits
    • Reorganize diff and add basic diff driver · 114f5a6c
      This is a significant reorganization of the diff code to break it
      into a set of more clearly distinct files and to document the new
      organization.  Hopefully this will make the diff code easier to
      understand and to extend.
      
      This adds a new `git_diff_driver` object that looks of diff driver
      information from the attributes and the config so that things like
      function content in diff headers can be provided.  The full driver
      spec is not implemented in the commit - this is focused on the
      reorganization of the code and putting the driver hooks in place.
      
      This also removes a few #includes from src/repository.h that were
      overbroad, but as a result required extra #includes in a variety
      of places since including src/repository.h no longer results in
      pulling in the whole world.
      Russell Belfer committed