17 files changed, 313 insertions, 34 deletions
diff --git a/Documentation/RelNotes/2.34.0.txt b/Documentation/RelNotes/2.34.0.txt
index d21a63ed83..7ce5ab7cc2 100644
--- a/Documentation/RelNotes/2.34.0.txt
+++ b/Documentation/RelNotes/2.34.0.txt
@@ -34,6 +34,20 @@ UI, Workflows & Features
    interactive when the help.autocorrect configuration variable is set
    to 'prompt'.
 
+ * "git maintenance" scheduler learned to use systemd timers as a
+   possible backend.
+
+ * "git diff --submodule=diff" showed failure from run_command() when
+   trying to run diff inside a submodule, when the user manually
+   removes the submodule directory.
+
+ * "git bundle unbundle" learned to show progress display.
+
+ * In cone mode, the sparse-index code path learned to remove ignored
+   files (like build artifacts) outside the sparse cone, allowing the
+   entire directory outside the sparse cone to be removed, which is
+   especially useful when the sparse patterns change.
+
 
 Performance, Internal Implementation, Development Support etc.
 
@@ -74,6 +88,37 @@ Performance, Internal Implementation, Development Support etc.
  * Callers from older advice_config[] based API has been updated to
    use the newer advice_if_enabled() and advice_enabled() API.
 
+ * Teach "test_pause" and "debug" helpers to allow using the HOME and
+   TERM environment variables the user usually uses.
+
+ * "make INSTALL_STRIP=-s install" allows the installation step to use
+   "install -s" to strip the binaries as they get installed.
+
+ * Code that handles large number of refs in the "git fetch" code
+   path has been optimized.
+
+ * The reachability bitmap file used to be generated only for a single
+   pack, but now we've learned to generate bitmaps for history that
+   span across multiple packfiles.
+
+ * The code to make "git grep" recurse into submodules has been
+   updated to migrate away from the "add submodule's object store as
+   an alternate object store" mechanism (which is suboptimal).
+
+ * The tracing of process ancestry information has been enhanced.
+
+ * Reduce number of write(2) system calls while sending the
+   ref advertisement.
+
+ * Update the build procedure to use the "-pedantic" build when
+   DEVELOPER makefile macro is in effect.
+
+ * Large part of "git submodule add" gets rewritten in C.
+
+ * The run-command API has been updated so that the callers can easily
+   ask the file descriptors open for packfiles to be closed immediately
+   before spawning commands that may trigger auto-gc.
+
 
 Fixes since v2.33
 -----------------
@@ -168,6 +213,38 @@ Fixes since v2.33
  * Doc update plus improved error reporting.
    (merge 1e93770888 jk/log-warn-on-bogus-encoding later to maint).
 
+ * Recent "diff -m" changes broke "gitk", which has been corrected.
+   (merge 5acffd3473 so/diff-index-regression-fix later to maint).
+
+ * Regression fix.
+   (merge b996f84989 ab/send-email-config-fix later to maint).
+
+ * The "git apply -3" code path learned not to bother the lower level
+   merge machinery when the three-way merge can be trivially resolved
+   without the content level merge.  This fixes a regression caused by
+   recent "-3way first and fall back to direct application" change.
+   (merge 57f183b698 jc/trivial-threeway-binary-merge later to maint).
+
+ * The code that optionally creates the *.rev reverse index file has
+   been optimized to avoid needless computation when it is not writing
+   the file out.
+   (merge 8fe8bae9d2 ab/reverse-midx-optim later to maint).
+
+ * "git range-diff -I... <range> <range>" segfaulted, which has been
+   corrected.
+   (merge 709b3f32d3 rs/range-diff-avoid-segfault-with-I later to maint).
+
+ * The order in which various files that make up a single (conceptual)
+   packfile has been reevaluated and straightened up.  This matters in
+   correctness, as an incomplete set of files must not be shown to a
+   running Git.
+   (merge 4bc1fd6e39 tb/pack-finalize-ordering later to maint).
+
+ * The "mode" word is useless in a call to open(2) that does not
+   create a new file.  Such a call in the files backend of the ref
+   subsystem has been cleaned up.
+   (merge 35cf94eaf6 rs/no-mode-to-open-when-appending later to maint).
+
  * Other code cleanup, docfix, build fix, etc.
    (merge 1d9c8daef8 ab/bundle-doc later to maint).
    (merge 81483fe613 en/merge-strategy-docs later to maint).
@@ -194,3 +271,8 @@ Fixes since v2.33
    (merge e4f8d27585 rs/show-branch-simplify later to maint).
    (merge e124ecf7f7 rs/archive-use-object-id later to maint).
    (merge cebead1ebf cb/ci-build-pedantic later to maint).
+   (merge ca0cc98e03 bs/doc-bugreport-outdir later to maint).
+   (merge 72b113e562 ab/no-more-check-bindir later to maint).
+   (merge 92a5d1c9b4 jc/prefix-filename-allocates later to maint).
+   (merge d9a65b6c0a rs/setup-use-xopen-and-xdup later to maint).
+   (merge e8f55568de jk/t5562-racefix later to maint).
diff --git a/Documentation/git-am.txt b/Documentation/git-am.txt
index 8714dfcb76..0a4a984dfd 100644
--- a/Documentation/git-am.txt
+++ b/Documentation/git-am.txt
@@ -178,6 +178,8 @@ default.   You can use `--no-utf8` to override this.
 
 --abort::
 	Restore the original branch and abort the patching operation.
+	Revert contents of files involved in the am operation to their
+	pre-am state.
 
 --quit::
 	Abort the patching operation but keep HEAD and the index
diff --git a/Documentation/git-bugreport.txt b/Documentation/git-bugreport.txt
index 66e88c2e31..d8817bf3ce 100644
--- a/Documentation/git-bugreport.txt
+++ b/Documentation/git-bugreport.txt
@@ -40,8 +40,8 @@ OPTIONS
 -------
 -o <path>::
 --output-directory <path>::
-	Place the resulting bug report file in `<path>` instead of the root of
-	the Git repository.
+	Place the resulting bug report file in `<path>` instead of the current
+	directory.
 
 -s <format>::
 --suffix <format>::
diff --git a/Documentation/git-bundle.txt b/Documentation/git-bundle.txt
index ac0d003835..71b5ecabd1 100644
--- a/Documentation/git-bundle.txt
+++ b/Documentation/git-bundle.txt
@@ -13,7 +13,7 @@ SYNOPSIS
 		    [--version=<version>] <file> <git-rev-list-args>
 'git bundle' verify [-q | --quiet] <file>
 'git bundle' list-heads <file> [<refname>...]
-'git bundle' unbundle <file> [<refname>...]
+'git bundle' unbundle [--progress] <file> [<refname>...]
 
 DESCRIPTION
 -----------
diff --git a/Documentation/git-config.txt b/Documentation/git-config.txt
index 2dc4bae6da..992225f612 100644
--- a/Documentation/git-config.txt
+++ b/Documentation/git-config.txt
@@ -71,6 +71,9 @@ codes are:
 
 On success, the command returns the exit code 0.
 
+A list of all available configuration variables can be obtained using the
+`git help --config` command.
+
 [[OPTIONS]]
 OPTIONS
 -------
diff --git a/Documentation/git-http-backend.txt b/Documentation/git-http-backend.txt
index 558966aa83..0c5c0dde19 100644
--- a/Documentation/git-http-backend.txt
+++ b/Documentation/git-http-backend.txt
@@ -16,7 +16,9 @@ A simple CGI program to serve the contents of a Git repository to Git
 clients accessing the repository over http:// and https:// protocols.
 The program supports clients fetching using both the smart HTTP protocol
 and the backwards-compatible dumb HTTP protocol, as well as clients
-pushing using the smart HTTP protocol.
+pushing using the smart HTTP protocol. It also supports Git's
+more-efficient "v2" protocol if properly configured; see the
+discussion of `GIT_PROTOCOL` in the ENVIRONMENT section below.
 
 It verifies that the directory has the magic file
 "git-daemon-export-ok", and it will refuse to export any Git directory
@@ -77,6 +79,18 @@ Apache 2.x::
 SetEnv GIT_PROJECT_ROOT /var/www/git
 SetEnv GIT_HTTP_EXPORT_ALL
 ScriptAlias /git/ /usr/libexec/git-core/git-http-backend/
+
+# This is not strictly necessary using Apache and a modern version of
+# git-http-backend, as the webserver will pass along the header in the
+# environment as HTTP_GIT_PROTOCOL, and http-backend will copy that into
+# GIT_PROTOCOL. But you may need this line (or something similar if you
+# are using a different webserver), or if you want to support older Git
+# versions that did not do that copying.
+#
+# Having the webserver set up GIT_PROTOCOL is perfectly fine even with
+# modern versions (and will take precedence over HTTP_GIT_PROTOCOL,
+# which means it can be used to override the client's request).
+SetEnvIf Git-Protocol ".*" GIT_PROTOCOL=$0
 ----------------------------------------------------------------
 +
 To enable anonymous read access but authenticated write access,
@@ -264,6 +278,16 @@ a repository with an extremely large number of refs.  The value can be
 specified with a unit (e.g., `100M` for 100 megabytes). The default is
 10 megabytes.
 
+Clients may probe for optional protocol capabilities (like the v2
+protocol) using the `Git-Protocol` HTTP header. In order to support
+these, the contents of that header must appear in the `GIT_PROTOCOL`
+environment variable. Most webservers will pass this header to the CGI
+via the `HTTP_GIT_PROTOCOL` variable, and `git-http-backend` will
+automatically copy that to `GIT_PROTOCOL`. However, some webservers may
+be more selective about which headers they'll pass, in which case they
+need to be configured explicitly (see the mention of `Git-Protocol` in
+the Apache config from the earlier EXAMPLES section).
+
 The backend process sets GIT_COMMITTER_NAME to '$REMOTE_USER' and
 GIT_COMMITTER_EMAIL to '$\{REMOTE_USER}@http.$\{REMOTE_ADDR\}',
 ensuring that any reflogs created by 'git-receive-pack' contain some
diff --git a/Documentation/git-index-pack.txt b/Documentation/git-index-pack.txt
index 7fa74b9e79..1f1e359225 100644
--- a/Documentation/git-index-pack.txt
+++ b/Documentation/git-index-pack.txt
@@ -82,6 +82,12 @@ OPTIONS
 --strict::
 	Die, if the pack contains broken objects or links.
 
+--progress-title::
+	For internal use only.
++
+Set the title of the progress bar. The title is "Receiving objects" by
+default and "Indexing objects" when `--stdin` is specified.
+
 --check-self-contained-and-connected::
 	Die if the pack contains broken links. For internal use only.
 
diff --git a/Documentation/git-maintenance.txt b/Documentation/git-maintenance.txt
index 1e738ad398..e2cfb68ab5 100644
--- a/Documentation/git-maintenance.txt
+++ b/Documentation/git-maintenance.txt
@@ -179,6 +179,17 @@ OPTIONS
 	`maintenance.<task>.enabled` configured as `true` are considered.
 	See the 'TASKS' section for the list of accepted `<task>` values.
 
+--scheduler=auto|crontab|systemd-timer|launchctl|schtasks::
+	When combined with the `start` subcommand, specify the scheduler
+	for running the hourly, daily and weekly executions of
+	`git maintenance run`.
+	Possible values for `<scheduler>` are `auto`, `crontab`
+	(POSIX), `systemd-timer` (Linux), `launchctl` (macOS), and
+	`schtasks` (Windows). When `auto` is specified, the
+	appropriate platform-specific scheduler is used; on Linux,
+	`systemd-timer` is used if available, otherwise
+	`crontab`. Default is `auto`.
+
 
 TROUBLESHOOTING
 ---------------
@@ -277,6 +288,52 @@ schedule to ensure you are executing the correct binaries in your
 schedule.
 
 
+BACKGROUND MAINTENANCE ON LINUX SYSTEMD SYSTEMS
+-----------------------------------------------
+
+While Linux supports `cron`, depending on the distribution, `cron` may
+be an optional package not necessarily installed. On modern Linux
+distributions, systemd timers are superseding it.
+
+If user systemd timers are available, they will be used as a replacement
+of `cron`.
+
+In this case, `git maintenance start` will create user systemd timer units
+and start the timers. The current list of user-scheduled tasks can be found
+by running `systemctl --user list-timers`. The timers written by `git
+maintenance start` are similar to this:
+
+-----------------------------------------------------------------------
+$ systemctl --user list-timers
+NEXT                         LEFT          LAST                         PASSED     UNIT                         ACTIVATES
+Thu 2021-04-29 19:00:00 CEST 42min left    Thu 2021-04-29 18:00:11 CEST 17min ago  git-maintenance@hourly.timer git-maintenance@hourly.service
+Fri 2021-04-30 00:00:00 CEST 5h 42min left Thu 2021-04-29 00:00:11 CEST 18h ago    git-maintenance@daily.timer  git-maintenance@daily.service
+Mon 2021-05-03 00:00:00 CEST 3 days left   Mon 2021-04-26 00:00:11 CEST 3 days ago git-maintenance@weekly.timer git-maintenance@weekly.service
+-----------------------------------------------------------------------
+
+One timer is registered for each `--schedule=<frequency>` option.
+
+The definition of the systemd units can be inspected in the following files:
+
+-----------------------------------------------------------------------
+~/.config/systemd/user/git-maintenance@.timer
+~/.config/systemd/user/git-maintenance@.service
+~/.config/systemd/user/timers.target.wants/git-maintenance@hourly.timer
+~/.config/systemd/user/timers.target.wants/git-maintenance@daily.timer
+~/.config/systemd/user/timers.target.wants/git-maintenance@weekly.timer
+-----------------------------------------------------------------------
+
+`git maintenance start` will overwrite these files and start the timer
+again with `systemctl --user`, so any customization should be done by
+creating a drop-in file, i.e. a `.conf` suffixed file in the
+`~/.config/systemd/user/git-maintenance@.service.d` directory.
+
+`git maintenance stop` will stop the user systemd timers and delete
+the above mentioned files.
+
+For more details, see `systemd.timer(5)`.
+
+
 BACKGROUND MAINTENANCE ON MACOS SYSTEMS
 ---------------------------------------
 
diff --git a/Documentation/git-multi-pack-index.txt b/Documentation/git-multi-pack-index.txt
index ffd601bc17..a9df3dbd32 100644
--- a/Documentation/git-multi-pack-index.txt
+++ b/Documentation/git-multi-pack-index.txt
@@ -10,7 +10,7 @@ SYNOPSIS
 --------
 [verse]
 'git multi-pack-index' [--object-dir=<dir>] [--[no-]progress]
-	[--preferred-pack=<pack>] <subcommand>
+	[--preferred-pack=<pack>] [--[no-]bitmap] <subcommand>
 
 DESCRIPTION
 -----------
@@ -23,6 +23,8 @@ OPTIONS
 	Use given directory for the location of Git objects. We check
 	`<dir>/packs/multi-pack-index` for the current MIDX file, and
 	`<dir>/packs` for the pack-files to index.
++
+`<dir>` must be an alternate of the current repository.
 
 --[no-]progress::
 	Turn progress on/off explicitly. If neither is specified, progress is
@@ -37,9 +39,12 @@ write::
 --
 	--preferred-pack=<pack>::
 		Optionally specify the tie-breaking pack used when
-		multiple packs contain the same object. If not given,
-		ties are broken in favor of the pack with the lowest
-		mtime.
+		multiple packs contain the same object. `<pack>` must
+		contain at least one object. If not given, ties are
+		broken in favor of the pack with the lowest mtime.
+
+	--[no-]bitmap::
+		Control whether or not a multi-pack bitmap is written.
 --
 
 verify::
@@ -81,6 +86,13 @@ EXAMPLES
 $ git multi-pack-index write
 -----------------------------------------------
 
+* Write a MIDX file for the packfiles in the current .git folder with a
+corresponding bitmap.
++
+-------------------------------------------------------------
+$ git multi-pack-index write --preferred-pack=<pack> --bitmap
+-------------------------------------------------------------
+
 * Write a MIDX file for the packfiles in an alternate object store.
 +
 -----------------------------------------------
diff --git a/Documentation/git-receive-pack.txt b/Documentation/git-receive-pack.txt
index 25702ed730..014a78409b 100644
--- a/Documentation/git-receive-pack.txt
+++ b/Documentation/git-receive-pack.txt
@@ -41,6 +41,11 @@ OPTIONS
 <directory>::
 	The repository to sync into.
 
+--http-backend-info-refs::
+	Used by linkgit:git-http-backend[1] to serve up
+	`$GIT_URL/info/refs?service=git-receive-pack` requests. See
+	`--http-backend-info-refs` in linkgit:git-upload-pack[1].
+
 PRE-RECEIVE HOOK
 ----------------
 Before any ref is updated, if $GIT_DIR/hooks/pre-receive file exists
diff --git a/Documentation/git-sparse-checkout.txt b/Documentation/git-sparse-checkout.txt
index fdcf43f87c..42056ee9ff 100644
--- a/Documentation/git-sparse-checkout.txt
+++ b/Documentation/git-sparse-checkout.txt
@@ -210,6 +210,16 @@ case-insensitive check. This corrects for case mismatched filenames in the
 'git sparse-checkout set' command to reflect the expected cone in the working
 directory.
 
+When changing the sparse-checkout patterns in cone mode, Git will inspect each
+tracked directory that is not within the sparse-checkout cone to see if it
+contains any untracked files. If all of those files are ignored due to the
+`.gitignore` patterns, then the directory will be deleted. If any of the
+untracked files within that directory is not ignored, then no deletions will
+occur within that directory and a warning message will appear. If these files
+are important, then reset your sparse-checkout definition so they are included,
+use `git add` and `git commit` to store them, then remove any remaining files
+manually to ensure Git can behave optimally.
+
 
 SUBMODULES
 ----------
diff --git a/Documentation/git-upload-pack.txt b/Documentation/git-upload-pack.txt
index 9822c1eb1a..8f87b23ea8 100644
--- a/Documentation/git-upload-pack.txt
+++ b/Documentation/git-upload-pack.txt
@@ -36,14 +36,26 @@ OPTIONS
 	This fits with the HTTP POST request processing model where
 	a program may read the request, write a response, and must exit.
 
---advertise-refs::
-	Only the initial ref advertisement is output, and the program exits
-	immediately. This fits with the HTTP GET request model, where
-	no request content is received but a response must be produced.
+--http-backend-info-refs::
+	Used by linkgit:git-http-backend[1] to serve up
+	`$GIT_URL/info/refs?service=git-upload-pack` requests. See
+	"Smart Clients" in link:technical/http-protocol.html[the HTTP
+	transfer protocols] documentation and "HTTP Transport" in
+	link:technical/protocol-v2.html[the Git Wire Protocol, Version
+	2] documentation. Also understood by
+	linkgit:git-receive-pack[1].
 
 <directory>::
 	The repository to sync from.
 
+ENVIRONMENT
+-----------
+
+`GIT_PROTOCOL`::
+	Internal variable used for handshaking the wire protocol. Server
+	admins may need to configure some transports to allow this
+	variable to be passed. See the discussion in linkgit:git[1].
+
 SEE ALSO
 --------
 linkgit:gitnamespaces[7]
diff --git a/Documentation/git.txt b/Documentation/git.txt
index 6dd241ef83..e4b82599fc 100644
--- a/Documentation/git.txt
+++ b/Documentation/git.txt
@@ -894,6 +894,21 @@ for full details.
 	Contains a colon ':' separated list of keys with optional values
 	'key[=value]'.  Presence of unknown keys and values must be
 	ignored.
++
+Note that servers may need to be configured to allow this variable to
+pass over some transports. It will be propagated automatically when
+accessing local repositories (i.e., `file://` or a filesystem path), as
+well as over the `git://` protocol. For git-over-http, it should work
+automatically in most configurations, but see the discussion in
+linkgit:git-http-backend[1]. For git-over-ssh, the ssh server may need
+to be configured to allow clients to pass this variable (e.g., by using
+`AcceptEnv GIT_PROTOCOL` with OpenSSH).
++
+This configuration is optional. If the variable is not propagated, then
+clients will fall back to the original "v0" protocol (but may miss out
+on some performance improvements or features). This variable currently
+only affects clones and fetches; it is not yet used for pushes (but may
+be in the future).
 
 `GIT_OPTIONAL_LOCKS`::
 	If set to `0`, Git will complete any requested operation without
diff --git a/Documentation/technical/bitmap-format.txt b/Documentation/technical/bitmap-format.txt
index f8c18a0f7a..04b3ec2178 100644
--- a/Documentation/technical/bitmap-format.txt
+++ b/Documentation/technical/bitmap-format.txt
@@ -1,6 +1,44 @@
 GIT bitmap v1 format
 ====================
 
+== Pack and multi-pack bitmaps
+
+Bitmaps store reachability information about the set of objects in a packfile,
+or a multi-pack index (MIDX). The former is defined obviously, and the latter is
+defined as the union of objects in packs contained in the MIDX.
+
+A bitmap may belong to either one pack, or the repository's multi-pack index (if
+it exists). A repository may have at most one bitmap.
+
+An object is uniquely described by its bit position within a bitmap:
+
+	- If the bitmap belongs to a packfile, the __n__th bit corresponds to
+	the __n__th object in pack order. For a function `offset` which maps
+	objects to their byte offset within a pack, pack order is defined as
+	follows:
+
+		o1 <= o2 <==> offset(o1) <= offset(o2)
+
+	- If the bitmap belongs to a MIDX, the __n__th bit corresponds to the
+	__n__th object in MIDX order. With an additional function `pack` which
+	maps objects to the pack they were selected from by the MIDX, MIDX order
+	is defined as follows:
+
+		o1 <= o2 <==> pack(o1) <= pack(o2) /\ offset(o1) <= offset(o2)
+
+	The ordering between packs is done according to the MIDX's .rev file.
+	Notably, the preferred pack sorts ahead of all other packs.
+
+The on-disk representation (described below) of a bitmap is the same regardless
+of whether or not that bitmap belongs to a packfile or a MIDX. The only
+difference is the interpretation of the bits, which is described above.
+
+Certain bitmap extensions are supported (see: Appendix B). No extensions are
+required for bitmaps corresponding to packfiles. For bitmaps that correspond to
+MIDXs, both the bit-cache and rev-cache extensions are required.
+
+== On-disk format
+
 	- A header appears at the beginning:
 
 		4-byte signature: {'B', 'I', 'T', 'M'}
@@ -14,17 +52,19 @@ GIT bitmap v1 format
 			The following flags are supported:
 
 			- BITMAP_OPT_FULL_DAG (0x1) REQUIRED
-			This flag must always be present. It implies that the bitmap
-			index has been generated for a packfile with full closure
-			(i.e. where every single object in the packfile can find
-			 its parent links inside the same packfile). This is a
-			requirement for the bitmap index format, also present in JGit,
-			that greatly reduces the complexity of the implementation.
+			This flag must always be present. It implies that the
+			bitmap index has been generated for a packfile or
+			multi-pack index (MIDX) with full closure (i.e. where
+			every single object in the packfile/MIDX can find its
+			parent links inside the same packfile/MIDX). This is a
+			requirement for the bitmap index format, also present in
+			JGit, that greatly reduces the complexity of the
+			implementation.
 
 			- BITMAP_OPT_HASH_CACHE (0x4)
 			If present, the end of the bitmap file contains
 			`N` 32-bit name-hash values, one per object in the
-			pack. The format and meaning of the name-hash is
+			pack/MIDX. The format and meaning of the name-hash is
 			described below.
 
 		4-byte entry count (network byte order)
@@ -33,7 +73,8 @@ GIT bitmap v1 format
 
 		20-byte checksum
 
-			The SHA1 checksum of the pack this bitmap index belongs to.
+			The SHA1 checksum of the pack/MIDX this bitmap index
+			belongs to.
 
 	- 4 EWAH bitmaps that act as type indexes
 
@@ -50,7 +91,7 @@ GIT bitmap v1 format
 			- Tags
 
 		In each bitmap, the `n`th bit is set to true if the `n`th object
-		in the packfile is of that type.
+		in the packfile or multi-pack index is of that type.
 
 		The obvious consequence is that the OR of all 4 bitmaps will result
 		in a full set (all bits set), and the AND of all 4 bitmaps will
@@ -62,8 +103,9 @@ GIT bitmap v1 format
 		Each entry contains the following:
 
 		- 4-byte object position (network byte order)
-			The position **in the index for the packfile** where the
-			bitmap for this commit is found.
+			The position **in the index for the packfile or
+			multi-pack index** where the bitmap for this commit is
+			found.
 
 		- 1-byte XOR-offset
 			The xor offset used to compress this bitmap. For an entry
@@ -146,10 +188,11 @@ Name-hash cache
 ---------------
 
 If the BITMAP_OPT_HASH_CACHE flag is set, the end of the bitmap contains
-a cache of 32-bit values, one per object in the pack. The value at
+a cache of 32-bit values, one per object in the pack/MIDX. The value at
 position `i` is the hash of the pathname at which the `i`th object
-(counting in index order) in the pack can be found.  This can be fed
-into the delta heuristics to compare objects with similar pathnames.
+(counting in index or multi-pack index order) in the pack/MIDX can be found.
+This can be fed into the delta heuristics to compare objects with similar
+pathnames.
 
 The hash algorithm used is:
 
diff --git a/Documentation/technical/http-protocol.txt b/Documentation/technical/http-protocol.txt
index 96d89ea9b2..cc5126cfed 100644
--- a/Documentation/technical/http-protocol.txt
+++ b/Documentation/technical/http-protocol.txt
@@ -225,6 +225,9 @@ The client may send Extra Parameters (see
 Documentation/technical/pack-protocol.txt) as a colon-separated string
 in the Git-Protocol HTTP header.
 
+Uses the `--http-backend-info-refs` option to
+linkgit:git-upload-pack[1].
+
 Dumb Server Response
 ^^^^^^^^^^^^^^^^^^^^
 Dumb servers MUST respond with the dumb server reply format.
diff --git a/Documentation/technical/multi-pack-index.txt b/Documentation/technical/multi-pack-index.txt
index fb688976c4..1a73c3ee20 100644
--- a/Documentation/technical/multi-pack-index.txt
+++ b/Documentation/technical/multi-pack-index.txt
@@ -71,14 +71,10 @@ Future Work
   still reducing the number of binary searches required for object
   lookups.
 
-- The reachability bitmap is currently paired directly with a single
-  packfile, using the pack-order as the object order to hopefully
-  compress the bitmaps well using run-length encoding. This could be
-  extended to pair a reachability bitmap with a multi-pack-index. If
-  the multi-pack-index is extended to store a "stable object order"
+- If the multi-pack-index is extended to store a "stable object order"
   (a function Order(hash) = integer that is constant for a given hash,
-  even as the multi-pack-index is updated) then a reachability bitmap
-  could point to a multi-pack-index and be updated independently.
+  even as the multi-pack-index is updated) then MIDX bitmaps could be
+  updated independently of the MIDX.
 
 - Packfiles can be marked as "special" using empty files that share
   the initial name but replace ".pack" with ".keep" or ".promisor".
diff --git a/Documentation/technical/protocol-v2.txt b/Documentation/technical/protocol-v2.txt
index 1040d85319..59b86fcf97 100644
--- a/Documentation/technical/protocol-v2.txt
+++ b/Documentation/technical/protocol-v2.txt
@@ -42,7 +42,8 @@ Initial Client Request
 In general a client can request to speak protocol v2 by sending
 `version=2` through the respective side-channel for the transport being
 used which inevitably sets `GIT_PROTOCOL`.  More information can be
-found in `pack-protocol.txt` and `http-protocol.txt`.  In all cases the
+found in `pack-protocol.txt` and `http-protocol.txt`, as well as the
+`GIT_PROTOCOL` definition in `git.txt`. In all cases the
 response from the server is the capability advertisement.
 
 Git Transport
@@ -58,6 +59,8 @@ SSH and File Transport
 
 When using either the ssh:// or file:// transport, the GIT_PROTOCOL
 environment variable must be set explicitly to include "version=2".
+The server may need to be configured to allow this environment variable
+to pass.
 
 HTTP Transport
 ~~~~~~~~~~~~~~
@@ -81,6 +84,12 @@ A v2 server would reply:
 Subsequent requests are then made directly to the service
 `$GIT_URL/git-upload-pack`. (This works the same for git-receive-pack).
 
+Uses the `--http-backend-info-refs` option to
+linkgit:git-upload-pack[1].
+
+The server may need to be configured to pass this header's contents via
+the `GIT_PROTOCOL` variable. See the discussion in `git-http-backend.txt`.
+
 Capability Advertisement
 ------------------------