[PATCH v5 5/7] fsmonitor: add documentation for the fsmonitor extension.

[Ben Peart <peartben@gmail.com>]

This includes the core.fsmonitor setting, the query-fsmonitor hook,
and the fsmonitor index extension.

Signed-off-by: Ben Peart <benpeart@microsoft.com>
---
 Documentation/config.txt                 |  7 +++++++
 Documentation/githooks.txt               | 23 +++++++++++++++++++++++
 Documentation/technical/index-format.txt | 19 +++++++++++++++++++
 3 files changed, 49 insertions(+)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index dd4beec39d..d883e3318c 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -410,6 +410,13 @@ core.protectNTFS::
 	8.3 "short" names.
 	Defaults to `true` on Windows, and `false` elsewhere.
 
+core.fsmonitor::
+	If set to true, call the query-fsmonitor hook proc which will
+	identify all files that may have had changes since the last
+	request. This information is used to speed up operations like
+	'git commit' and 'git status' by limiting what git must scan to
+	detect changes.
+
 core.trustctime::
 	If false, the ctime differences between the index and the
 	working tree are ignored; useful when the inode change time
diff --git a/Documentation/githooks.txt b/Documentation/githooks.txt
index b2514f4d44..219786b2da 100644
--- a/Documentation/githooks.txt
+++ b/Documentation/githooks.txt
@@ -456,6 +456,29 @@ non-zero status causes 'git send-email' to abort before sending any
 e-mails.
 
 
+[[query-fsmonitor]]
+query-fsmonitor
+~~~~~~~~~~~~~~~
+
+This hook is invoked when the configuration option core.fsmonitor is
+set and git needs to identify changed or untracked files.  It takes
+two arguments, a version (currently 1) and the time in elapsed
+nanoseconds since midnight, January 1, 1970.
+
+The hook should output to stdout the list of all files in the working
+directory that may have changed since the requested time.  The logic
+should be inclusive so that it does not miss any potential changes.
+The paths should be relative to the root of the working directory
+and be separated by a single NUL.
+
+Git will limit what files it checks for changes as well as which
+directories are checked for untracked files based on the path names
+given.
+
+The exit status determines whether git will use the data from the
+hook to limit its search.  On error, it will fall back to verifying
+all files and folders.
+
 GIT
 ---
 Part of the linkgit:git[1] suite
diff --git a/Documentation/technical/index-format.txt b/Documentation/technical/index-format.txt
index ade0b0c445..7aeeea6f94 100644
--- a/Documentation/technical/index-format.txt
+++ b/Documentation/technical/index-format.txt
@@ -295,3 +295,22 @@ The remaining data of each directory block is grouped by type:
     in the previous ewah bitmap.
 
   - One NUL.
+
+== File System Monitor cache
+
+  The file system monitor cache tracks files for which the query-fsmonitor
+  hook has told us about changes.  The signature for this extension is
+  { 'F', 'S', 'M', 'N' }.
+
+  The extension starts with
+
+  - 32-bit version number: the current supported version is 1.
+
+  - 64-bit time: the extension data reflects all changes through the given
+	time which is stored as the nanoseconds elapsed since midnight,
+	January 1, 1970.
+
+  - 32-bit bitmap size: the size of the CE_FSMONITOR_DIRTY bitmap.
+
+  - An ewah bitmap, the n-th bit indicates whether the n-th index entry
+    is CE_FSMONITOR_DIRTY.
-- 
2.13.0