fsmonitor: teach git to optionally utilize a file system monitor to speed up detecting new or changed files.

When the index is read from disk, the fsmonitor index extension is used
to flag the last known potentially dirty index entries. The registered
core.fsmonitor command is called with the time the index was last
updated and returns the list of files changed since that time. This list
is used to flag any additional dirty cache entries and untracked cache
directories.

We can then use this valid state to speed up preload_index(),
ie_match_stat(), and refresh_cache_ent() as they do not need to lstat()
files to detect potential changes for those entries marked
CE_FSMONITOR_VALID.

In addition, if the untracked cache is turned on valid_cached_dir() can
skip checking directories for new or changed files as fsmonitor will
invalidate the cache only for those directories that have been
identified as having potential changes.

To keep the CE_FSMONITOR_VALID state accurate during git operations;
when git updates a cache entry to match the current state on disk,
it will now set the CE_FSMONITOR_VALID bit.

Inversely, anytime git changes a cache entry, the CE_FSMONITOR_VALID bit
is cleared and the corresponding untracked cache directory is marked
invalid.

Signed-off-by: Ben Peart <benpeart@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 66 insertions, 0 deletions

diff --git a/fsmonitor.h b/fsmonitor.h
new file mode 100644
index 0000000..0de644e
--- /dev/null
+++ b/fsmonitor.h
@@ -0,0 +1,66 @@
+#ifndef FSMONITOR_H
+#define FSMONITOR_H
+
+extern struct trace_key trace_fsmonitor;
+
+/*
+ * Read the fsmonitor index extension and (if configured) restore the
+ * CE_FSMONITOR_VALID state.
+ */
+extern int read_fsmonitor_extension(struct index_state *istate, const void *data, unsigned long sz);
+
+/*
+ * Write the CE_FSMONITOR_VALID state into the fsmonitor index extension.
+ */
+extern void write_fsmonitor_extension(struct strbuf *sb, struct index_state *istate);
+
+/*
+ * Add/remove the fsmonitor index extension
+ */
+extern void add_fsmonitor(struct index_state *istate);
+extern void remove_fsmonitor(struct index_state *istate);
+
+/*
+ * Add/remove the fsmonitor index extension as necessary based on the current
+ * core.fsmonitor setting.
+ */
+extern void tweak_fsmonitor(struct index_state *istate);
+
+/*
+ * Run the configured fsmonitor integration script and clear the
+ * CE_FSMONITOR_VALID bit for any files returned as dirty.  Also invalidate
+ * any corresponding untracked cache directory structures. Optimized to only
+ * run the first time it is called.
+ */
+extern void refresh_fsmonitor(struct index_state *istate);
+
+/*
+ * Set the given cache entries CE_FSMONITOR_VALID bit. This should be
+ * called any time the cache entry has been updated to reflect the
+ * current state of the file on disk.
+ */
+static inline void mark_fsmonitor_valid(struct cache_entry *ce)
+{
+	if (core_fsmonitor) {
+		ce->ce_flags |= CE_FSMONITOR_VALID;
+		trace_printf_key(&trace_fsmonitor, "mark_fsmonitor_clean '%s'", ce->name);
+	}
+}
+
+/*
+ * Clear the given cache entry's CE_FSMONITOR_VALID bit and invalidate
+ * any corresponding untracked cache directory structures. This should
+ * be called any time git creates or modifies a file that should
+ * trigger an lstat() or invalidate the untracked cache for the
+ * corresponding directory
+ */
+static inline void mark_fsmonitor_invalid(struct index_state *istate, struct cache_entry *ce)
+{
+	if (core_fsmonitor) {
+		ce->ce_flags &= ~CE_FSMONITOR_VALID;
+		untracked_cache_invalidate_path(istate, ce->name);
+		trace_printf_key(&trace_fsmonitor, "mark_fsmonitor_invalid '%s'", ce->name);
+	}
+}
+
+#endif