fsmonitor: store fsmonitor bitmap before splitting index

ba1b9cac ("fsmonitor: delay updating state until after split index
is merged", 2017-10-27) resolved the problem of the fsmonitor data
being applied to the non-base index when reading; however, a similar
problem exists when writing the index.  Specifically, writing of the
fsmonitor extension happens only after the work to split the index
has been applied -- as such, the information in the index is only
for the non-"base" index, and thus the extension information
contains only partial data.

When saving, compute the ewah bitmap before the index is split, and
store it in the fsmonitor_dirty field, mirroring the behavior that
occurred during reading.  fsmonitor_dirty is kept from being leaked by
being freed when the extension data is written -- which always happens
precisely once, no matter the split index configuration.

Signed-off-by: Alex Vandiver <alexmv@dropbox.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 8 insertions, 1 deletions

diff --git a/fsmonitor.h b/fsmonitor.h
index 0de644e..cd3cc0c 100644
--- a/fsmonitor.h
+++ b/fsmonitor.h
@@ -10,7 +10,14 @@ extern struct trace_key trace_fsmonitor;
 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.
+ * Fill the fsmonitor_dirty ewah bits with their state from the index,
+ * before it is split during writing.
+ */
+extern void fill_fsmonitor_bitmap(struct index_state *istate);
+
+/*
+ * Write the CE_FSMONITOR_VALID state into the fsmonitor index
+ * extension.  Reads from the fsmonitor_dirty ewah in the index.
  */
 extern void write_fsmonitor_extension(struct strbuf *sb, struct index_state *istate);