[PATCH 03/24] read-cache.c: new flag for add_index_entry() to write to backup log

From

Nguyễn Thái Ngọc Duy <pclouds@gmail.com>

Date

Dec 9, 2018, 10:43 UTC

Message-ID

<20181209104419.12639-4-pclouds@gmail.com>

In-Reply-To

<20181209104419.12639-1-pclouds@gmail.com>

Note, we do double locking when writing $GIT_DIR/index now:

- $GIT_DIR/index.lock is created
- then $GIT_DIR/index.bkl.lock is created

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 cache.h      |  2 ++
 read-cache.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 49 insertions(+), 2 deletions(-)

diff --git a/cache.h b/cache.h
index ca36b44ee0..51ffae7961 100644
--- a/cache.h
+++ b/cache.h
@@ -336,6 +336,7 @@ struct index_state {
 	uint64_t fsmonitor_last_update;
 	struct ewah_bitmap *fsmonitor_dirty;
 	struct mem_pool *ce_mem_pool;
+	struct strbuf *backup_log;
 };
 
 extern struct index_state the_index;
@@ -745,6 +746,7 @@ extern int index_name_pos(const struct index_state *, const char *name, int name
 #define ADD_CACHE_JUST_APPEND 8		/* Append only; tree.c::read_tree() */
 #define ADD_CACHE_NEW_ONLY 16		/* Do not replace existing ones */
 #define ADD_CACHE_KEEP_CACHE_TREE 32	/* Do not invalidate cache-tree */
+#define ADD_CACHE_LOG_UPDATES 64	/* Log changes in $GIT_DIR/index.bkl */
 extern int add_index_entry(struct index_state *, struct cache_entry *ce, int option);
 extern void rename_index_entry_at(struct index_state *, int pos, const char *new_name);
 
diff --git a/read-cache.c b/read-cache.c
index bd45dc3e24..a53cfabc2e 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -25,6 +25,7 @@
 #include "fsmonitor.h"
 #include "thread-utils.h"
 #include "progress.h"
+#include "backup-log.h"
 
 /* Mask for the name length in ce_flags in the on-disk index */
 
@@ -691,6 +692,21 @@ void set_object_name_for_intent_to_add_entry(struct cache_entry *ce)
 	oidcpy(&ce->oid, &oid);
 }
 
+static void update_backup_log(struct index_state *istate,
+			      const struct object_id *prev,
+			      const struct cache_entry *ce)
+{
+	struct strbuf *sb = istate->backup_log;
+
+	if (!sb) {
+		sb = xmalloc(sizeof(*sb));
+		strbuf_init(sb, 0);
+		istate->backup_log = sb;
+	}
+
+	bkl_append(sb, ce->name, prev, &ce->oid);
+}
+
 int add_to_index(struct index_state *istate, const char *path, struct stat *st, int flags)
 {
 	int namelen, was_same;
@@ -765,6 +781,7 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
 			discard_cache_entry(ce);
 			return error("unable to index file %s", path);
 		}
+		add_option |= flags & ADD_CACHE_LOG_UPDATES;
 	} else
 		set_object_name_for_intent_to_add_entry(ce);
 
@@ -1257,6 +1274,7 @@ static int add_index_entry_with_check(struct index_state *istate, struct cache_e
 	int ok_to_replace = option & ADD_CACHE_OK_TO_REPLACE;
 	int skip_df_check = option & ADD_CACHE_SKIP_DFCHECK;
 	int new_only = option & ADD_CACHE_NEW_ONLY;
+	struct object_id backup_prev;
 
 	if (!(option & ADD_CACHE_KEEP_CACHE_TREE))
 		cache_tree_invalidate_path(istate, ce->name);
@@ -1273,8 +1291,12 @@ static int add_index_entry_with_check(struct index_state *istate, struct cache_e
 
 	/* existing match? Just replace it. */
 	if (pos >= 0) {
-		if (!new_only)
-			replace_index_entry(istate, pos, ce);
+		if (new_only)
+			return 0;
+
+		if (option & ADD_CACHE_LOG_UPDATES)
+			update_backup_log(istate, &istate->cache[pos]->oid, ce);
+		replace_index_entry(istate, pos, ce);
 		return 0;
 	}
 	pos = -pos-1;
@@ -1282,6 +1304,7 @@ static int add_index_entry_with_check(struct index_state *istate, struct cache_e
 	if (!(option & ADD_CACHE_KEEP_CACHE_TREE))
 		untracked_cache_add_to_index(istate, ce->name);
 
+	oidclr(&backup_prev);
 	/*
 	 * Inserting a merged entry ("stage 0") into the index
 	 * will always replace all non-merged entries..
@@ -1289,6 +1312,8 @@ static int add_index_entry_with_check(struct index_state *istate, struct cache_e
 	if (pos < istate->cache_nr && ce_stage(ce) == 0) {
 		while (ce_same_name(istate->cache[pos], ce)) {
 			ok_to_add = 1;
+			if (ce_stage(ce) == 2)
+				oidcpy(&backup_prev, &istate->cache[pos]->oid);
 			if (!remove_index_entry_at(istate, pos))
 				break;
 		}
@@ -1307,6 +1332,8 @@ static int add_index_entry_with_check(struct index_state *istate, struct cache_e
 		pos = index_name_stage_pos(istate, ce->name, ce_namelen(ce), ce_stage(ce));
 		pos = -pos-1;
 	}
+	if (option & ADD_CACHE_LOG_UPDATES)
+		update_backup_log(istate, &backup_prev, ce);
 	return pos + 1;
 }
 
@@ -2323,6 +2350,10 @@ int discard_index(struct index_state *istate)
 	discard_split_index(istate);
 	free_untracked_cache(istate->untracked);
 	istate->untracked = NULL;
+	if (istate->backup_log) {
+		strbuf_release(istate->backup_log);
+		FREE_AND_NULL(istate->backup_log);
+	}
 
 	if (istate->ce_mem_pool) {
 		mem_pool_discard(istate->ce_mem_pool, should_validate_cache_entries());
@@ -3157,6 +3188,20 @@ int write_locked_index(struct index_state *istate, struct lock_file *lock,
 	if (istate->fsmonitor_last_update)
 		fill_fsmonitor_bitmap(istate);
 
+	if (istate->backup_log && istate->backup_log->len) {
+		struct strbuf sb = STRBUF_INIT;
+		char *path = get_locked_file_path(lock);
+
+		strbuf_addf(&sb, "%s.bkl", path);
+		free(path);
+		if (bkl_write(sb.buf, istate->backup_log)) {
+			strbuf_release(&sb);
+			return -1;
+		}
+		strbuf_reset(istate->backup_log);
+		strbuf_release(&sb);
+	}
+
 	if (!si || alternate_index_output ||
 	    (istate->cache_changed & ~EXTMASK)) {
 		if (si)

-- 
2.20.0.rc2.486.g9832c05c3d