Merge branch 'rr/minimal-stat'

Some reimplementations of Git does not write all the stat info back
to the index due to their implementation limitations (e.g. jgit
running on Java).  A configuration option can tell Git to ignore
changes to most of the stat fields and only pay attention to mtime
and size, which these implementations can reliably update.  This
avoids excessive revalidation of contents.

* rr/minimal-stat:
  Enable minimal stat checking

Documentation/config.txt

@@ -235,6 +235,12 @@ core.trustctime::
 	crawlers and some backup systems).
 	See linkgit:git-update-index[1]. True by default.
 
+core.checkstat::
+	Determines which stat fields to match between the index
+	and work tree. The user can set this to 'default' or
+	'minimal'. Default (or explicitly 'default'), is to check
+	all fields, including the sub-second part of mtime and ctime.
+
 core.quotepath::
 	The commands that output paths (e.g. 'ls-files',
 	'diff'), when not given the `-z` option, will quote

cache.h

@@ -536,6 +536,7 @@ extern int delete_ref(const char *, const unsigned char *sha1, int delopt);
 /* Environment bits from configuration mechanism */
 extern int trust_executable_bit;
 extern int trust_ctime;
+extern int check_stat;
 extern int quote_path_fully;
 extern int has_symlinks;
 extern int minimum_abbrev, default_abbrev;

config.c

@@ -566,6 +566,12 @@ static int git_default_core_config(const char *var, const char *value)
 		trust_ctime = git_config_bool(var, value);
 		return 0;
 	}
+	if (!strcmp(var, "core.statinfo")) {
+		if (!strcasecmp(value, "default"))
+			check_stat = 1;
+		else if (!strcasecmp(value, "minimal"))
+			check_stat = 0;
+	}
 
 	if (!strcmp(var, "core.quotepath")) {
 		quote_path_fully = git_config_bool(var, value);

environment.c

@@ -13,6 +13,7 @@
 
 int trust_executable_bit = 1;
 int trust_ctime = 1;
+int check_stat = 1;
 int has_symlinks = 1;
 int minimum_abbrev = 4, default_abbrev = 7;
 int ignore_case;

read-cache.c

@@ -197,30 +197,34 @@ static int ce_match_stat_basic(struct cache_entry *ce, struct stat *st)
 	}
 	if (ce->ce_mtime.sec != (unsigned int)st->st_mtime)
 		changed |= MTIME_CHANGED;
-	if (trust_ctime && ce->ce_ctime.sec != (unsigned int)st->st_ctime)
+	if (trust_ctime && check_stat &&
+	    ce->ce_ctime.sec != (unsigned int)st->st_ctime)
 		changed |= CTIME_CHANGED;
 
 #ifdef USE_NSEC
-	if (ce->ce_mtime.nsec != ST_MTIME_NSEC(*st))
+	if (check_stat && ce->ce_mtime.nsec != ST_MTIME_NSEC(*st))
 		changed |= MTIME_CHANGED;
-	if (trust_ctime && ce->ce_ctime.nsec != ST_CTIME_NSEC(*st))
+	if (trust_ctime && check_stat &&
+	    ce->ce_ctime.nsec != ST_CTIME_NSEC(*st))
 		changed |= CTIME_CHANGED;
 #endif
 
-	if (ce->ce_uid != (unsigned int) st->st_uid ||
-	    ce->ce_gid != (unsigned int) st->st_gid)
-		changed |= OWNER_CHANGED;
-	if (ce->ce_ino != (unsigned int) st->st_ino)
-		changed |= INODE_CHANGED;
+	if (check_stat) {
+		if (ce->ce_uid != (unsigned int) st->st_uid ||
+			ce->ce_gid != (unsigned int) st->st_gid)
+			changed |= OWNER_CHANGED;
+		if (ce->ce_ino != (unsigned int) st->st_ino)
+			changed |= INODE_CHANGED;
+	}
 
 #ifdef USE_STDEV
 	/*
 	 * st_dev breaks on network filesystems where different
 	 * clients will have different views of what "device"
 	 * the filesystem is on
 	 */
-	if (ce->ce_dev != (unsigned int) st->st_dev)
-		changed |= INODE_CHANGED;
+	if (check_stat && ce->ce_dev != (unsigned int) st->st_dev)
+			changed |= INODE_CHANGED;
 #endif
 
 	if (ce->ce_size != (unsigned int) st->st_size)