Add ability to not save mtime in metadata files

If you're storing metadata in a version control system with multiple
branches, mtime differences are going to produce a whole bunch of
conflicts that you likely don't care about. This allows you to not
save mtime and avoid those.

Note that we use a sentinel value of -1 for the mentry `mtimensec` field
to indicate this in the data, as all values of `mtime` are theoretically
valid, but `mtimensec` must always be between 0 and 999,999,999 in the
real world.

I'm not 100% sure about the mechanism for selecting this feature. The
legacy behaviour for metastore was to save mtimes in the metadata files,
but ignore them for compare/apply by default, with a `--mtime` option to
use the mtime data.

Keeping the legacy behaviour for backwards compatibility, but adding a
`--no-mtime` option to ignore mtimes when saving felt like a reasonable
way of making this happen, but something about it doesn't feel great.

Maybe I just didn't figure out how to make the documentation clear
enough.  ¯\_(ツ)_/¯

8 files changed, 109 insertions, 69 deletions

diff --git a/FILEFORMAT_1 b/FILEFORMAT_1
index 189cc84..89d2a86 100644
--- a/FILEFORMAT_1
+++ b/FILEFORMAT_1
@@ -29,6 +29,7 @@ Following sections explain internals of metastore file (.metadata), version 1
                                 i.e. File type and mode, as per inode(7)
     "\t" URLSTRING      - Mtime (including nanoseconds) in ISO-8601 format, UTC.
                                 "YYYY-mm-ddTHH:MM:SS.nnnnnnnnnZ"
+                                Or a literal "0" if mtime is not saved
 
     m * ("\t" URLSTRING "\t" URLSTRING)
                         - xattr name/value pairs. `m` may be 0.
diff --git a/man1/metastore.1 b/man1/metastore.1
index 1e01daf..ee01dd8 100644
--- a/man1/metastore.1
+++ b/man1/metastore.1
@@ -51,6 +51,9 @@ once for even less verbosity.
 .B \-m, \-\-mtime
 Causes metastore to also take mtime into account for the compare or apply actions.
 .TP
+.B \-M, \-\-no\-mtime
+Causes metastore to not save mtime in the metadata
+.TP
 .B \-e, \-\-empty\-dirs
 Also attempts to recreate missing empty directories. May be useful where
 empty directories are not tracked (e.g. by git or cvs).
@@ -108,7 +111,7 @@ in
 and
 .I mtime
 is the ISO-8601 extended format representation of the last-modified time in UTC,
-with nanosecond precision.
+with nanosecond precision, or a literal "0" if mtime is not saved.
 
 Strings are URL-encoded, and all characters from 0x00 to 0x20 (inclusive), 0x25
 (%) and 0x7F \fBmust\fR be encoded.
diff --git a/metastore.txt b/metastore.txt
index 39fdf5e..ba81a05 100644
--- a/metastore.txt
+++ b/metastore.txt
@@ -54,6 +54,9 @@ OPTIONS
               Causes metastore to also take mtime into account for the compare
               or apply actions.
 
+       -M, --no-mtime
+              Causes metastore to not save mtime in the metadata
+
        -e, --empty-dirs
               Also attempts to recreate missing empty directories. May be use‐
               ful  where  empty  directories  are  not tracked (e.g. by git or
@@ -100,7 +103,7 @@ FORMATS
               resentation of the 16-bit "file type and mode"  field  described
               in inode(7), and mtime is the ISO-8601 extended format represen‐
               tation of the last-modified time in UTC, with nanosecond  preci‐
-              sion.
+              sion, or a literal "0" if mtime is not saved.
 
               Strings  are  URL-encoded,  and all characters from 0x00 to 0x20
               (inclusive), 0x25 (%) and 0x7F must be encoded.
diff --git a/src/metaentry.c b/src/metaentry.c
index 7f1012f..9956f7f 100644
--- a/src/metaentry.c
+++ b/src/metaentry.c
@@ -193,7 +193,7 @@ mentries_print(const struct metahash *mhash)
 
 /* Creates a metaentry for the file/dir/etc at path */
 struct metaentry *
-mentry_create(const char *path)
+mentry_create(const char *path, int with_mtime)
 {
 #if !defined(NO_XATTR) || !(NO_XATTR+0)
 	ssize_t lsize, vsize;
@@ -233,8 +233,14 @@ mentry_create(const char *path)
 	mentry->owner = xstrdup(pbuf->pw_name);
 	mentry->group = xstrdup(gbuf->gr_name);
 	mentry->mode = sbuf.st_mode & 0177777;
-	mentry->mtime = sbuf.st_mtim.tv_sec;
-	mentry->mtimensec = sbuf.st_mtim.tv_nsec;
+	if (with_mtime) {
+		mentry->mtime = sbuf.st_mtim.tv_sec;
+		mentry->mtimensec = sbuf.st_mtim.tv_nsec;
+	}
+	else {
+		mentry->mtime = 0;
+		mentry->mtimensec = MTIME_NONE;
+	}
 
 	/* symlinks have no xattrs */
 	if (S_ISLNK(mentry->mode))
@@ -364,7 +370,7 @@ mentries_recurse(const char *path, struct metahash *mhash, msettings *st)
 		return;
 	}
 
-	mentry = mentry_create(path);
+	mentry = mentry_create(path, st->do_mtime >= 0);
 	if (!mentry)
 		return;
 
@@ -491,12 +497,17 @@ mentries_tofile_v1(const struct metahash *mhash, FILE * to)
 		fprintf(to, "%.6o", mentry->mode);
 
 		fputc('\t', to);
-		gmtime_r(&mentry->mtime, &tm);
-		strftime(tmbuf, sizeof(tmbuf), "%Y-%m-%dT%H:%M:%S", &tm);
-		fputs(tmbuf, to);
+		if (mentry->mtimensec != MTIME_NONE) {
+			gmtime_r(&mentry->mtime, &tm);
+			strftime(tmbuf, sizeof(tmbuf), "%Y-%m-%dT%H:%M:%S", &tm);
+			fputs(tmbuf, to);
 
-		fputc('.', to);
-		fprintf(to, "%.9ldZ", mentry->mtimensec);
+			fputc('.', to);
+			fprintf(to, "%.9ldZ", mentry->mtimensec);
+		}
+		else {
+			fputc('0', to);
+		}
 
 		for (i = 0; i < mentry->xattrs; i++) {
 			fputc('\t', to);
@@ -625,50 +636,55 @@ mentries_fromfile_v1(struct metahash **mhash, const char *ptr, const char *max)
 			goto err;
 		if ((mtime = read_string_url(&ptr, max)) == NULL)
 			goto err;
-
-		/* Get the time_t part of `mtime` into mentry->mtime */
-		if ((nsec = strptime(mtime, "%Y-%m-%dT%H:%M:%S", &tm)) == NULL)
-			goto err;
-		tm.tm_isdst = 0;
-		mentry->mtime = timegm(&tm);
-
-		/* Check if there's a nanosecond portion of `mtime` */
-		if (*nsec == '.') {
-			/* There is a decimal point in mtime. Get nanoseconds. */
-			++nsec;
-			mentry->mtimensec = strtol(nsec, &tz, 10);
-			i = tz - nsec;
-			while (i < 9) {
-				/* Too few digits for nanosecond precision.
-				 * e.g. "...T10:15:23.5", which we've parsed as
-				 * 5 nanoseconds, but is actually half a second
-				 * or 500000000 nanoseconds.
-				 * Scale to correct value.
-				 */
-				mentry->mtimensec *= 10;
-				++i;
-			}
-			while (i > 9) {
-				/* Too many digits for nanosecond precision.
-				 * Scale to correct value
-				 */
-				mentry->mtimensec /= 10;
-				--i;
-			}
+		if (strcmp(mtime, "0") == 0) {
+			mentry->mtime = 0;
+			mentry->mtimensec = MTIME_NONE;
 		}
 		else {
-			/* No decimal point. Set nanoseconds to zero */
-			mentry->mtimensec = 0;
-			tz = nsec;
-		}
+			/* Get the time_t part of `mtime` into mentry->mtime */
+			if ((nsec = strptime(mtime, "%Y-%m-%dT%H:%M:%S", &tm)) == NULL)
+				goto err;
+			tm.tm_isdst = 0;
+			mentry->mtime = timegm(&tm);
+
+			/* Check if there's a nanosecond portion of `mtime` */
+			if (*nsec == '.') {
+				/* There is a decimal point in mtime. Get nanoseconds. */
+				++nsec;
+				mentry->mtimensec = strtol(nsec, &tz, 10);
+				i = tz - nsec;
+				while (i < 9) {
+					/* Too few digits for nanosecond precision.
+					 * e.g. "...T10:15:23.5", which we've parsed as
+					 * 5 nanoseconds, but is actually half a second
+					 * or 500000000 nanoseconds.
+					 * Scale to correct value.
+					 */
+					mentry->mtimensec *= 10;
+					++i;
+				}
+				while (i > 9) {
+					/* Too many digits for nanosecond precision.
+					 * Scale to correct value
+					 */
+					mentry->mtimensec /= 10;
+					--i;
+				}
+			}
+			else {
+				/* No decimal point. Set nanoseconds to zero */
+				mentry->mtimensec = 0;
+				tz = nsec;
+			}
 
-		/* Check for a 'Z' (Zulu/UTC) timesone specifier in `mtime`. */
-		if (*tz == 'Z')
-			++tz;
+			/* Check for a 'Z' (Zulu/UTC) timesone specifier in `mtime`. */
+			if (*tz == 'Z')
+				++tz;
 
-		/* Check that we've reached the end of `mtime` */
-		if (*tz != '\0')
-			goto err;
+			/* Check that we've reached the end of `mtime` */
+			if (*tz != '\0')
+				goto err;
+		}
 		free(mtime);
 		mtime = NULL;
 
@@ -842,10 +858,12 @@ mentry_compare(struct metaentry *left, struct metaentry *right, msettings *st)
 	if ((left->mode & S_IFMT) != (right->mode & S_IFMT))
 		retval |= DIFF_TYPE;
 
-	if (st->do_mtime && strcmp(left->path, st->metafile) &&
-	    (   left->mtime     != right->mtime
-	     || left->mtimensec != right->mtimensec)
-	   )
+	if (st->do_mtime > 0
+			&& left->mtimensec != MTIME_NONE
+			&& right->mtimensec != MTIME_NONE
+			&& strcmp(left->path, st->metafile)
+			&& (left->mtime != right->mtime
+				|| left->mtimensec != right->mtimensec))
 		retval |= DIFF_MTIME;
 
 	if (mentry_compare_xattr(left, right)) {
@@ -898,19 +916,28 @@ mentries_dump(struct metahash *mhash)
 	const struct metaentry *mentry;
 	char mode[11 + 1] = "";
 	char date[12 + 2 + 2 + 2*1 + 1 + 2 + 2 + 2 + 2*1 + 1] = "";
-	char zone[5 + 1] = "";
+	char nsec[1 + 9 + 1] = "";
+	char zone[1 + 5 + 1] = "";
 	struct tm cal;
 
 	for (int key = 0; key < HASH_INDEXES; key++) {
 		for (mentry = mhash->bucket[key]; mentry; mentry = mentry->next) {
 			strmode(mentry->mode, mode);
-			localtime_r(&mentry->mtime, &cal);
-			strftime(date, sizeof(date), "%F %T", &cal);
-			strftime(zone, sizeof(zone), "%z", &cal);
-			printf("%s\t%s\t%s\t%s.%09ld %s\t%s%s\n",
+			if (mentry->mtimensec == MTIME_NONE) {
+				snprintf(date, sizeof(date), "%19s", "");
+				snprintf(nsec, sizeof(nsec), "%10s", "");
+				snprintf(zone, sizeof(zone), "%6s", "");
+			}
+			else {
+				localtime_r(&mentry->mtime, &cal);
+				strftime(date, sizeof(date), "%F %T", &cal);
+				snprintf(nsec, sizeof(nsec), ".%09ld", mentry->mtimensec);
+				strftime(zone, sizeof(zone), " %z", &cal);
+			}
+			printf("%s\t%s\t%s\t%s%s%s\t%s%s\n",
 			       mode,
 			       mentry->owner, mentry->group,
-			       date, mentry->mtimensec, zone,
+			       date, nsec, zone,
 			       mentry->path, S_ISDIR(mentry->mode) ? "/" : "");
 			for (unsigned i = 0; i < mentry->xattrs; i++) {
 				printf("\t\t\t\t%s%s\t%s=",
diff --git a/src/metaentry.h b/src/metaentry.h
index a6de66b..6c97961 100644
--- a/src/metaentry.h
+++ b/src/metaentry.h
@@ -54,7 +54,7 @@ struct metahash {
 };
 
 /* Create a metaentry for the file/dir/etc at path */
-struct metaentry *mentry_create(const char *path);
+struct metaentry *mentry_create(const char *path, int with_mtime);
 
 /* Recurses opath and adds metadata entries to the metaentry list */
 void mentries_recurse_path(const char *opath, struct metahash **mhash,
diff --git a/src/metastore.c b/src/metastore.c
index 2bc2a89..bc5787e 100644
--- a/src/metastore.c
+++ b/src/metastore.c
@@ -43,7 +43,7 @@
 /* metastore settings */
 static struct metasettings settings = {
 	.metafile = METAFILE,
-	.do_mtime = false,
+	.do_mtime = 0,
 	.do_emptydirs = false,
 	.do_removeemptydirs = false,
 	.do_git = false,
@@ -286,7 +286,7 @@ compare_fix(struct metaentry *real, struct metaentry *stored, int cmp)
  * recreating them.
  */
 static void
-fixup_emptydirs(void)
+fixup_emptydirs(int do_mtime)
 {
 	struct metaentry *entry;
 	struct metaentry *cur;
@@ -364,7 +364,7 @@ fixup_emptydirs(void)
 		}
 		msg(MSG_QUIET, "ok\n");
 
-		new = mentry_create(cur->path);
+		new = mentry_create(cur->path, do_mtime >= 0);
 		if (!new) {
 			msg(MSG_QUIET, "Failed to get metadata for %s\n", cur->path);
 			continue;
@@ -459,6 +459,7 @@ usage(const char *arg0, const char *message)
 "  -v, --verbose            Print more verbose messages\n"
 "  -q, --quiet              Print less verbose messages\n"
 "  -m, --mtime              Also take mtime into account for diff or apply\n"
+"  -M, --no-mtime           Do not save mtime into metadata\n"
 "  -e, --empty-dirs         Recreate missing empty directories\n"
 "  -E, --remove-empty-dirs  Remove extra empty directories\n"
 "  -g, --git                Do not omit .git directories\n"
@@ -480,6 +481,7 @@ static struct option long_options[] = {
 	{ "verbose",           no_argument,       NULL, 'v' },
 	{ "quiet",             no_argument,       NULL, 'q' },
 	{ "mtime",             no_argument,       NULL, 'm' },
+	{ "no-mtime",          no_argument,       NULL, 'M' },
 	{ "empty-dirs",        no_argument,       NULL, 'e' },
 	{ "remove-empty-dirs", no_argument,       NULL, 'E' },
 	{ "git",               no_argument,       NULL, 'g' },
@@ -501,7 +503,7 @@ main(int argc, char **argv)
 	i = 0;
 	while (1) {
 		int option_index = 0;
-		c = getopt_long(argc, argv, "csadVhvqmeEgf:r:",
+		c = getopt_long(argc, argv, "csadVhvqmMeEgf:r:",
 		                long_options, &option_index);
 		if (c == -1)
 			break;
@@ -514,7 +516,8 @@ main(int argc, char **argv)
 		case 'h': /* help */              action |= ACTION_HELP;  i++;   break;
 		case 'v': /* verbose */           adjust_verbosity(1);           break;
 		case 'q': /* quiet */             adjust_verbosity(-1);          break;
-		case 'm': /* mtime */             settings.do_mtime = true;      break;
+		case 'm': /* mtime */             settings.do_mtime = 1;         break;
+		case 'M': /* no-mtime */          settings.do_mtime = -1;        break;
 		case 'e': /* empty-dirs */        settings.do_emptydirs = true;  break;
 		case 'E': /* remove-empty-dirs */ settings.do_removeemptydirs = true;
 			                              break;
@@ -577,7 +580,7 @@ main(int argc, char **argv)
 	case ACTION_APPLY:
 		mentries_compare(real, stored, compare_fix, &settings);
 		if (settings.do_emptydirs)
-			fixup_emptydirs();
+			fixup_emptydirs(settings.do_mtime);
 		if (settings.do_removeemptydirs)
 			fixup_newemptydirs();
 		break;
diff --git a/src/metastore.h b/src/metastore.h
index bd79416..de51292 100644
--- a/src/metastore.h
+++ b/src/metastore.h
@@ -28,6 +28,9 @@
 #define VERSION_1    "00000001"
 #define VERSIONLEN   8
 
+/* Sentinel value to determine if mtime is not in use */
+#define MTIME_NONE	-1
+
 /* Default filename */
 #define METAFILE     "./.metadata"
 
diff --git a/src/settings.h b/src/settings.h
index 048f281..fd0a0a3 100644
--- a/src/settings.h
+++ b/src/settings.h
@@ -23,7 +23,7 @@
 /* Data structure to hold metastore settings */
 struct metasettings {
 	char *metafile;          /* path to the file containing the metadata */
-	bool do_mtime;           /* should mtimes be corrected? */
+	int do_mtime;            /* deal with mtimes? -1 = no, 0 = default, 1 = yes */
 	bool do_emptydirs;       /* should empty dirs be recreated? */
 	bool do_removeemptydirs; /* should new empty dirs be removed? */
 	bool do_git;             /* should .git dirs be processed? */