Support clamping the file mtime to the build time

This makes the file mtime more reproducible and consistent. The
package build time is set before the build is started, so every
new file will get the same time.

build/files.c

@@ -1023,7 +1023,7 @@ static int seenHardLink(FileRecords files, FileListRec flp, rpm_ino_t *fileid)
  * @param pkg		(sub) package
  * @param isSrc		pass 1 for source packages 0 otherwise
  */
-static void genCpioListAndHeader(FileList fl, Package pkg, int isSrc)
+static void genCpioListAndHeader(FileList fl, rpmSpec spec, Package pkg, int isSrc)
 {
     FileListRec flp;
     char buf[BUFSIZ];
@@ -1033,23 +1033,41 @@ static void genCpioListAndHeader(FileList fl, Package pkg, int isSrc)
     rpm_loff_t totalFileSize = 0;
     Header h = pkg->header; /* just a shortcut */
     int override_date = 0;
-    time_t source_date_epoch = 0;
+    time_t mtime_clamp = 0;
     char *srcdate = getenv("SOURCE_DATE_EPOCH");
+    char *mtime_policy_str = rpmExpand("%{?build_mtime_policy}", NULL);
 
-    /* Limit the maximum date to SOURCE_DATE_EPOCH if defined
-     * similar to the tar --clamp-mtime option
-     * https://reproducible-builds.org/specs/source-date-epoch/
-     */
-    if (srcdate && rpmExpandNumeric("%{?clamp_mtime_to_source_date_epoch}")) {
-	char *endptr;
-	errno = 0;
-	source_date_epoch = strtol(srcdate, &endptr, 10);
-	if (srcdate == endptr || *endptr || errno != 0) {
-	    rpmlog(RPMLOG_ERR, _("unable to parse %s=%s\n"), "SOURCE_DATE_EPOCH", srcdate);
-	    fl->processingFailed = 1;
+    /* backward compatibility */
+    if (!*mtime_policy_str) {
+        if (srcdate && rpmExpandNumeric("%{?clamp_mtime_to_source_date_epoch}")) {
+	    free(mtime_policy_str);
+	    mtime_policy_str = xstrdup("clamp_to_source_date_epoch");
 	}
+    }
+
+    if (!strcmp(mtime_policy_str, "clamp_to_buildtime")) {
+	mtime_clamp = spec->buildTime;
 	override_date = 1;
+    } else if (!strcmp(mtime_policy_str, "clamp_to_source_date_epoch")) {
+	/* Limit the maximum date to SOURCE_DATE_EPOCH if defined
+	 * similar to the tar --clamp-mtime option
+	 * https://reproducible-builds.org/specs/source-date-epoch/
+	 */
+	if (srcdate) {
+	    char *endptr;
+	    errno = 0;
+	    mtime_clamp = strtol(srcdate, &endptr, 10);
+	    if (srcdate == endptr || *endptr || errno != 0) {
+		rpmlog(RPMLOG_ERR, _("unable to parse %s=%s\n"), "SOURCE_DATE_EPOCH", srcdate);
+		fl->processingFailed = 1;
+	    }
+	    override_date = 1;
+	}
+    } else if (*mtime_policy_str) {
+	rpmlog(RPMLOG_WARNING,
+		_("Unknown mtime policy '%s'\n"), mtime_policy_str);
     }
+    free(mtime_policy_str);
 
     /*
      * See if non-md5 file digest algorithm is requested. If not
@@ -1192,8 +1210,8 @@ static void genCpioListAndHeader(FileList fl, Package pkg, int isSrc)
 	    }
 	}
 
-	if (override_date && flp->fl_mtime > source_date_epoch) {
-	    flp->fl_mtime = source_date_epoch;
+	if (override_date && flp->fl_mtime > mtime_clamp) {
+	    flp->fl_mtime = mtime_clamp;
 	}
 	/*
  	 * For items whose size varies between systems, always explicitly 
@@ -2652,7 +2670,7 @@ static rpmRC processPackageFiles(rpmSpec spec, rpmBuildPkgFlags pkgFlags,
     if (checkHardLinks(&fl.files))
 	(void) rpmlibNeedsFeature(pkg, "PartialHardlinkSets", "4.0.4-1");
 
-    genCpioListAndHeader(&fl, pkg, 0);
+    genCpioListAndHeader(&fl, spec, pkg, 0);
 
 exit:
     FileListFree(&fl);
@@ -2782,7 +2800,7 @@ rpmRC processSourceFiles(rpmSpec spec, rpmBuildPkgFlags pkgFlags)
 
     if (! fl.processingFailed) {
 	if (sourcePkg->header != NULL) {
-	    genCpioListAndHeader(&fl, sourcePkg, 1);
+	    genCpioListAndHeader(&fl, spec, sourcePkg, 1);
 	}
     }
 

macros.in

@@ -240,10 +240,12 @@ Supplements:   (%{name} = %{version}-%{release} and langpacks-%{1})\
 #	Is ignored when SOURCE_DATE_EPOCH is not set.
 %use_source_date_epoch_as_buildtime 0
 
-#	If true, make sure that timestamps in built rpms
-#	are not later than the value of SOURCE_DATE_EPOCH.
-#	Is ignored when SOURCE_DATE_EPOCH is not set.
-%clamp_mtime_to_source_date_epoch 0
+#	Defines file timestamp handling in built rpms. Possible values
+#       are "clamp_to_buildtime" and "clamp_to_source_date_epoch", 
+#       which makes sure the the file timestamps are not later than
+#       the build time of the package or the value of
+#       SOURCE_DATE_EPOCH, respectively.
+#%build_mtime_policy
 
 #	If enabled, dilute user() and group() requires into recommends
 #%_use_weak_usergroup_deps 1