mergeme: Update mtime if file is equal and introduce ignore-mtime

Updates the mtime per default if the file is equal and adds a new
feature flag called "ignore-mtime" to ignore mtime updates if the
target file is equal.

Signed-off-by: gcarq <[email protected]>

Author: gcarq

lib/portage/const.py

@@ -159,6 +159,7 @@
         "getbinpkg",
         "gpg-keepalive",
         "icecream",
+        "ignore-mtime",
         "installsources",
         "ipc-sandbox",
         "keeptemp",

lib/portage/dbapi/vartree.py

@@ -5422,6 +5422,7 @@ def mergeme(
         srcroot = normalize_path(srcroot).rstrip(sep) + sep
         destroot = normalize_path(destroot).rstrip(sep) + sep
         calc_prelink = "prelink-checksums" in self.settings.features
+        ignore_mtime = "ignore-mtime" in self.settings.features
 
         protect_if_modified = (
             "config-protect-if-modified" in self.settings.features
@@ -5830,6 +5831,13 @@ def mergeme(
                         hardlink_candidates.append(mydest)
                         zing = ">>>"
                     else:
+                        if not ignore_mtime:
+                            mymtime = thismtime if thismtime is not None else mymtime
+                            try:
+                                os.utime(mydest, ns=(mymtime, mymtime))
+                            except OSError:
+                                # utime can fail here with EPERM
+                                pass
                         zing = "==="
 
                     try:

man/make.conf.5

@@ -533,6 +533,10 @@ If your GPG is auto unlocked on login, you do not need this.
 .B icecream
 Enable portage support for the icecream package.
 .TP
+.B ignore\-mtime
+Do not update mtime if the target file is equal. This can be useful on some
+filesystems to better utilize features like snapshots and data duplication.
+.TP
 .B installsources
 Install source code into /usr/src/debug/${CATEGORY}/${PF} (also see
 \fBsplitdebug\fR). This feature works only if debugedit is installed, CFLAGS