build: generate strictly increasing git revisions (#225)

Instead of simply emitting a "git-$hash" revision, take the commit time into
account to generate strictly increasing revisions to preserve opkg upgrade
capabilities.

The format is "git-YY.DDD.SSSSS-HHHHHHH" with the following defined fields:

  - YY        year number (00..99)
  - DDD       day of year (001..366)
  - SSSSSS    second of day (00000..86399)
  - HHHHHHH   abbreviated git commit hash

An example revision is "git-14.283.50202-bb388f0".

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>

diff --git a/build/mkrevision.sh b/build/mkrevision.sh
index 889ce75..02b7fa3 100755 (executable)
--- a/build/mkrevision.sh
+++ b/build/mkrevision.sh
@@ -14,7 +14,10 @@ TOPDIR="${0%mkrevision.sh}"
        elif git log -1 >/dev/null 2>/dev/null; then
                revision="svn-r$(LC_ALL=C git log -1 | sed -ne 's/.*git-svn-id: .*@\([0-9]\+\) .*/\1/p')"
                if [ "$revision" = "svn-r" ]; then
-                       revision="git-$(LC_ALL=C git log -1 --pretty=%h)"
+                       set -- $(git log -1 --format="%ct %h")
+                       secs="$(($1 % 86400))"
+                       yday="$(date --utc --date="@$1" "+%y.%j")"
+                       revision="$(printf 'git-%s.%05d-%s' "$yday" "$secs" "$2")"
                fi
        else
                revision="unknown"