Introduce --no-resume.

If the dss daemon (or the rsync process) is killed while a snaphot
is being created, e.g. because of a server shutdown, the latest
snapshot remains incomplete until it is removed by the usual shapshot
pruning mechanism.

This patch changes the snapshot creation behaviour if the
most recently created snapshot happens to be incomplete and the
new --no-resume option is not given. In this case the directory
of the incomplete snapshot is reused as the destination directory
for the the new snapshot.

This change saves disk space and reduces the snapshot creation time,
depending of course on how far the previous rsync process got before
it was interrupted.

diff --git a/dss.c b/dss.c
index 93ab802cb123bddde776042a9a9cff266102091c..eae8b3ed0f2ea112a54c3d6356329c9f6e768441 100644 (file)
--- a/dss.c
+++ b/dss.c
@@ -966,6 +966,32 @@ static int use_rsync_locally(char *logname)
        return 1;
 }
 
+static int rename_resume_snap(int64_t creation_time)
+{
+       struct snapshot_list sl = {.num_snapshots = 0};
+       struct snapshot *s;
+       char *new_name = incomplete_name(creation_time);
+       int ret;
+
+       ret = 0;
+       if (conf.no_resume_given)
+               goto out;
+       dss_get_snapshot_list(&sl);
+       s = get_newest_snapshot(&sl);
+       if (!s)
+               goto out;
+       if ((s->flags & SS_COMPLETE) != 0) /* complete */
+               goto out;
+       DSS_INFO_LOG("resuming: reusing %s as destination dir\n", s->name);
+       ret = dss_rename(s->name, new_name);
+out:
+       if (ret >= 0)
+               DSS_NOTICE_LOG("creating new snapshot %s\n", new_name);
+       free(new_name);
+       free_snapshot_list(&sl);
+       return ret;
+}
+
 static void create_rsync_argv(char ***argv, int64_t *num)
 {
        char *logname;
@@ -1018,11 +1044,10 @@ static void free_rsync_argv(char **argv)
 static int create_snapshot(char **argv)
 {
        int ret, fds[3] = {0, 0, 0};
-       char *name;
 
-       name = incomplete_name(current_snapshot_creation_time);
-       DSS_NOTICE_LOG("creating new snapshot %s\n", name);
-       free(name);
+       ret = rename_resume_snap(current_snapshot_creation_time);
+       if (ret < 0)
+               return ret;
        ret = dss_exec(&create_pid, argv[0], argv, fds);
        if (ret < 0)
                return ret;

diff --git a/dss.ggo b/dss.ggo
index 506fbf105433fed61631ad965e5b8295068cbfe7..09e345d8db8f270de4182cda8d6033b236407724 100644 (file)
--- a/dss.ggo
+++ b/dss.ggo
@@ -194,6 +194,21 @@ details="
        dss.
 "
 
+option "no-resume" -
+#~~~~~~~~~~~~~~~~~~~
+"Do not try to resume from previous runs"
+flag off
+details = "
+       Starting from version 0.1.4, dss tries to resume from a
+       previously cancelled dss instance by default. It does so by
+       looking at the status of the most recently created snapshot. If
+       this snapshot status is incomplete, its directory is reused
+       as the destination directory for a subsequent rsync run.
+
+       The --no-resume option deactivates this feature so that a new
+       directory is always used as the rsync destination directory.
+"
+
 option "rsync-option" O
 #~~~~~~~~~~~~~~~~~~~~~~
 "Further rsync options"