Dan Williams [off-list ref] writes:

On Fri, Aug 28, 2015 at 4:27 PM, Song Liu [off-list ref] wrote:

quoted

If journal device is missing, do not start the array, and shows:

./mdadm -I /dev/sdf
mdadm: journal device is missing, not safe to start yet.

The array will be started when the journal device is attached with -I

./mdadm -I /dev/sdb1
mdadm: /dev/sdb1 attached to /dev/md/0_0, which has been started.

To force start without journal device:

./mdadm -I /dev/sdf --run
mdadm: Trying to run with missing journal device
mdadm: /dev/sdf attached to /dev/md/0_0, which has been started.

Signed-off-by: Shaohua Li <redacted>
Signed-off-by: Song Liu <redacted>
---
 Incremental.c | 31 +++++++++++++++++++++++++++----
 1 file changed, 27 insertions(+), 4 deletions(-)

diff --git a/Incremental.c b/Incremental.c
index 304cc6d..74905e3 100644
--- a/Incremental.c
+++ b/Incremental.c

@@ -35,7 +35,7 @@

 static int count_active(struct supertype *st, struct mdinfo *sra,
                        int mdfd, char **availp,
-                       struct mdinfo *info);
+                       struct mdinfo *info, int *journal_device_missing);
 static void find_reject(int mdfd, struct supertype *st, struct mdinfo *sra,
                        int number, __u64 events, int verbose,
                        char *array_name);

@@ -104,6 +104,7 @@ int Incremental(struct mddev_dev *devlist, struct context *c,
        struct map_ent target_array;
        int have_target;
        char *devname = devlist->devname;
+       int journal_device_missing = 0;

        struct createinfo *ci = conf_get_create_info();

@@ -518,7 +519,7 @@ int Incremental(struct mddev_dev *devlist, struct context *c,
        sysfs_free(sra);
        sra = sysfs_read(mdfd, NULL, (GET_DEVS | GET_STATE |
                                    GET_OFFSET | GET_SIZE));
-       active_disks = count_active(st, sra, mdfd, &avail, &info);
+       active_disks = count_active(st, sra, mdfd, &avail, &info, &journal_device_missing);
        if (enough(info.array.level, info.array.raid_disks,
                   info.array.layout, info.array.state & 1,
                   avail) == 0) {

@@ -548,10 +549,12 @@ int Incremental(struct mddev_dev *devlist, struct context *c,
        }

        map_unlock(&map);
-       if (c->runstop > 0 || active_disks >= info.array.working_disks) {
+       if (c->runstop > 0 || (!journal_device_missing && active_disks >= info.array.working_disks)) {

A minor comment, and I'd defer to Neil's opinion, but I think this is
asking for mdu_array_info_t to grow a "journal_disks" attribute.

We definitely don't want to change mdu_array_info_t - that is part of
the kernel api.
But adding a 'journal_disks' field to 'struct mdinfo' might make sense.

Similarly, now that I look at it, the 'require_journal' method doesn't
look like such a good idea.
->getinfo_super should set some flag in 'struct mdinfo' if a journal is
required.

The Incremental() function might still have a local var called
journal_device_missing, but it wouldn't pass it to count_active().
count_active would just set ->journal_disks and then Incrmental would do
something like:

journal_device_missing = info.journal_needed && info.journal_disks == 0;

Song: can you see if making some changes like that works out?

Thanks,
NeilBrown