test case:
disappear a disk then replace (RAID1) the disappeared disk
and then make disappeared disk to reappear.
----
mkfs.btrfs -f -m raid1 -d raid1 /dev/sdc /dev/sdd
mount /dev/sdc /btrfs
dd if=/dev/zero of=/btrfs/tf1 count=1
btrfs fi sync /btrfs
---
devmgt[1] will help to attach or detach a disk easily
--
devmgt show
devmgt detach /dev/sdc
--
btrfs sill unaware of device missing.
--
btrfs fi show -m
Label: none uuid: 5dc0aaf4-4683-4050-b2d6-5ebe5f5cd120
Total devices 2 FS bytes used 32.00KiB
devid 1 size 958.94MiB used 115.88MiB path /dev/sdc <--
devid 2 size 958.94MiB used 103.88MiB path /dev/sdd
btrfs rep start -f 1 /dev/sde /btrfs
Label: none uuid: 5dc0aaf4-4683-4050-b2d6-5ebe5f5cd120
Total devices 2 FS bytes used 32.00KiB
devid 1 size 958.94MiB used 115.88MiB path /dev/sde
devid 2 size 958.94MiB used 103.88MiB path /dev/sdd
--
so far good. now missing /dev/sdc comes-back.
---
devmgt attach host2
btrfs fi show -m shows sdc
Label: none uuid: 5dc0aaf4-4683-4050-b2d6-5ebe5f5cd120^M
Total devices 2 FS bytes used 32.00KiB^M
devid 1 size 958.94MiB used 115.88MiB path /dev/sdc <- Wrong.
devid 2 size 958.94MiB used 103.88MiB path /dev/sdd
---
this is wrong it should be sde. this happened because when
disk comes back device_list_add() is called which would invariably
replace the existing disk with the given disk with the same fsid/devid.
But the actual IO is still going to sde not to sdc.
Further when we start fresh with (modprobe -r btrfs)
unless it is carefully managed using btrfs dev scan <dev>
it may pair with wrong disk.
Need your review of the following proposed fix. This patch
will compare the trans id before disk is substituted.
----------------------------------------------------
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 2ca91fc..b226284 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -496,14 +496,39 @@ static noinline int device_list_add(const char *path,
device->fs_devices = fs_devices;
} else if (!device->name || strcmp(device->name->str, path)) {
- name = rcu_string_strdup(path, GFP_NOFS);
- if (!name)
- return -ENOMEM;
- rcu_string_free(device->name);
- rcu_assign_pointer(device->name, name);
- if (device->missing) {
- fs_devices->missing_devices--;
- device->missing = 0;
+
+ struct buffer_head *bh;
+ struct btrfs_super_block *cur_disk_super;
+ u64 cur_transid;
+
+ if (!device->missing) {
+ bh = btrfs_read_dev_super(device->bdev);
+ if (!bh)
+ return -EINVAL;
+
+ cur_disk_super = (struct btrfs_super_block *)
+ bh->b_data;
+ cur_transid = btrfs_super_generation(ds);
+ } else
+ cur_transid = 0;
+
+ if (found_transid > cur_transid) {
+
+ name = rcu_string_strdup(path, GFP_NOFS);
+ if (!name)
+ return -ENOMEM;
+
+ rcu_string_free(device->name);
+ rcu_assign_pointer(device->name, name);
+
+ if (device->missing) {
+ fs_devices->missing_devices--;
+ device->missing = 0;
+ }
+
+ printk_in_rcu(KERN_INFO "%s tran %llu replaced %s tran %llu\n",
+ path, found_transid,
+ rcu_str_deref(device->name), tranid);
}
}
---------------------------------------
Thanks Anand
[1] github.com/anajain/devmgt.git
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