The intended usage of total_devices and num_devices
should be recorded in the comments so that these
two counters can be used correctly as originally
intended.
As of now there appears to be slight deviations/bugs
from the original intention, the bugs are apparent
that num_devices does not count seed devices where
as total_devices does, but total_devices does not
count the replacing devices where as num_devices does.
So in this situation the ioctl(BTRFS_IOC_DEVICES_READY)
will fails when there is seed FS. Next, applications
using ioctl(BTRFS_IOC_FS_INFO) and ioctl(BTRFS_IOC_DEV_INFO)
in conjunction to allocate the slots will also fail
as former depend on the num_devices where as latter
would match total_devices (except when replace is running).
This patch will help have the clarity on usage
of these two counter so that bugs related to this can
be fixed.
Signed-off-by: Anand Jain <Anand.Jain@xxxxxxxxxx>
---
v2: edit commit
fs/btrfs/volumes.h | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 91b7596..99c71aa 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -121,12 +121,18 @@ struct btrfs_fs_devices {
/* the device with this id has the most recent copy of the super */
u64 latest_devid;
u64 latest_trans;
+ /* num_devices contains run time count of devices which are part
+ * of this FSID. (the FS devices + replacing devices + ?
+ */
u64 num_devices;
u64 open_devices;
u64 rw_devices;
u64 missing_devices;
u64 total_rw_bytes;
u64 num_can_discard;
+ /* total_devices contains static recorded count of device which
+ * are part of this FSID. (the FS devices + seed devices + ?
+ */
u64 total_devices;
struct block_device *latest_bdev;
--
1.8.5.3
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