On Thu, Aug 02, 2018 at 01:11:40PM +0300, Nikolay Borisov wrote:
>
>
> On 2.08.2018 13:09, Anand Jain wrote:
> > When the replace is running the fs_devices::num_devices also includes
> > the replace device, however in some operations like device delete and
> > balance it needs the actual num_devices without the repalce devices, so
> > now the function btrfs_num_devices() just provides that.
> >
> > And here is a scenario how balance and repalce items could co-exist.
> > Consider balance is started and paused, now start the replace
> > followed by a power-recycle of the system. During following mount,
> > the open_ctree() first restarts the balance so it must check for the
> > replace device otherwise our num_devices calculation will be wrong.
> >
> > Signed-off-by: Anand Jain <anand.j...@oracle.com>
> > ---
> > v2->v3: update changelog with not so obvious balance and repalce
> > co-existance secnario
> > v1->v2: add comments
> >
> > fs/btrfs/volumes.c | 32 ++++++++++++++++++--------------
> > 1 file changed, 18 insertions(+), 14 deletions(-)
> >
> > diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> > index fe74fefc75f7..8844904f9009 100644
> > --- a/fs/btrfs/volumes.c
> > +++ b/fs/btrfs/volumes.c
> > @@ -1854,6 +1854,21 @@ void btrfs_assign_next_active_device(struct
> > btrfs_device *device,
> > fs_info->fs_devices->latest_bdev = next_device->bdev;
> > }
> >
> > +/* Returns btrfs_fs_devices::num_devices excluding replace device if any */
> > +static inline u64 btrfs_num_devices(struct btrfs_fs_info *fs_info)
This does not need to be static inline, it's not in a header.
> > +{
> > + u64 num_devices = fs_info->fs_devices->num_devices;
> > +
> > + btrfs_dev_replace_read_lock(&fs_info->dev_replace);
> > + if (btrfs_dev_replace_is_ongoing(&fs_info->dev_replace)) {
> > + BUG_ON(num_devices < 1);
> > + num_devices--;
> > + }
> > + btrfs_dev_replace_read_unlock(&fs_info->dev_replace);
> > +
> > + return num_devices;
> > +}
> > +
> > int btrfs_rm_device(struct btrfs_fs_info *fs_info, const char *device_path,
> > u64 devid)
> > {
> > @@ -1865,13 +1880,7 @@ int btrfs_rm_device(struct btrfs_fs_info *fs_info,
> > const char *device_path,
> >
> > mutex_lock(&uuid_mutex);
> >
> > - num_devices = fs_devices->num_devices;
> > - btrfs_dev_replace_read_lock(&fs_info->dev_replace);
> > - if (btrfs_dev_replace_is_ongoing(&fs_info->dev_replace)) {
> > - BUG_ON(num_devices < 1);
> > - num_devices--;
> > - }
> > - btrfs_dev_replace_read_unlock(&fs_info->dev_replace);
> > + num_devices = btrfs_num_devices(fs_info);
>
> How about lifting the BUG_ON from btrfs_num_devices into a check in this
> function, so if num_devices < 1 then we just exit with -EINVAL or some
> such. We should be aiming at eliminating BUG_ONs.
Right, in both cases it's possible to return with an error instead of
the BUG_ON.
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