On Mon, Oct 10, 2016 at 06:54:08PM +0800, Anand Jain wrote:
> 
> 
> On 10/10/16 17:21, Qu Wenruo wrote:
> > For multi-device btrfs, after UUID change we should info kernel, or new
> > fs can't be mounted due to false alert on missing devices.
> >
> > Signed-off-by: Qu Wenruo <[email protected]>
> > ---
> >  btrfstune.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> >
> > diff --git a/btrfstune.c b/btrfstune.c
> > index 15dde90..23d06ce 100644
> > --- a/btrfstune.c
> > +++ b/btrfstune.c
> > @@ -369,6 +369,15 @@ static int change_uuid(struct btrfs_fs_info *fs_info, 
> > const char *new_fsid_str)
> >     fs_info->new_fsid = NULL;
> >     fs_info->new_chunk_tree_uuid = NULL;
> >     printf("Fsid change finished\n");
> > +
> > +   /*
> > +    * Register new devices, or multi-volume btrfs can't be mounted until
> > +    * device scan happens.
> > +    * Ignore any error, as such register is optional.
> > +    */
> > +   printf("Register new UUIDs(error can be ignored)\n");
> 
>   Whats the error in particular in this context. ?

If /dev/btrfs-control cannot be opened by the user, in
btrfs_register_one_device() .

> > +   btrfs_register_all_devices();
> 
>   That means after a reboot -> change uuid it will register the devices 
> though the devices weren't registered to the kernel before.
> 
>   Its fair enough just remind user to run dev scan so that kernel can 
> see them.

This is similar to mkfs that is not able to register the devices for
the same reason.
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