On Thu, Sep 12, 2019 at 07:55:01PM -0400, Zygo Blaxell wrote: > Currently, the command: > > btrfs balance start -dconvert=single,soft . > > on a Raspberry Pi produces the following kernel message: > > BTRFS error (device mmcblk0p2): balance: invalid convert data profile single > > This fails because we use is_power_of_2(unsigned long) to validate > the new data profile, the constant for 'single' profile uses bit 48, > and there are only 32 bits in a long on ARM. > > Fix by open-coding the check using u64 variables. > > Tested by completing the original balance command on several Raspberry > Pis. > > Signed-off-by: Zygo Blaxell <ce3g8jdj@xxxxxxxxxxxxxxxxxxxxx> > --- > fs/btrfs/volumes.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c > index 88a323a453d8..252c6049c6b7 100644 > --- a/fs/btrfs/volumes.c > +++ b/fs/btrfs/volumes.c > @@ -3906,7 +3906,11 @@ static int alloc_profile_is_valid(u64 flags, int extended) > return !extended; /* "0" is valid for usual profiles */ > > /* true if exactly one bit set */ > - return is_power_of_2(flags); > + /* > + * Don't use is_power_of_2(unsigned long) because it won't work > + * for the single profile (1ULL << 48) on 32-bit CPUs. > + */ > + return flags != 0 && (flags & (flags - 1)) == 0; I'd rather not open code it again. Based on the discussion, we need a separate helper that takes u64 and possibly has the "value has exactly one bit set" semantics from the beginnin. We now have a file for such helpers (fs/btrfs/misc.h). There would a few more users of the new helper (now done using the is_power_of_2 helper), that would improve readability.
