[PATCH] xfs: introduce "metasync" api to sync metadata to fsblock

[Christoph Hellwig]

On Sun, Oct 13, 2019 at 10:37:00PM +0800, Pingfan Liu wrote:
> When using fadump (fireware assist dump) mode on powerpc, a mismatch
> between grub xfs driver and kernel xfs driver has been obsevered.  Note:
> fadump boots up in the following sequence: fireware -> grub reads kernel
> and initramfs -> kernel boots.

This isn't something new.  To fundamentally fix this you need to
implement (in-memory) log recovery in grub.  That is the only really safe
long-term solutioin.  But the equivalent of your patch you can already
get by freezing and unfreezing the file system using the FIFREEZE and
FITHAW ioctls.  And if my memory is serving me correctly Dave has been
preaching that to the bootloader folks for a long time, but apparently
without visible results.