On 18/09/2018 19.15, Goffredo Baroncelli wrote:

quoted

b. The bootloader code, would have to have sophisticated enough Btrfs
knowledge to know if the grubenv has been reflinked or snapshot,
because even if +C, it may not be valid to overwrite, and COW must
still happen, and there's no way the code in GRUB can do full blow COW
and update a bunch of metadata.

And what if GRUB ignore the possibility of COWing and overwrite the data ? Is it a so big problem that the data is changed in all the snapshots ? 
It would be interested if the same problem happens for a swap file.....

I gave a look to the Sandoval's patches about implementing swap on BTRFS. This patch set
prevents the subvolume containing the swapfile to be snapshot-ted (and the file to be balanced and so on...); what if we would add the same constraint to the grubenv file ?


BR
G.Baroncelli
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