On Tue 2017-07-25 00:51:56, Theodore Ts'o wrote:

On Mon, Jul 24, 2017 at 10:04:51PM +0200, Pavel Machek wrote:

quoted

Question for you was... Is the first 1KiB of each ext4 filesystem still
free and "reserved for a bootloader"?

Yes.

Thanks.

quoted

If I needed more for bcache superblock (8KiB, IIRC), would that be
easy to accomplish on existing filesystem?

Huh?  Why would the bcache superblock matter when you're talking about
the ext4 layout?  The bcache superblock will be on the bcache
device/partition, and the ext4 superblock will be on the ext4
device/partition.

I'd like to enable bcache on already existing ext4 partition. AFAICT
normal situation, even on the backing device, is:

| 8KiB bcache superblock | 1KiB reserved | ext4 superblock | 400GB data |

Unfortunately, that would mean shifting 400GB data 8KB forward, and
compatibility problems. So I'd prefer adding bcache superblock into
the reserved space, so I can have caching _and_ compatibility with
grub2 etc (and avoid 400GB move):

| 1KiB (modified) bcache superblock | ext4 superblock | 400GB data |

Best regards,
									Pavel
-- 
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