Re: [RFC] make btrfs-image work

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On Wed, Jan 20, 2010 at 12:04 AM, Josef Bacik <josef@xxxxxxxxxx> wrote:
> Hello,
>
> btrfs-image would be very helpful for debugging some users problems that we
> can't reproduce ourselves, but every image that i try and re-create with
> btrfs-image makes btrfs panic.  This is because we zero out the superblocks
> chunk array and re-create our uuid.  This means that we end up not being able to
> read the chunk tree on mount, and then even if we could the uuid's of the
> metadata we read back wouldn't match the uuid of the device.  The way I've fixed
> this is to just spit the metadata back onto the disk exactly the way we got it.
> The caveat to this I think is that if we try to image a multi-device setup that
> it won't work right unless we have a multi-device setup to restore the image
> onto.  I'm not sure if thats the goal or not.  This patch makes the single disk
> case work fine for me.  Let me know what you think.  Thanks,
>

The goal of btrfs-image is create image that can be  examined by btrfsck and
btrfs-debug-tree. btrfs-image creates metadata image for btrfs' logical address
space. So your patch only works for the uncommon case that btrfs' logical
address is mapped to offset of device.

Yan, Zheng
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