Re: [Qemu-devel] [PATCH v4 00/21] nbd: add qemu-nbd --list

[Richard W.M. Jones]

On Fri, Jan 18, 2019 at 04:47:42PM -0600, Eric Blake wrote:
> It matches the code, but I just learned the code is buggy for anything
> larger than 5.  According to
> http://tldp.org/HOWTO/Large-Disk-HOWTO-13.html, MBR Extended/Logical
> partitions form a linked-list, something like:
> 
> MBR:              EBR1              EBR2
> +----------+      +----------+      +----------+
> + Part 1   +   |->+ Part 5   +   |->+ Part 6   +
> + Part 2   +   |  + Next --------|  + 0        +
> + Part 3   +   |  + 0        +      + 0        +
> + Part 4 -------  + 0        +      + 0        +
> +----------+      +----------+      +----------+

Wikipedia's description is a bit better:

https://en.wikipedia.org/wiki/Extended_boot_record

In fact it's not strictly a linked list because the start record of
each entry is relative to the extended partition start.  It's all a
bit weird.

But you're right, nbdkit can neither read (nbdkit-partition-filter)
nor write (nbdkit-partitioning-plugin) MBR logical partitions so we
can't test interop or tell people to use nbdkit for this corner case.

Rich.

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