Re: [Qemu-devel] [PATCH REPOST] fw_cfg: Allow guest to read kernel etc via fast, synchronous "DMA"-type operation.

[Paul Brook]

> I rebased this and rechecked it.  The *total* libguestfs boot time
> goes from 86 seconds down to 7.7 seconds.  The proportion of that
> attributable to loading the appliance is approximately 650 times [sic]
> faster.

Nack.

> +/* Target address and size for DMA operations.  This is only used
> + * during boot and across 32 and 64 bit architectures, so only writes
> + * to lower 4GB addresses are supported.
> + */
> +static uint32_t dma_addr = 0;
> +static uint32_t dma_size = 0;

Storing per-device state in global variables is just plain wrong.
Limiting addresses to 32-bits is just lame. You can do better.
It's also completely broken on big-endian hosts.

Paul