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由 David Gibson 提交于
The PAPR specification defines a virtual TTY/console interface for guest OSes to use via the H_PUT_TERM_CHAR and H_GET_TERM_CHAR hypercalls. There can be multiple virtual ttys, so these take a "termno" parameter. This encodes which vty to use as the 'reg' property on the device tree node associated with that vty. However, with the early debug options enabled, the Linux kernel will attempt debugging output through the vty very early, before it has read the device tree. In this case it always uses a termno of 0. This works on the existing PowerVM hypervisor, so we assume there must be a hack / feature in there which interprets termno==0 to mean the default primary console. To help with debugging kernels, including existing distribution kernels, this patch implements a similar feature / hack in qemu. If termno==0 is supplied to H_{GET,PUT}_TERM_CHAR, they use the first available vty device instead. We need to be careful in the case that the user has manually created an spapr-vty at address 0. So first we search for the specified reg and only if that doesn't match do we fall back. Signed-off-by: NMichael Ellerman <michael@ellerman.id.au> Signed-off-by: NDavid Gibson <david@gibson.dropbear.id.au> Signed-off-by: NAlexander Graf <agraf@suse.de>
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