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Re: [Qemu-devel] [PATCH] hw/arm/virt: explain device-to-transport mappin
Re: [Qemu-devel] [PATCH] hw/arm/virt: explain device-to-transport mapping in create_virtio_devices()
Tue, 3 Feb 2015 11:51:16 +0000
On 30 January 2015 at 04:34, Laszlo Ersek <address@hidden> wrote:
> On 01/30/15 05:31, Laszlo Ersek wrote:
>> Signed-off-by: Laszlo Ersek <address@hidden>
>> hw/arm/virt.c | 32 ++++++++++++++++++++++++++++----
>> 1 file changed, 28 insertions(+), 4 deletions(-)
>> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
>> index 2353440..091e5ee 100644
>> --- a/hw/arm/virt.c
>> +++ b/hw/arm/virt.c
>> @@ -441,10 +441,27 @@ static void create_virtio_devices(const VirtBoardInfo
>> *vbi, qemu_irq *pic)
>> int i;
>> hwaddr size = vbi->memmap[VIRT_MMIO].size;
>> - /* Note that we have to create the transports in forwards order
>> - * so that command line devices are inserted lowest address first,
>> - * and then add dtb nodes in reverse order so that they appear in
>> - * the finished device tree lowest address first.
>> + /* We create the transports in forwards order. Since qbus_realize()
>> + * prepends (not appends) new child buses, the incrementing loop below
>> + * create a list of virtio-mmio buses with decreasing base addresses.
>> + *
>> + * When a -device option is processed from the command line,
>> + * qbus_find_recursive() picks the next free virtio-mmio bus in forwards
>> + * order. The upshot is that -device options in increasing command line
>> + * order are mapped to virtio-mmio buses with decreasing base addresses.
>> + *
>> + * When this code was originally written, that arrangement ensured that
>> + * guest Linux kernel would give the lowest "name" (/dev/vda, eth0,
>> etc) to
>> + * the first -device on the command line. (The end-to-end order is a
>> + * function of this loop, qbus_realize(), qbus_find_recursive(), and the
>> + * guest kernel's name-to-address assignment strategy.)
>> + *
>> + * Meanwhile, the kernel's traversal seems to have been reserved; see
> can you please s/reserved/reversed/?
> Result of over-editing, sorry.
Sure, no problem. I also suggest I add this para:
* In any case, the kernel makes no guarantee about the stability of
* enumeration order of virtio devices (as demonstrated by it changing
* between kernel versions). For reliable and stable identification
* of disks users must use UUIDs or similar mechanisms.
- Re: [Qemu-devel] [PATCH] hw/arm/virt: explain device-to-transport mapping in create_virtio_devices(),
Peter Maydell <=