On 02/03/15 12:51, Peter Maydell wrote: > On 30 January 2015 at 04:34, Laszlo Ersek <ler...@redhat.com> wrote: >> Peter, >> >> On 01/30/15 05:31, Laszlo Ersek wrote: >>> Signed-off-by: Laszlo Ersek <ler...@redhat.com> >>> --- >>> 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 >>> will >>> + * 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 the >>> + * 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 >>> eg. >> >> 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.
Thanks. Do you want me to resubmit, or can you just squash it and observe that fact in a [peter.mayd...@linaro.org: note about UUIDs] betwixt two other tags? Thanks Laszlo PS: yes, I love "betwixt". Whether I used it correctly above is secondary. ;)
