On Thu, Aug 25, 2011 at 3:02 PM, Pekka Enberg <penberg@xxxxxxxxxx> wrote: > On 8/25/11 9:30 AM, Asias He wrote: >> >> On Thu, Aug 25, 2011 at 1:54 PM, Pekka Enberg<penberg@xxxxxxxxxx> wrote: >>> >>> On 8/25/11 8:34 AM, Asias He wrote: >>> >>> Hi, David >>> >>> On Thu, Aug 25, 2011 at 6:25 AM, David Evensky<evensky@xxxxxxxxxx> >>> wrote: >>>> >>>> This patch adds a PCI device that provides PCI device memory to the >>>> guest. This memory in the guest exists as a shared memory segment in >>>> the host. This is similar memory sharing capability of Nahanni >>>> (ivshmem) available in QEMU. In this case, the shared memory segment >>>> is exposed as a PCI BAR only. >>>> >>>> A new command line argument is added as: >>>> --shmem pci:0xc8000000:16MB:handle=/newmem:create >>>> >>>> which will set the PCI BAR at 0xc8000000, the shared memory segment >>>> and the region pointed to by the BAR will be 16MB. On the host side >>>> the shm_open handle will be '/newmem', and the kvm tool will create >>>> the shared segment, set its size, and initialize it. If the size, >>>> handle, or create flag are absent, they will default to 16MB, >>>> handle=/kvm_shmem, and create will be false. >>> >>> I think it's better to use a default BAR address if user does not specify >>> one as well. >>> This way, >>> >>> ./kvm --shmem >>> >>> will work with default values with zero configuration. >>> >>> Does that sort of thing make sense here? It's a special purpose device >>> and the guest is expected to ioremap() the memory so it needs to >>> know the BAR. >> >> I mean a default bar address for --shmem device. Yes, guest needs to know >> this address, but even if we specify the address at command line the guest >> still >> does not know this address, no? So having a default bar address does no >> harm. > > How does the user discover what the default BAR is? Which default BAR > should we use? I don't think default BAR adds much value here. 1. Print it on startup like, like we do for --name. # kvm run -k ./bzImage -m 448 -c 4 --name guest-26676 --shmem bar=0xc8000000 or 2. kvm stat --shmem David has chosen a default BAR already. #define SHMEM_DEFAULT_ADDR (0xc8000000) >>>> The address family, >>>> 'pci:' is also optional as it is the only address family currently >>>> supported. Only a single --shmem is supported at this time. >>> >>> So, let's drop the 'pci:' prefix. >>> >>> That means the user interface will change if someone adds new address >>> families. So we should keep the prefix, no? >> >> We can have a more flexible option format which does not depend on the >> order of >> args, e.g.: >> >> --shmem bar=0xc8000000,size=16MB,handle=/newmem,ops=create, type=pci >> >> if user does not specify sub-args, just use the default one. > > Sure, makes sense. > > Pekka > -- Asias He -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
