Re: shared memory mechanism other than ivshmem

[Sanjeev Kumar]

and there is this missing part in patches in  https://lore.kernel.org/qemu-devel/20240222222218.2261956-1-gustavo.romero@linaro.org/

 missing property for ivshmem-flat "x-bus-qompath" which is present in 

https://lore.kernel.org/qemu-devel/20231127052024.435743-2-gustavo.romero@linaro.org/

patches.

without that prop, 

-chardev socket,path=/tmp/ivshmem_socket,id=ivshmem_flat -device ivshmem-flat,chardev=ivshmem_flat,x-irq-qompath='/machine/unattached/device[4]/gic/unnamed-gpio-in[0]',x-bus-qompath='/sysbus'

isn't working.

On Thu, May 16, 2024 at 2:52 PM Sanjeev Kumar <reachsanjeev7@gmail.com> wrote:

Hi Philippe,

I have taken patches from the link you provided

and built QEMU and started appending below line to QEMU

-chardev socket,path=/tmp/ivshmem_socket,id=ivshmem_flat -device ivshmem-flat,chardev=ivshmem_flat,x-irq-qompath='/machine/unattached/device[4]/gic/unnamed-gpio-in[0]',x-bus-qompath='/sysbus'

and QEMU boots without any error

I would like to get some help regarding data writing and reading from shared memory.

when using ivshmem-plain, i used to write data from host like 

echo "hello" > /dev/shm/shm1 and in guest i was reading from pci bus BAR and i was able to get data.

similarly can you please help me with ivshmem-flat like where is the location to write/read the data from host and in guest.

Thanks & Regards,

Sanjeev.

On Tue, May 14, 2024 at 9:56 PM Philippe Mathieu-Daudé <philmd@linaro.org> wrote:

On 14/5/24 12:23, Sanjeev Kumar wrote:
> and forgot to mention. why our VM doesn't support ivshmem because it
> doesn't have PCI supported.
> Is there any other shared memory mechanism QEMU which doesn't use the
> PCI interface?
>
> On Tue, May 14, 2024 at 11:28 AM Sanjeev Kumar <reachsanjeev7@gmail.com
> <mailto:reachsanjeev7@gmail.com>> wrote:
>
>     Hi,
>     is there any other mechanism of shared memory with QEMU other than
>     ivshmem?
>     I tried ivshmem with ubuntu vm with qemu x86_64 and it is working
>     fine. but our use case is with ARM and ivshmem isn't supported by
>     our custom VM. so please let me know if we have any other mechanism
>     other than ivshmem.

Hi Sanjeev,

You might be interested by Gustavo approach (he provided some
examples):
https://lore.kernel.org/qemu-devel/20240222222218.2261956-1-gustavo.romero@linaro.org/

Regards,

Phil.