[libvirt] [PATCH v4 1/2] qemu_domain: NVLink2 bridge detection function for PPC64

[Peter Krempa]

On Tue, Mar 12, 2019 at 18:55:49 -0300, Daniel Henrique Barboza wrote:
> The NVLink2 support in QEMU implements the detection of NVLink2
> capable devices by verifying the attributes of the VFIO mem region
> QEMU allocates for the NVIDIA GPUs. To properly allocate an
> adequate amount of memLock, Libvirt needs this information before
> a QEMU instance is even created, thus querying QEMU is not
> possible and opening a VFIO window is too much.
> 
> An alternative is presented in this patch. Making the following
> assumptions:
> 
> - if we want GPU RAM to be available in the guest, an NVLink2 bridge
> must be passed through;
> 
> - an unknown PCI device can be classified as a NVLink2 bridge
> if its device tree node has 'ibm,gpu', 'ibm,nvlink',
> 'ibm,nvlink-speed' and 'memory-region'.
> 
> This patch introduces a helper called @ppc64VFIODeviceIsNV2Bridge
> that checks the device tree node of a given PCI device and
> check if it meets the criteria to be a NVLink2 bridge. This
> new function will be used in a follow-up patch that, using the
> first assumption, will set up the rlimits of the guest
> accordingly.
> 
> Signed-off-by: Daniel Henrique Barboza <danielhb413 at gmail.com>
> ---
>  src/qemu/qemu_domain.c | 29 +++++++++++++++++++++++++++++
>  1 file changed, 29 insertions(+)

disclaimer: This is a code review. I don't have much knowledge about
what you are trying to implement.


> 
> diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
> index 1659e88478..dcc92d253c 100644
> --- a/src/qemu/qemu_domain.c
> +++ b/src/qemu/qemu_domain.c
> @@ -10398,6 +10398,35 @@ qemuDomainUpdateCurrentMemorySize(virDomainObjPtr vm)
>  }
>  
>  
> +/**
> + * ppc64VFIODeviceIsNV2Bridge:
> + * @device: string with the PCI device address
> + *
> + * This function receives a string that represents a PCI device,
> + * such as '0004:04:00.0', and tells if the device is a NVLink2
> + * bridge.
> + */
> +static bool
> +ppc64VFIODeviceIsNV2Bridge(const char *device)
> +{
> +    const char *nvlink2Files[] = {"ibm,gpu", "ibm,nvlink",
> +                                  "ibm,nvlink-speed", "memory-region"};
> +    char *file;
> +    size_t i;
> +
> +    for (i = 0; i < 4; i++) {

Use ARRAY_CARDINALITY(nvlink2Files) instead of '4'.

> +        if ((virAsprintf(&file, "/sys/bus/pci/devices/%s/of_node/%s",
> +                         device, nvlink2Files[i])) < 0)
> +            return false;
> +
> +        if (!virFileExists(file))
> +            return false;

memory allocated to 'file' is leaked in every loop and also at exit. You
can use VIR_AUTOFREE(char *) file above, but you need to free the
pointer also in every single loop.

> +    }
> +
> +    return true;
> +}

This function is unused and static, this means the build will fail after
this patch.

> +
> +
>  /**
>   * getPPC64MemLockLimitBytes:
>   * @def: domain definition
> -- 
> 2.20.1
> 
> --
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> libvir-list at redhat.com
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