linux-kernel - Re: [PATCH] ocxl: Add get_metadata IOCTL to share OCXL information to userspace

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Date:   Wed, 21 Feb 2018 17:43:59 +1100
From:   Balbir Singh <bsingharora@...il.com>
To:     "Alastair D'Silva" <alastair@....ibm.com>
Cc:     linuxppc-dev <linuxppc-dev@...abs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>, frederic.barrat@...ibm.com,
        Greg KH <gregkh@...uxfoundation.org>,
        Andrew Donnellan <andrew.donnellan@....ibm.com>,
        "Alastair D'Silva" <alastair@...ilva.org>
Subject: Re: [PATCH] ocxl: Add get_metadata IOCTL to share OCXL information to userspace

On Wed, Feb 21, 2018 at 3:57 PM, Alastair D'Silva <alastair@....ibm.com> wrote:
> From: Alastair D'Silva <alastair@...ilva.org>
>
> Some required information is not exposed to userspace currently (eg. the
> PASID), pass this information back, along with other information which
> is currently communicated via sysfs, which saves some parsing effort in
> userspace.
>
> Signed-off-by: Alastair D'Silva <alastair@...ilva.org>
> ---
>  drivers/misc/ocxl/file.c | 27 +++++++++++++++++++++++++++
>  include/uapi/misc/ocxl.h | 22 ++++++++++++++++++++++
>  2 files changed, 49 insertions(+)
>
> diff --git a/drivers/misc/ocxl/file.c b/drivers/misc/ocxl/file.c
> index d9aa407db06a..11514a8444e5 100644
> --- a/drivers/misc/ocxl/file.c
> +++ b/drivers/misc/ocxl/file.c
> @@ -102,10 +102,32 @@ static long afu_ioctl_attach(struct ocxl_context *ctx,
>         return rc;
>  }
>
> +static long afu_ioctl_get_metadata(struct ocxl_context *ctx,
> +               struct ocxl_ioctl_get_metadata __user *uarg)

Why do we call this metadata? Isn't this an afu_descriptor?

> +{
> +       struct ocxl_ioctl_get_metadata arg;
> +
> +       memset(&arg, 0, sizeof(arg));
> +
> +       arg.version = 0;

Does it make sense to have version 0? Even if does, you can afford
to skip initialization due to the memset above. I prefer that versions
start with 1

> +
> +       arg.afu_version_major = ctx->afu->config.version_major;
> +       arg.afu_version_minor = ctx->afu->config.version_minor;
> +       arg.pasid = ctx->pasid;
> +       arg.pp_mmio_size = ctx->afu->config.pp_mmio_stride;
> +       arg.global_mmio_size = ctx->afu->config.global_mmio_size;
> +
> +       if (copy_to_user(uarg, &arg, sizeof(arg)))
> +               return -EFAULT;
> +
> +       return 0;
> +}
> +
>  #define CMD_STR(x) (x == OCXL_IOCTL_ATTACH ? "ATTACH" :                        \
>                         x == OCXL_IOCTL_IRQ_ALLOC ? "IRQ_ALLOC" :       \
>                         x == OCXL_IOCTL_IRQ_FREE ? "IRQ_FREE" :         \
>                         x == OCXL_IOCTL_IRQ_SET_FD ? "IRQ_SET_FD" :     \
> +                       x == OCXL_IOCTL_GET_METADATA ? "GET_METADATA" : \
>                         "UNKNOWN")
>
>  static long afu_ioctl(struct file *file, unsigned int cmd,
> @@ -157,6 +179,11 @@ static long afu_ioctl(struct file *file, unsigned int cmd,
>                                         irq_fd.eventfd);
>                 break;
>
> +       case OCXL_IOCTL_GET_METADATA:
> +               rc = afu_ioctl_get_metadata(ctx,
> +                               (struct ocxl_ioctl_get_metadata __user *) args);
> +               break;
> +
>         default:
>                 rc = -EINVAL;
>         }
> diff --git a/include/uapi/misc/ocxl.h b/include/uapi/misc/ocxl.h
> index 4b0b0b756f3e..16e1f48ce280 100644
> --- a/include/uapi/misc/ocxl.h
> +++ b/include/uapi/misc/ocxl.h
> @@ -32,6 +32,27 @@ struct ocxl_ioctl_attach {
>         __u64 reserved3;
>  };
>
> +/*
> + * Version contains the version of the struct.
> + * Versions will always be backwards compatible, that is, new versions will not
> + * alter existing fields
> + */
> +struct ocxl_ioctl_get_metadata {

This sounds more like a function name, do we need it to be _get_metdata?

> +       __u16 version;
> +
> +       // Version 0 fields
> +       __u8  afu_version_major;
> +       __u8  afu_version_minor;
> +       __u32 pasid;
> +
> +       __u64 pp_mmio_size;
> +       __u64 global_mmio_size;
> +

Should we document the fields? pp_ stands for per process, but is not
very clear at first look. Why do we care to return only the size, what
about lpc size?

> +       // End version 0 fields
> +
> +       __u64 reserved[13]; // Total of 16*u64
> +};


Balbir Singh.