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

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Message-Id: <c6017f9f-67f0-10eb-1eed-527c9c5298ba@linux.vnet.ibm.com>
Date:   Wed, 21 Feb 2018 12:25:42 +0100
From:   Frederic Barrat <fbarrat@...ux.vnet.ibm.com>
To:     Balbir Singh <bsingharora@...il.com>,
        "Alastair D'Silva" <alastair@....ibm.com>
Cc:     Arnd Bergmann <arnd@...db.de>, frederic.barrat@...ibm.com,
        Greg KH <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...abs.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



Le 21/02/2018 à 07:43, Balbir Singh a écrit :
> 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?

My bad, I forgot to mention it before. There's a somewhat high-level 
description which needs updating in:
Documentation/accelerators/ocxl.rst

It doesn't go down to the level of the structure members, but at least 
all ioctl commands should have a brief description.

lpc_size could be added. It's currently useless to the library, but 
doesn't hurt. The one which was giving me troubles on a previous version 
of this patch was the lpc numa node ID, since that was experimental code 
and felt out of place considering what's been upstreamed in skiboot and 
linux so far.

   Fred


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