Re: [ndctl PATCH v3 04/21] libcxl: add support for command query and submission

From: "Verma, Vishal L" <vishal.l.verma@intel.com>
To: "Williams, Dan J" <dan.j.williams@intel.com>
Cc: "Widawsky, Ben" <ben.widawsky@intel.com>,
	"linux-cxl@vger.kernel.org" <linux-cxl@vger.kernel.org>,
	"nvdimm@lists.linux.dev" <nvdimm@lists.linux.dev>,
	"Schofield, Alison" <alison.schofield@intel.com>,
	"Weiny, Ira" <ira.weiny@intel.com>
Subject: Re: [ndctl PATCH v3 04/21] libcxl: add support for command query and submission
Date: Tue, 13 Jul 2021 21:17:32 +0000	[thread overview]
Message-ID: <14151c2efffe947103b881da5bbf38212786aa59.camel@intel.com> (raw)
In-Reply-To: <CAPcyv4iyhpSYkDKYDjWP61PaahtZrn3pGh7NnfC6jDaNbVEu+w@mail.gmail.com>

On Mon, 2021-07-12 at 22:12 -0700, Dan Williams wrote:
> On Thu, Jul 1, 2021 at 1:10 PM Vishal Verma <vishal.l.verma@intel.com> wrote:
> > 
> > Add a set of APIs around 'cxl_cmd' for querying the kernel for supported
> > commands, allocating and validating command structures against the
> > supported set, and submitting the commands.
> > 
> > 'Query Commands' and 'Send Command' are implemented as IOCTLs in the
> > kernel. 'Query Commands' returns information about each supported
> > command, such as flags governing its use, or input and output payload
> > sizes. This information is used to validate command support, as well as
> > set up input and output buffers for command submission.
> 
> It strikes me after reading the above that it would be useful to have
> a cxl list option that enumerates the command support on a given
> memdev. Basically a "query-to-json" helper.

Hm, yes that makes sense..  There may not always be a 1:1 correlation
between the commands returned by query and the actual cxl-cli command
corresponding with that - and for some commands, there may not even be
a cxl-cli equivalent. Do we want to create a json representation of the
raw query data, or cxl-cli equivalents?

> > 
> > Cc: Ben Widawsky <ben.widawsky@intel.com>
> > Cc: Dan Williams <dan.j.williams@intel.com>
> > Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
> > ---
> >  cxl/lib/private.h  |  33 ++++
> >  cxl/lib/libcxl.c   | 388 +++++++++++++++++++++++++++++++++++++++++++++
> >  cxl/libcxl.h       |  11 ++
> >  cxl/lib/libcxl.sym |  13 ++
> >  4 files changed, 445 insertions(+)
> > 
> [..]
> > +static int cxl_cmd_alloc_query(struct cxl_cmd *cmd, int num_cmds)
> > +{
> > +       size_t size;
> > +
> > +       if (!cmd)
> > +               return -EINVAL;
> > +
> > +       if (cmd->query_cmd != NULL)
> > +               free(cmd->query_cmd);
> > +
> > +       size = sizeof(struct cxl_mem_query_commands) +
> > +                       (num_cmds * sizeof(struct cxl_command_info));
> 
> This is asking for the kernel's include/linux/overflow.h to be
> imported into ndctl so that struct_size() could be used here. The file
> is MIT licensed, just the small matter of factoring out only the MIT
> licensed bits.

Ah ok let me take a look.

> Other than that, looks good to me.