linux-kernel - Re: [PATCH] drivers/scsi/emcctd: drivers/scsi/emcctd: Client driver implementation for EMC-Symmetrix GuestOS emulated Cut-Through Device

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Date:	Tue, 19 Jan 2016 10:12:26 -0800
From:	Greg KH <greg@...ah.com>
To:	"Singhal, Maneesh" <Maneesh.Singhal@....com>
Cc:	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"JBottomley@...n.com" <JBottomley@...n.com>,
	"martin.petersen@...cle.com" <martin.petersen@...cle.com>,
	"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>
Subject: Re: [PATCH] drivers/scsi/emcctd: drivers/scsi/emcctd: Client driver
 implementation for  EMC-Symmetrix GuestOS emulated Cut-Through Device

On Tue, Jan 19, 2016 at 11:58:06AM +0000, Singhal, Maneesh wrote:
> Hello,
> Kindly review the following patch for the following driver to be added in SCSI subsystem -
> 
> Regards
> Maneesh
> 
> ----------------------------------------------------------------------------
> >From f3c4b836d6f130b1d7ded618002c8164f8f4a06d Mon Sep 17 00:00:00 2001
> From: "maneesh.singhal" <maneesh.singhal@....com>
> Date: Tue, 19 Jan 2016 06:39:35 -0500
> Subject: [PATCH] [PATCH] drivers/scsi/emcctd: Client driver implementation for
>  EMC-Symmetrix GuestOS emulated Cut-Through Device.
> 
> The patch is a driver implementation  EMC-Symmetrix GuestOS emulated Cut-Through
> Device. The Cut-Through Device PCI emulation is implemented for GuestOS
> environments in the HyperMax OS. GuestOS environments allows loading of
> any x86 compliant operating systems like Linux/FreeBSD etc.
> 
> The client driver is a SCSI HBA implementation which interfaces with SCSI
> midlayer in the north-bound interfaces and connects with the emulated PCI device
> on the south side.
> 
> The PCI vendor ID:product ID for emulated Cut-Through Device is 0x1120:0x1B00.
> 
> Signed-off-by: maneesh.singhal <maneesh.singhal@....com>
> ---
>  Documentation/scsi/emcctd.txt           |   57 +
>  MAINTAINERS                             |    9 +
>  drivers/scsi/Kconfig                    |    1 +
>  drivers/scsi/Makefile                   |    1 +
>  drivers/scsi/emcctd/Kconfig             |    7 +
>  drivers/scsi/emcctd/Makefile            |    1 +
>  drivers/scsi/emcctd/README              |   10 +
>  drivers/scsi/emcctd/emc_ctd_interface.h |  386 +++++
>  drivers/scsi/emcctd/emcctd.c            | 2840 +++++++++++++++++++++++++++++++
>  drivers/scsi/emcctd/emcctd.h            |  232 +++
>  10 files changed, 3544 insertions(+)
>  create mode 100644 Documentation/scsi/emcctd.txt
>  create mode 100644 drivers/scsi/emcctd/Kconfig
>  create mode 100644 drivers/scsi/emcctd/Makefile
>  create mode 100644 drivers/scsi/emcctd/README
>  create mode 100644 drivers/scsi/emcctd/emc_ctd_interface.h
>  create mode 100644 drivers/scsi/emcctd/emcctd.c
>  create mode 100644 drivers/scsi/emcctd/emcctd.h
> 
> diff --git a/Documentation/scsi/emcctd.txt b/Documentation/scsi/emcctd.txt
> new file mode 100644
> index 0000000..bcafc87
> --- /dev/null
> +++ b/Documentation/scsi/emcctd.txt
> @@ -0,0 +1,56 @@
> +This file contains brief information about the EMC Cut-Through Driver (emcctd).
> +The driver is currently maintained by Singhal, Maneesh (maneesh.singhal@....com)
> +
> +Last modified: Mon Jan 18 2016 by Maneesh Singhal
> +
> +BASICS
> +
> +Its a client driver implementation for EMC-Symmetrix GuestOS emulated
> +Cut-Through Device. The Cut-Through Device PCI emulation is implemented for
> +GuestOS environments in the HyperMax OS. GuestOS environments allows loading of
> +any x86 compliant operating systems like Linux/FreeBSD etc.
> +
> +The client driver is a SCSI HBA implementation which interfaces with SCSI
> +midlayer in the north-bound interfaces and connects with the emulated PCI device
> +on the south side.
> +
> +The PCI vendor ID:product ID for emulated Cut-Through Device is 0x1120:0x1B00.
> +
> +VERSIONING
> +
> +The Version of the driver is maintained as 2.0.0.X, where 2 refers to the CTD
> +protocol in use, and X refers to the ongoing version of the driver.
> +
> +
> +SYSFS SUPPORT
> +
> +The driver creates the directory /sys/module/emcctd and populates it with
> +version file and a directory for various parameters as described in MODULE
> +PARAMETERS section.
> +
> +PROCFS SUPPORT
> +
> +The driver creates the directory /proc/emc and creates files emcctd_stats_x
> +where 'x' refers to the PCI emulation number this client driver connected to.
> +These files cotains WWN information and IO statistics for the particular PCI
> +emulation.

No, no driver should be adding proc files, please use sysfs or debugfs
for debugging things.

> +MODULE PARAMETERS

No driver should be using module parameters anymore, again, please use
the correct interfaces.

> +
> +The supported parameters which could add debuggability or change the runtime
> +behavior of the driver are as following:
> +
> +ctd_debug=0 | 1		Enable driver debug messages(0=off, 1=on)

Use the dynamic debugging interface, don't make a custom one just for
your tiny, single, driver.

> +
> +max_luns=xx		Specify the maximum number of LUN's per
> +			host(default=16384)

Why can't this be dynamic?  Why do you need a static number?

> +
> +cmd_per_lun=xx		Specify the maximum commands per lun(default=16)

Why do you need to change this?  Why can't it be dynamic?

> +
> +DEBUGGING HINTS
> +
> +Debugging code is now compiled in by default but debugging is turned off
> +with the kernel module parameter debug_flag defaulting to 0.

Again, no, use the dynamic debug interface, don't make something
"special" just for a single driver, we spent a lot of time trying to
unify everything, don't go backwards.

thanks,

greg k-h