linux-kernel - Re: [PATCH v5] mm/hmm/test: use char dev with struct device to get device node

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Date:   Fri, 25 Mar 2022 15:17:39 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     mpenttil@...hat.com
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        apopple@...dia.com, jhubbard@...dia.com, rcampbell@...dia.com,
        vbabka@...e.cz
Subject: Re: [PATCH v5] mm/hmm/test: use char dev with struct device to get
 device node

On Tue, Mar 22, 2022 at 06:35:43AM +0200, mpenttil@...hat.com wrote:
> From: Mika Penttilä <mpenttil@...hat.com>
> 
> HMM selftests use an in-kernel pseudo device to emulate device private
> memory. The pseudo device registers a major device range for two pseudo
> device instances. User space has a script that reads /proc/devices in
> order to find the assigned major number, and sends that to mknod(1),
> once for each node.
> 
> Change this to properly use cdev and struct device APIs.
> 
> Delete the /proc/devices parsing from the user-space test script, now
> that it is unnecessary.
> 
> Also, deleted an unused field in struct dmirror_device: devmem.
> 
> Signed-off-by: Mika Penttilä <mpenttil@...hat.com>
> Reviewed-by: John Hubbard <jhubbard@...dia.com>
> Cc: Alistair Popple <apopple@...dia.com>
> Cc: Ralph Campbell <rcampbell@...dia.com>
> Cc: Jason Gunthorpe <jgg@...pe.ca>
> Cc: Vlastimil Babka <vbabka@...e.cz>
> v5:
>         - fix whitespace
>         . delete unused structure field     
> v4:
>         - fix commit log
> v3:
>         - use cdev_device_add() instead of miscdevice
> v2:
>         - Cleanups per review comments from John Hubbard
>         - Added Tested-by and Ccs
> 
>  lib/test_hmm.c                         | 18 ++++++++++++++----
>  tools/testing/selftests/vm/test_hmm.sh |  6 ------
>  2 files changed, 14 insertions(+), 10 deletions(-)
> 
> diff --git a/lib/test_hmm.c b/lib/test_hmm.c
> index 767538089a62..3c7f2a92b09e 100644
> +++ b/lib/test_hmm.c
> @@ -29,11 +29,17 @@
>  
>  #include "test_hmm_uapi.h"
>  
> -#define DMIRROR_NDEVICES		2
>  #define DMIRROR_RANGE_FAULT_TIMEOUT	1000
>  #define DEVMEM_CHUNK_SIZE		(256 * 1024 * 1024U)
>  #define DEVMEM_CHUNKS_RESERVE		16
>  
> +static const char *dmirror_device_names[] = {
> +	"hmm_dmirror0",
> +	"hmm_dmirror1"
> +};
> +
> +#define DMIRROR_NDEVICES ARRAY_SIZE(dmirror_device_names)
> +
>  static const struct dev_pagemap_ops dmirror_devmem_ops;
>  static const struct mmu_interval_notifier_ops dmirror_min_ops;
>  static dev_t dmirror_dev;
> @@ -83,7 +89,7 @@ struct dmirror_chunk {
>   */
>  struct dmirror_device {
>  	struct cdev		cdevice;
> -	struct hmm_devmem	*devmem;
> +	struct device		device;
>  
>  	unsigned int		devmem_capacity;
>  	unsigned int		devmem_count;
> @@ -1225,7 +1231,11 @@ static int dmirror_device_init(struct dmirror_device *mdevice, int id)
>  
>  	cdev_init(&mdevice->cdevice, &dmirror_fops);
>  	mdevice->cdevice.owner = THIS_MODULE;
> -	ret = cdev_add(&mdevice->cdevice, dev, 1);
> +	device_initialize(&mdevice->device);
> +	dev_set_name(&mdevice->device, "%s", dmirror_device_names[id]);

Just 
	dev_set_name(&mdevice->device, "hmm_dmirror%u", id);

No need for an array

Also check for error

Jason