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

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Date:   Sat, 26 Mar 2022 05:19:55 +0200
From:   Mika Penttilä <mpenttil@...hat.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
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 25.3.2022 20.17, Jason Gunthorpe wrote:
> 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

Yeah, no absolute need, thought names in an array is less hardcoded wrt 
device node count and naming standard.

> 
> Also check for error

True. Interesting fact is that even the device core itself doesn't check 
for errors calling dev_set_name(), but sure it can fail in memory 
allocations.

> 
> Jason
> 

Mika