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Date:   Thu, 10 Mar 2022 22:15:04 -0800
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Subject: Re: [PATCH v2] mm/hmm/test: simplify hmm test code: use miscdevice
 instead of char dev
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To:     mpenttil@redhat.com, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Cc:     apopple@nvidia.com, rcampbell@nvidia.com, jgg@ziepe.ca,
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References: <20220311033050.22724-1-mpenttil@redhat.com>
From:   John Hubbard <jhubbard@nvidia.com>
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On 3/10/22 19:30, mpenttil@redhat.com wrote:
> From: Mika Penttilä <mpenttil@redhat.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.
> 
> This duplicates a fair amount of boilerplate that misc device can do
> instead.
> 
> Change this to use misc device, which makes the device node names appear
> for us. This also enables udev-like processing if desired.
> 
> Delete the /proc/devices parsing from the user-space test script, now
> that it is unnecessary.
> 
> v2:
>          - Cleanups per review comments from John Hubbard
>          - Added Tested-by and Ccs

The three lines above, starting with "v2:", belong after the "---". That
way, they are not included in the commit log. That's the convention.

I think Andrew can fix it up for you, no need to spin a new patch for
that.

Anyway, this looks good now, so please feel free to add:

Reviewed-by: John Hubbard <jhubbard@nvidia.com>


thanks,
-- 
John Hubbard
NVIDIA

> 
> Signed-off-by: Mika Penttilä <mpenttil@redhat.com>
> Tested-by: Alistair Popple <apopple@nvidia.com>
> Cc: John Hubbard <jhubbard@nvidia.com>
> Cc: Ralph Campbell <rcampbell@nvidia.com>
> Cc: Jason Gunthorpe <jgg@ziepe.ca>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> ---
>   lib/test_hmm.c                         | 40 ++++++++++++--------------
>   tools/testing/selftests/vm/test_hmm.sh |  6 ----
>   2 files changed, 19 insertions(+), 27 deletions(-)
> 
> diff --git a/lib/test_hmm.c b/lib/test_hmm.c
> index 767538089a62..0e1488e1bad8 100644
> --- a/lib/test_hmm.c
> +++ b/lib/test_hmm.c
> @@ -10,7 +10,6 @@
>   #include <linux/mm.h>
>   #include <linux/module.h>
>   #include <linux/kernel.h>
> -#include <linux/cdev.h>
>   #include <linux/device.h>
>   #include <linux/mutex.h>
>   #include <linux/rwsem.h>
> @@ -25,18 +24,24 @@
>   #include <linux/swapops.h>
>   #include <linux/sched/mm.h>
>   #include <linux/platform_device.h>
> +#include <linux/miscdevice.h>
>   #include <linux/rmap.h>
>   
>   #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;
>   
>   struct dmirror_device;
>   
> @@ -82,7 +87,7 @@ struct dmirror_chunk {
>    * Per device data.
>    */
>   struct dmirror_device {
> -	struct cdev		cdevice;
> +	struct miscdevice	miscdevice;
>   	struct hmm_devmem	*devmem;
>   
>   	unsigned int		devmem_capacity;
> @@ -118,7 +123,6 @@ static void dmirror_bounce_fini(struct dmirror_bounce *bounce)
>   
>   static int dmirror_fops_open(struct inode *inode, struct file *filp)
>   {
> -	struct cdev *cdev = inode->i_cdev;
>   	struct dmirror *dmirror;
>   	int ret;
>   
> @@ -127,12 +131,13 @@ static int dmirror_fops_open(struct inode *inode, struct file *filp)
>   	if (dmirror == NULL)
>   		return -ENOMEM;
>   
> -	dmirror->mdevice = container_of(cdev, struct dmirror_device, cdevice);
> +	dmirror->mdevice = container_of(filp->private_data,
> +					struct dmirror_device, miscdevice);
>   	mutex_init(&dmirror->mutex);
>   	xa_init(&dmirror->pt);
>   
>   	ret = mmu_interval_notifier_insert(&dmirror->notifier, current->mm,
> -				0, ULONG_MAX & PAGE_MASK, &dmirror_min_ops);
> +					0, ULONG_MAX & PAGE_MASK, &dmirror_min_ops);
>   	if (ret) {
>   		kfree(dmirror);
>   		return ret;
> @@ -1216,16 +1221,16 @@ static const struct dev_pagemap_ops dmirror_devmem_ops = {
>   
>   static int dmirror_device_init(struct dmirror_device *mdevice, int id)
>   {
> -	dev_t dev;
>   	int ret;
>   
> -	dev = MKDEV(MAJOR(dmirror_dev), id);
>   	mutex_init(&mdevice->devmem_lock);
>   	spin_lock_init(&mdevice->lock);
>   
> -	cdev_init(&mdevice->cdevice, &dmirror_fops);
> -	mdevice->cdevice.owner = THIS_MODULE;
> -	ret = cdev_add(&mdevice->cdevice, dev, 1);
> +	mdevice->miscdevice.minor = MISC_DYNAMIC_MINOR;
> +	mdevice->miscdevice.name = dmirror_device_names[id];
> +	mdevice->miscdevice.fops = &dmirror_fops;
> +
> +	ret = misc_register(&mdevice->miscdevice);
>   	if (ret)
>   		return ret;
>   
> @@ -1252,7 +1257,7 @@ static void dmirror_device_remove(struct dmirror_device *mdevice)
>   		kfree(mdevice->devmem_chunks);
>   	}
>   
> -	cdev_del(&mdevice->cdevice);
> +	misc_deregister(&mdevice->miscdevice);
>   }
>   
>   static int __init hmm_dmirror_init(void)
> @@ -1260,11 +1265,6 @@ static int __init hmm_dmirror_init(void)
>   	int ret;
>   	int id;
>   
> -	ret = alloc_chrdev_region(&dmirror_dev, 0, DMIRROR_NDEVICES,
> -				  "HMM_DMIRROR");
> -	if (ret)
> -		goto err_unreg;
> -
>   	for (id = 0; id < DMIRROR_NDEVICES; id++) {
>   		ret = dmirror_device_init(dmirror_devices + id, id);
>   		if (ret)
> @@ -1277,8 +1277,7 @@ static int __init hmm_dmirror_init(void)
>   err_chrdev:
>   	while (--id >= 0)
>   		dmirror_device_remove(dmirror_devices + id);
> -	unregister_chrdev_region(dmirror_dev, DMIRROR_NDEVICES);
> -err_unreg:
> +
>   	return ret;
>   }
>   
> @@ -1288,7 +1287,6 @@ static void __exit hmm_dmirror_exit(void)
>   
>   	for (id = 0; id < DMIRROR_NDEVICES; id++)
>   		dmirror_device_remove(dmirror_devices + id);
> -	unregister_chrdev_region(dmirror_dev, DMIRROR_NDEVICES);
>   }
>   
>   module_init(hmm_dmirror_init);
> diff --git a/tools/testing/selftests/vm/test_hmm.sh b/tools/testing/selftests/vm/test_hmm.sh
> index 0647b525a625..69f5889f8575 100755
> --- a/tools/testing/selftests/vm/test_hmm.sh
> +++ b/tools/testing/selftests/vm/test_hmm.sh
> @@ -41,17 +41,11 @@ check_test_requirements()
>   load_driver()
>   {
>   	modprobe $DRIVER > /dev/null 2>&1
> -	if [ $? == 0 ]; then
> -		major=$(awk "\$2==\"HMM_DMIRROR\" {print \$1}" /proc/devices)
> -		mknod /dev/hmm_dmirror0 c $major 0
> -		mknod /dev/hmm_dmirror1 c $major 1
> -	fi
>   }
>   
>   unload_driver()
>   {
>   	modprobe -r $DRIVER > /dev/null 2>&1
> -	rm -f /dev/hmm_dmirror?
>   }
>   
>   run_smoke()