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

[Mika Penttilä]

On 25.3.2022 20.17, Jason Gunthorpe wrote:
> On Tue, Mar 22, 2022 at 06:35:43AM +0200, mpenttil@xxxxxxxxxx wrote:
> > From: Mika Penttilä <mpenttil@xxxxxxxxxx>
> >
> > 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@xxxxxxxxxx>
> > Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx>
> > Cc: Alistair Popple <apopple@xxxxxxxxxx>
> > Cc: Ralph Campbell <rcampbell@xxxxxxxxxx>
> > Cc: Jason Gunthorpe <jgg@xxxxxxxx>
> > Cc: Vlastimil Babka <vbabka@xxxxxxx>
> > 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