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

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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






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