[PATCH v4 RESEND] mm: cma: add a simple kernel module as the helper to test CMA

On Thursday 05 July 2012, Barry Song wrote:

From: Barry Song <redacted>

Any write request to /dev/cma_test will let the module to allocate memory from
CMA, for example:

1st time
$ echo 1024 > /dev/cma_test
will require cma_test to request 1MB(1024KB)
2nd time
$ echo 2048 > /dev/cma_test
will require cma_test to request 2MB(2048KB)

Any read request to /dev/cma_test will let the module to free the 1st valid
memory from CMA, for example:

1st time
$ cat /dev/cma_test
will require cma_test to free the 1MB allocated in the first write request
2nd time
$ cat /dev/cma_test
will require cma_test to free the 2MB allocated in the second write request

I missed the earlier times this was posted and read up on it now.

Signed-off-by: Barry Song <redacted>
Reviewed-by: Michal Nazarewicz <redacted>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 resend to Greg KH so that he can decide whether it should be placed at tools
 or drivers/misc;
 See the discussion thread:
 [1] https://lkml.org/lkml/2012/7/3/80
 [2] https://lkml.org/lkml/2012/7/3/224
 [3] https://lkml.org/lkml/2012/7/4/87

I think it should be in mm/cma-test.c, along with kmemleak-test.c. It would be nice
if you could add some code that just runs at boot time (or when the module is
loaded) and allocates and frees memory using CMA.

+static struct device *cma_dev;

Do you actually need this device? It's not connected to hardware so
it doesn't actually do DMA and we might as well pass a NULL pointer
into dma_alloc_*().

+static const struct file_operations cma_test_fops = {
+	.owner =    THIS_MODULE,
+	.read  =    cma_test_read,
+	.write =    cma_test_write,
+};
+
+static struct miscdevice cma_test_misc = {
+	.name = "cma_test",
+	.fops = &cma_test_fops,
+};
+
+static int __init cma_test_init(void)
+{
+	int ret = misc_register(&cma_test_misc);

A better place for this is really debugfs. The driver is not meant as a stable
kernel interface that applications can rely on, it's purely a debugging help.

Just make this

	ret = debugfs_create_file("cma-test", 0600, NULL, NULL, &cma_test_fops);



	Arnd