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libnvdimm, pmem, dax: export a cache control attribute

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The dax_flush() operation can be turned into a nop on platforms where
firmware arranges for cpu caches to be flushed on a power-fail event.
The ACPI 6.2 specification defines a mechanism for the platform to
indicate this capability so the kernel can select the proper default.
However, for other platforms, the administrator must toggle this setting
manually.

Given this flush setting is a dax-specific mechanism we advertise it
through a 'dax' attribute group hanging off a host device. For example,
a 'pmem0' block-device gets a 'dax' sysfs-subdirectory with a
'write_cache' attribute to control response to dax cache flush requests.
This is similar to the 'queue/write_cache' attribute that appears under
block devices.

Cc: Jan Kara <[email protected]>
Cc: Jeff Moyer <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Ross Zwisler <[email protected]>
Suggested-by: Christoph Hellwig <[email protected]>
Signed-off-by: Dan Williams <[email protected]>
This commit is contained in:
Dan Williams 2017-06-26 21:28:41 -07:00
commit 6e0c90d691
3 changed files with 92 additions and 0 deletions
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10
drivers/nvdimm/pmem.c
View file

@ -253,6 +253,11 @@ static const struct dax_operations pmem_dax_ops = {
.flush = pmem_dax_flush,
};
static const struct attribute_group *pmem_attribute_groups[] = {
&dax_attribute_group,
NULL,
};
static void pmem_release_queue(void *q)
{
blk_cleanup_queue(q);
@ -287,6 +292,7 @@ static int pmem_attach_disk(struct device *dev,
struct pmem_device *pmem;
struct resource pfn_res;
struct request_queue *q;
struct device *gendev;
struct gendisk *disk;
void *addr;
@ -384,8 +390,12 @@ static int pmem_attach_disk(struct device *dev,
put_disk(disk);
return -ENOMEM;
}
dax_write_cache(dax_dev, true);
pmem->dax_dev = dax_dev;
gendev = disk_to_dev(disk);
gendev->groups = pmem_attribute_groups;
device_add_disk(dev, disk);
if (devm_add_action_or_reset(dev, pmem_release_disk, pmem))
return -ENOMEM;