[PATCHv9 3/7] block: allow ability to limit partition write hints

[Keith Busch <kbusch@meta.com>]

From: Keith Busch <kbusch@kernel.org>

When multiple partitions are used, you may want to enforce different
subsets of the available write hints for each partition. Provide a
bitmap attribute of the available write hints, and allow an admin to
write a different mask to set the partition's allowed write hints.

Signed-off-by: Keith Busch <kbusch@kernel.org>
---
 block/bdev.c              | 15 +++++++++++++
 block/partitions/core.c   | 46 +++++++++++++++++++++++++++++++++++++--
 include/linux/blk_types.h |  1 +
 3 files changed, 60 insertions(+), 2 deletions(-)

diff --git a/block/bdev.c b/block/bdev.c
index 738e3c8457e7f..5d23648db457b 100644
--- a/block/bdev.c
+++ b/block/bdev.c
@@ -414,6 +414,7 @@ void __init bdev_cache_init(void)
 
 struct block_device *bdev_alloc(struct gendisk *disk, u8 partno)
 {
+	unsigned short max_write_hints;
 	struct block_device *bdev;
 	struct inode *inode;
 
@@ -440,6 +441,20 @@ struct block_device *bdev_alloc(struct gendisk *disk, u8 partno)
 		return NULL;
 	}
 	bdev->bd_disk = disk;
+
+	max_write_hints = bdev_max_write_hints(bdev);
+	if (max_write_hints) {
+		int size = BITS_TO_LONGS(max_write_hints) * sizeof(long);
+
+		bdev->write_hint_mask = kmalloc(size, GFP_KERNEL);
+		if (!bdev->write_hint_mask) {
+			free_percpu(bdev->bd_stats);
+			iput(inode);
+			return NULL;
+		}
+		memset(bdev->write_hint_mask, 0xff, size);
+	}
+
 	return bdev;
 }
 
diff --git a/block/partitions/core.c b/block/partitions/core.c
index 815ed33caa1b8..c0ea0a7b6fa87 100644
--- a/block/partitions/core.c
+++ b/block/partitions/core.c
@@ -203,6 +203,42 @@ static ssize_t part_discard_alignment_show(struct device *dev,
 	return sprintf(buf, "%u\n", bdev_discard_alignment(dev_to_bdev(dev)));
 }
 
+static ssize_t part_write_hint_mask_show(struct device *dev,
+					 struct device_attribute *attr,
+					 char *buf)
+{
+	struct block_device *bdev = dev_to_bdev(dev);
+	unsigned short max_write_hints = bdev_max_write_hints(bdev);
+
+	if (max_write_hints)
+		return sprintf(buf, "%*pb\n", max_write_hints, bdev->write_hint_mask);
+	else
+		return sprintf(buf, "0");
+}
+
+static ssize_t part_write_hint_mask_store(struct device *dev,
+					  struct device_attribute *attr,
+					  const char *buf, size_t count)
+{
+	struct block_device *bdev = dev_to_bdev(dev);
+	unsigned short max_write_hints = bdev_max_write_hints(bdev);
+	unsigned long *new_mask;
+	int size;
+
+	if (!max_write_hints)
+		return count;
+
+	size = BITS_TO_LONGS(max_write_hints) * sizeof(long);
+	new_mask = kzalloc(size, GFP_KERNEL);
+	if (!new_mask)
+		return -ENOMEM;
+
+	bitmap_parse(buf, count, new_mask, max_write_hints);
+	bitmap_copy(bdev->write_hint_mask, new_mask, max_write_hints);
+
+	return count;
+}
+
 static DEVICE_ATTR(partition, 0444, part_partition_show, NULL);
 static DEVICE_ATTR(start, 0444, part_start_show, NULL);
 static DEVICE_ATTR(size, 0444, part_size_show, NULL);
@@ -211,6 +247,8 @@ static DEVICE_ATTR(alignment_offset, 0444, part_alignment_offset_show, NULL);
 static DEVICE_ATTR(discard_alignment, 0444, part_discard_alignment_show, NULL);
 static DEVICE_ATTR(stat, 0444, part_stat_show, NULL);
 static DEVICE_ATTR(inflight, 0444, part_inflight_show, NULL);
+static DEVICE_ATTR(write_hint_mask, 0644, part_write_hint_mask_show,
+		   part_write_hint_mask_store);
 #ifdef CONFIG_FAIL_MAKE_REQUEST
 static struct device_attribute dev_attr_fail =
 	__ATTR(make-it-fail, 0644, part_fail_show, part_fail_store);
@@ -225,6 +263,7 @@ static struct attribute *part_attrs[] = {
 	&dev_attr_discard_alignment.attr,
 	&dev_attr_stat.attr,
 	&dev_attr_inflight.attr,
+	&dev_attr_write_hint_mask.attr,
 #ifdef CONFIG_FAIL_MAKE_REQUEST
 	&dev_attr_fail.attr,
 #endif
@@ -245,8 +284,11 @@ static const struct attribute_group *part_attr_groups[] = {
 
 static void part_release(struct device *dev)
 {
-	put_disk(dev_to_bdev(dev)->bd_disk);
-	bdev_drop(dev_to_bdev(dev));
+	struct block_device *part = dev_to_bdev(dev);
+
+	kfree(part->write_hint_mask);
+	put_disk(part->bd_disk);
+	bdev_drop(part);
 }
 
 static int part_uevent(const struct device *dev, struct kobj_uevent_env *env)
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index 6737795220e18..af430e543f7f7 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -73,6 +73,7 @@ struct block_device {
 #ifdef CONFIG_SECURITY
 	void			*bd_security;
 #endif
+	unsigned long		*write_hint_mask;
 	/*
 	 * keep this out-of-line as it's both big and not needed in the fast
 	 * path
-- 
2.43.5