[PATCHv11 4/9] 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>
---
 Documentation/ABI/stable/sysfs-block |  7 +++++
 block/bdev.c                         | 17 +++++++++++
 block/partitions/core.c              | 45 ++++++++++++++++++++++++++--
 include/linux/blk_types.h            |  1 +
 4 files changed, 68 insertions(+), 2 deletions(-)

diff --git a/Documentation/ABI/stable/sysfs-block b/Documentation/ABI/stable/sysfs-block
index f2db2cabb8e75..fa2db6b638d63 100644
--- a/Documentation/ABI/stable/sysfs-block
+++ b/Documentation/ABI/stable/sysfs-block
@@ -187,6 +187,13 @@ Description:
 		partition is offset from the internal allocation unit's
 		natural alignment.
 
+What:		/sys/block/<disk>/<partition>/write_hint_mask
+Date:		October 2024
+Contact:	linux-block@vger.kernel.org
+Description:
+		The mask of allowed write hints. You can limit which hints the
+		block layer will use by writing a new mask.  Only the first
+		partition can access all the write hints by default.
 
 What:		/sys/block/<disk>/<partition>/stat
 Date:		February 2008
diff --git a/block/bdev.c b/block/bdev.c
index 9a59f0c882170..e6f9d19db599b 100644
--- a/block/bdev.c
+++ b/block/bdev.c
@@ -415,6 +415,7 @@ void __init bdev_cache_init(void)
 struct block_device *bdev_alloc(struct gendisk *disk, u8 partno)
 {
 	struct block_device *bdev;
+	unsigned short write_hint;
 	struct inode *inode;
 
 	inode = new_inode(blockdev_superblock);
@@ -440,6 +441,22 @@ struct block_device *bdev_alloc(struct gendisk *disk, u8 partno)
 		return NULL;
 	}
 	bdev->bd_disk = disk;
+
+	write_hint = bdev_max_write_hints(bdev);
+	if (write_hint) {
+		bdev->write_hint_mask = bitmap_alloc(write_hint, GFP_KERNEL);
+		if (!bdev->write_hint_mask) {
+			free_percpu(bdev->bd_stats);
+			iput(inode);
+			return NULL;
+		}
+
+		if (partno == 1)
+			bitmap_set(bdev->write_hint_mask, 0, write_hint);
+		else
+			bitmap_clear(bdev->write_hint_mask, 0, write_hint);
+	}
+
 	return bdev;
 }
 
diff --git a/block/partitions/core.c b/block/partitions/core.c
index 815ed33caa1b8..c71a5d34339d7 100644
--- a/block/partitions/core.c
+++ b/block/partitions/core.c
@@ -203,6 +203,41 @@ 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, "0");
+	return sprintf(buf, "%*pb\n", max_write_hints, bdev->write_hint_mask);
+}
+
+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;
+
+	if (!max_write_hints)
+		return count;
+
+	new_mask = bitmap_alloc(max_write_hints, 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);
+	smp_wmb();
+	bitmap_free(new_mask);
+
+	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 +246,8 @@ 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 +262,7 @@ 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 +283,11 @@ 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);
+
+	bitmap_free(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