block: restore the write_same_max sysfs attribute

[Christoph Hellwig]

Some userspace breaks if this attribute is gone.  Restore it and always
return 0.

Signed-off-by: Christoph Hellwig <hch at lst.de>
---
 block/blk-sysfs.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 4a5bb47bee3ce..431fdd036f65a 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -212,6 +212,11 @@ static ssize_t queue_discard_zeroes_data_show(struct request_queue *q, char *pag
 	return queue_var_show(0, page);
 }
 
+static ssize_t queue_write_same_max_show(struct request_queue *q, char *page)
+{
+	return sprintf(page, "%llu\n", 0ULL);
+}
+
 static ssize_t queue_write_zeroes_max_show(struct request_queue *q, char *page)
 {
 	return sprintf(page, "%llu\n",
@@ -581,6 +586,7 @@ QUEUE_RO_ENTRY(queue_discard_max_hw, "discard_max_hw_bytes");
 QUEUE_RW_ENTRY(queue_discard_max, "discard_max_bytes");
 QUEUE_RO_ENTRY(queue_discard_zeroes_data, "discard_zeroes_data");
 
+QUEUE_RO_ENTRY(queue_write_same_max, "write_same_max_bytes");
 QUEUE_RO_ENTRY(queue_write_zeroes_max, "write_zeroes_max_bytes");
 QUEUE_RO_ENTRY(queue_zone_append_max, "zone_append_max_bytes");
 QUEUE_RO_ENTRY(queue_zone_write_granularity, "zone_write_granularity");
@@ -636,6 +642,7 @@ static struct attribute *queue_attrs[] = {
 	&queue_discard_max_entry.attr,
 	&queue_discard_max_hw_entry.attr,
 	&queue_discard_zeroes_data_entry.attr,
+	&queue_write_same_max_entry.attr,
 	&queue_write_zeroes_max_entry.attr,
 	&queue_zone_append_max_entry.attr,
 	&queue_zone_write_granularity_entry.attr,
-- 
2.30.2