[PATCH v3 4/9] loop: Refactor loop_set_status() size calculation

[Martijn Coenen <maco@android.com>]

figure_loop_size() calculates the loop size based on the passed in
parameters, but at the same time it updates the offset and sizelimit
parameters in the loop device configuration. That is a somewhat
unexpected side effect of a function with this name, and it is only only
needed by one of the two callers of this function - loop_set_status().

Move the lo_offset and lo_sizelimit assignment back into loop_set_status(),
and use the newly factored out functions to validate and apply the newly
calculated size. This allows us to get rid of figure_loop_size in a
follow-up commit.

Signed-off-by: Martijn Coenen <maco@android.com>
---
 drivers/block/loop.c | 39 +++++++++++++++++++++++----------------
 1 file changed, 23 insertions(+), 16 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 2e2874318393..d0f17ee1e29b 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1295,6 +1295,8 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
 	kuid_t uid = current_uid();
 	struct block_device *bdev;
 	bool partscan = false;
+	bool size_changed = false;
+	loff_t validated_size;
 
 	err = mutex_lock_killable(&loop_ctl_mutex);
 	if (err)
@@ -1316,6 +1318,13 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
 
 	if (lo->lo_offset != info->lo_offset ||
 	    lo->lo_sizelimit != info->lo_sizelimit) {
+		loff_t size = get_size(info->lo_offset, info->lo_sizelimit,
+				       lo->lo_backing_file);
+		err = loop_validate_size(size);
+		if (err)
+			goto out_unlock;
+		size_changed = true;
+		validated_size = size;
 		sync_blockdev(lo->lo_device);
 		kill_bdev(lo->lo_device);
 	}
@@ -1323,6 +1332,15 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
 	/* I/O need to be drained during transfer transition */
 	blk_mq_freeze_queue(lo->lo_queue);
 
+	if (size_changed && lo->lo_device->bd_inode->i_mapping->nrpages) {
+		/* If any pages were dirtied after kill_bdev(), try again */
+		err = -EAGAIN;
+		pr_warn("%s: loop%d (%s) has still dirty pages (nrpages=%lu)\n",
+			__func__, lo->lo_number, lo->lo_file_name,
+			lo->lo_device->bd_inode->i_mapping->nrpages);
+		goto out_unfreeze;
+	}
+
 	err = loop_release_xfer(lo);
 	if (err)
 		goto out_unfreeze;
@@ -1346,22 +1364,8 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
 	if (err)
 		goto out_unfreeze;
 
-	if (lo->lo_offset != info->lo_offset ||
-	    lo->lo_sizelimit != info->lo_sizelimit) {
-		/* kill_bdev should have truncated all the pages */
-		if (lo->lo_device->bd_inode->i_mapping->nrpages) {
-			err = -EAGAIN;
-			pr_warn("%s: loop%d (%s) has still dirty pages (nrpages=%lu)\n",
-				__func__, lo->lo_number, lo->lo_file_name,
-				lo->lo_device->bd_inode->i_mapping->nrpages);
-			goto out_unfreeze;
-		}
-		if (figure_loop_size(lo, info->lo_offset, info->lo_sizelimit)) {
-			err = -EFBIG;
-			goto out_unfreeze;
-		}
-	}
-
+	lo->lo_offset = info->lo_offset;
+	lo->lo_sizelimit = info->lo_sizelimit;
 	memcpy(lo->lo_file_name, info->lo_file_name, LO_NAME_SIZE);
 	memcpy(lo->lo_crypt_name, info->lo_crypt_name, LO_NAME_SIZE);
 	lo->lo_file_name[LO_NAME_SIZE-1] = 0;
@@ -1385,6 +1389,9 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
 		lo->lo_key_owner = uid;
 	}
 
+	if (size_changed)
+		loop_set_size(lo, validated_size);
+
 	loop_config_discard(lo);
 
 	/* update dio if lo_offset or transfer is changed */
-- 
2.26.2.303.gf8c07b1a785-goog