[Devel] [PATCH RH9 v3 1/8] block/fops: add llseek_hole to blockdevops

[Andrey Zhadchenko]

Add new function for block_device_operations, which will be used
for SEEK_HOLE and SEEK_DATA llseek calls

Feature: dm: implement SEEK_HOLE for dm-qcow2 and dm-ploop
https://jira.vzint.dev/browse/PSBM-145746
Signed-off-by: Andrey Zhadchenko <andrey.zhadchenko at virtuozzo.com>

---
v2: fix critical bug: do not (SEEK_HOLE | SEEK_DATA) as they are
rather continious enums
v3: add new helper to handle edge cases

 block/fops.c           | 38 ++++++++++++++++++++++++++++++++++++++
 include/linux/blkdev.h |  1 +
 2 files changed, 39 insertions(+)

diff --git a/block/fops.c b/block/fops.c
index 0d07e6f6b284..edd97923a7f1 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -424,6 +424,31 @@ const struct address_space_operations def_blk_aops = {
 	.is_dirty_writeback = buffer_check_dirty_writeback,
 };
 
+static loff_t blkdev_llseek_wrapper(struct block_device *bdev, loff_t offset, int whence)
+{
+	loff_t retval, bd_size;
+
+	bd_size = i_size_read(bdev->bd_inode);
+	if (offset >= bd_size)
+		return -ENXIO;
+
+	retval = bdev->bd_disk->fops->llseek_hole(bdev, offset, whence);
+	if (retval < 0)
+		return retval;
+
+	if (retval < offset)
+		retval = offset;
+
+	if (retval >= bd_size) {
+		if (whence & SEEK_DATA)
+			retval = -ENXIO;
+		if (whence & SEEK_HOLE)
+			retval = bd_size;
+	}
+
+	return retval;
+}
+
 /*
  * for a block special file file_inode(file)->i_size is zero
  * so we compute the size by hand (just as in block_read/write above)
@@ -431,11 +456,24 @@ const struct address_space_operations def_blk_aops = {
 static loff_t blkdev_llseek(struct file *file, loff_t offset, int whence)
 {
 	struct inode *bd_inode = bdev_file_inode(file);
+	struct block_device *bdev = I_BDEV(bd_inode);
+	bool is_llseek_hole;
 	loff_t retval;
 
+	is_llseek_hole = (whence == SEEK_HOLE || whence == SEEK_DATA);
+	if (is_llseek_hole && bdev->bd_disk->fops->llseek_hole) {
+		retval = blkdev_llseek_wrapper(bdev, offset, whence);
+		if (retval < 0)
+			return retval;
+
+		offset = retval;
+		whence = SEEK_SET;
+	}
+
 	inode_lock(bd_inode);
 	retval = fixed_size_llseek(file, offset, whence, i_size_read(bd_inode));
 	inode_unlock(bd_inode);
+
 	return retval;
 }
 
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 8b82a63500fc..5c10935cb38e 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1482,6 +1482,7 @@ struct block_device_operations {
 	int (*getgeo)(struct block_device *, struct hd_geometry *);
 	int (*set_read_only)(struct block_device *bdev, bool ro);
 	void (*free_disk)(struct gendisk *disk);
+	loff_t (*llseek_hole)(struct block_device *bdev, loff_t offset, int whence);
 	/* this callback is with swap_lock and sometimes page table lock held */
 	void (*swap_slot_free_notify) (struct block_device *, unsigned long);
 	int (*report_zones)(struct gendisk *, sector_t sector,
-- 
2.39.3