linux-kernel - [RFC 6/9] dm-linear: add llseek(SEEK_HOLE/SEEK

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Date: Thu, 28 Mar 2024 16:39:07 -0400
From: Stefan Hajnoczi <stefanha@...hat.com>
To: linux-block@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	eblake@...hat.com,
	Alasdair Kergon <agk@...hat.com>,
	Mikulas Patocka <mpatocka@...hat.com>,
	dm-devel@...ts.linux.dev,
	David Teigland <teigland@...hat.com>,
	Mike Snitzer <snitzer@...nel.org>,
	Jens Axboe <axboe@...nel.dk>,
	Christoph Hellwig <hch@....de>,
	Joe Thornber <ejt@...hat.com>,
	Stefan Hajnoczi <stefanha@...hat.com>
Subject: [RFC 6/9] dm-linear: add llseek(SEEK_HOLE/SEEK_DATA) support

Signed-off-by: Stefan Hajnoczi <stefanha@...hat.com>
---
 drivers/md/dm-linear.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/drivers/md/dm-linear.c b/drivers/md/dm-linear.c
index 2d3e186ca87e3..9b6cdfa4f951d 100644
--- a/drivers/md/dm-linear.c
+++ b/drivers/md/dm-linear.c
@@ -147,6 +147,30 @@ static int linear_report_zones(struct dm_target *ti,
 #define linear_report_zones NULL
 #endif
 
+static loff_t linear_seek_hole_data(struct dm_target *ti, loff_t offset,
+		int whence)
+{
+	struct linear_c *lc = ti->private;
+	loff_t ti_begin = ti->begin << SECTOR_SHIFT;
+	loff_t ti_len = ti->len << SECTOR_SHIFT;
+	loff_t bdev_start = lc->start << SECTOR_SHIFT;
+	loff_t bdev_offset;
+
+	/* TODO underflow/overflow? */
+	bdev_offset = offset - ti_begin + bdev_start;
+
+	bdev_offset = blkdev_seek_hole_data(lc->dev->bdev, bdev_offset,
+					    whence);
+	if (bdev_offset < 0)
+		return bdev_offset;
+
+	offset = bdev_offset - bdev_start;
+	if (offset >= ti_len)
+		return whence == SEEK_DATA ? -ENXIO : ti_begin + ti_len;
+
+	return offset + ti_begin;
+}
+
 static int linear_iterate_devices(struct dm_target *ti,
 				  iterate_devices_callout_fn fn, void *data)
 {
@@ -212,6 +236,7 @@ static struct target_type linear_target = {
 	.direct_access = linear_dax_direct_access,
 	.dax_zero_page_range = linear_dax_zero_page_range,
 	.dax_recovery_write = linear_dax_recovery_write,
+	.seek_hole_data = linear_seek_hole_data,
 };
 
 int __init dm_linear_init(void)
-- 
2.44.0