linux-kernel - [RFC PATCH 4/7] Increment diskseq when releasing a loop device

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Date:   Wed, 25 Jan 2023 22:33:56 -0500
From:   Demi Marie Obenour <demi@...isiblethingslab.com>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Demi Marie Obenour <demi@...isiblethingslab.com>,
        Marek Marczykowski-Górecki 
        <marmarek@...isiblethingslab.com>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [RFC PATCH 4/7] Increment diskseq when releasing a loop device

This ensures that userspace is aware that the device may now point to
something else.

Signed-off-by: Demi Marie Obenour <demi@...isiblethingslab.com>
---
 block/genhd.c        | 1 +
 drivers/block/loop.c | 6 ++++++
 2 files changed, 7 insertions(+)

diff --git a/block/genhd.c b/block/genhd.c
index 23cf83b3331cdea5c916fbf01cb5b92aeb2f7cf8..5bf7664273c66d04b40730434f17f7b65fbfe101 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -1490,3 +1490,4 @@ void inc_diskseq(struct gendisk *disk)
 {
 	disk->diskseq = atomic64_inc_return(&diskseq);
 }
+EXPORT_SYMBOL(inc_diskseq);
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 1518a6423279bc890221e8184a8f2e420cb16715..f862b0ab1dce43b3617b1381be8e2de3aab828b1 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1205,6 +1205,12 @@ static void __loop_clr_fd(struct loop_device *lo, bool release)
 	if (!part_shift)
 		set_bit(GD_SUPPRESS_PART_SCAN, &lo->lo_disk->state);
 	mutex_lock(&lo->lo_mutex);
+
+	/*
+	 * Increment the disk sequence number, so that userspace knows this
+	 * device now points to something else.
+	 */
+	inc_diskseq(lo->lo_disk);
 	lo->lo_state = Lo_unbound;
 	mutex_unlock(&lo->lo_mutex);
 
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab