linux-kernel - [PATCH AUTOSEL for 4.15 036/189] dm thin: fix documentation relative to low water mark threshold

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Date:   Mon, 9 Apr 2018 00:17:14 +0000
From:   Sasha Levin <Alexander.Levin@...rosoft.com>
To:     "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     mulhern <amulhern@...hat.com>, Mike Snitzer <snitzer@...hat.com>,
        Sasha Levin <Alexander.Levin@...rosoft.com>
Subject: [PATCH AUTOSEL for 4.15 036/189] dm thin: fix documentation relative
 to low water mark threshold

From: mulhern <amulhern@...hat.com>

[ Upstream commit 9b28a1102efc75d81298198166ead87d643a29ce ]

Fixes:
1. The use of "exceeds" when the opposite of exceeds, falls below,
was meant.
2. Properly speaking, a table can not exceed a threshold.

It emphasizes the important point, which is that it is the userspace
daemon's responsibility to check for low free space when a device
is resumed, since it won't get a special event indicating low free
space in that situation.

Signed-off-by: mulhern <amulhern@...hat.com>
Signed-off-by: Mike Snitzer <snitzer@...hat.com>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
---
 Documentation/device-mapper/thin-provisioning.txt | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/Documentation/device-mapper/thin-provisioning.txt b/Documentation/device-mapper/thin-provisioning.txt
index 1699a55b7b70..ef639960b272 100644
--- a/Documentation/device-mapper/thin-provisioning.txt
+++ b/Documentation/device-mapper/thin-provisioning.txt
@@ -112,9 +112,11 @@ $low_water_mark is expressed in blocks of size $data_block_size.  If
 free space on the data device drops below this level then a dm event
 will be triggered which a userspace daemon should catch allowing it to
 extend the pool device.  Only one such event will be sent.
-Resuming a device with a new table itself triggers an event so the
-userspace daemon can use this to detect a situation where a new table
-already exceeds the threshold.
+
+No special event is triggered if a just resumed device's free space is below
+the low water mark. However, resuming a device always triggers an
+event; a userspace daemon should verify that free space exceeds the low
+water mark when handling this event.
 
 A low water mark for the metadata device is maintained in the kernel and
 will trigger a dm event if free space on the metadata device drops below
-- 
2.15.1