linux-kernel - [PATCH v4 6/6] docs: device-mapper: 'noexcl' option for dm-linear

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Date:   Wed, 3 Feb 2021 18:53:58 +0300
From:   Sergei Shtepa <sergei.shtepa@...am.com>
To:     <Damien.LeMoal@....com>, <snitzer@...hat.com>, <hare@...e.de>,
        <ming.lei@...hat.com>, <agk@...hat.com>, <corbet@....net>,
        <axboe@...nel.dk>, <jack@...e.cz>, <johannes.thumshirn@....com>,
        <gregkh@...uxfoundation.org>, <koct9i@...il.com>, <steve@....org>,
        <dm-devel@...hat.com>, <linux-block@...r.kernel.org>,
        <linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:     <sergei.shtepa@...am.com>, <pavgel.tide@...am.com>
Subject: [PATCH v4 6/6] docs: device-mapper: 'noexcl' option for dm-linear

New 'noexcl' option allow to open underlying block-device
without FMODE_EXCL flag.

Signed-off-by: Sergei Shtepa <sergei.shtepa@...am.com>
---
 .../admin-guide/device-mapper/linear.rst      | 26 ++++++++++++++++---
 1 file changed, 23 insertions(+), 3 deletions(-)

diff --git a/Documentation/admin-guide/device-mapper/linear.rst b/Documentation/admin-guide/device-mapper/linear.rst
index 9d17fc6e64a9..f035cd7ad78c 100644
--- a/Documentation/admin-guide/device-mapper/linear.rst
+++ b/Documentation/admin-guide/device-mapper/linear.rst
@@ -6,12 +6,22 @@ Device-Mapper's "linear" target maps a linear range of the Device-Mapper
 device onto a linear range of another device.  This is the basic building
 block of logical volume managers.
 
-Parameters: <dev path> <offset>
+Parameters: <dev path> <offset> [<options>]
     <dev path>:
-	Full pathname to the underlying block-device, or a
+        Full pathname to the underlying block-device, or a
         "major:minor" device-number.
     <offset>:
-	Starting sector within the device.
+        Starting sector within the device.
+    <options>:
+        Options allow to set the exclusivity mode. The exclusivity mode
+        can be 'excl' and 'noexcl'. By default, then options is not set,
+        the 'excl' mode is used. 'noexcl' mode allow to open device
+        without FMODE_EXCL flag. This allow to create liner device with
+        underlying block-device that are already used by the system. For
+        example, the file system on this device is already mounted.
+        The 'noexcl' option should be used when creating dm devices that
+        will be used as acceptor when connecting the device mapper to an
+        existing block device with the 'dmsetup remap' command.
 
 
 Example scripts
@@ -61,3 +71,13 @@ Example scripts
   }
 
   `echo \"$table\" | dmsetup create $name`;
+
+::
+
+  #!/bin/sh
+  # Create linear device and remap all requests from the original device
+  # to new linear.
+  DEV=$1
+
+  echo "0 `blockdev --getsz $DEV` linear $DEV 0 noexcl" | dmsetup create dm-noexcl
+  dmsetup remap start dm-noexcl $DEV
-- 
2.20.1