path: root/Documentation
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authorDavid Sterba <>2016-07-08 17:04:25 +0200
committerDavid Sterba <>2016-07-13 18:44:45 +0200
commite67219255cca7b8e09789b6ca725fc4e9780da73 (patch)
tree4e4509b81a9e33af86d8c5a6962a360b1dd327ae /Documentation
parent08c70e18defee0eed543f5a2ee88beed7a710d5f (diff)
btrfs-progs: docs: man5, document control device
Signed-off-by: David Sterba <>
Diffstat (limited to 'Documentation')
1 files changed, 34 insertions, 0 deletions
diff --git a/Documentation/btrfs-man5.asciidoc b/Documentation/btrfs-man5.asciidoc
index 7dd323fa..467f11bf 100644
--- a/Documentation/btrfs-man5.asciidoc
+++ b/Documentation/btrfs-man5.asciidoc
@@ -14,6 +14,8 @@ tools. Currently covers:
2. file attributes
+3. control device
@@ -455,11 +457,43 @@ When set on a directory, all newly created files will inherit this attribute.
No other attributes are supported. For the complete list please refer to the
`chattr`(1) manual page.
+There's a character special device `/dev/btrfs-control` with major and minor
+numbers 10 and 234 (the device can be found under the 'misc' category).
+$ ls -l /dev/btrfs-control
+crw------- 1 root root 10, 234 Jan 1 12:00 /dev/btrfs-control
+The device accepts some ioctl calls that can perform following actions on the
+filesyste module:
+* scan devices for btrfs filesytem (ie. to let multi-device filesystems mount
+ automatically) and register them with the kernel module
+* similar to scan, but also wait until the device scanning process is finished
+ for a given filesystem
+* get the supported features (can be also found under '/sys/fs/btrfs/features')
+The device is usually created by ..., but can be created manually:
+# mknod --mode=600 c 10 234 /dev/btrfs-control
+The device is not strictly required but the device scanning will not work and a
+workaround would need to be used to mount a multi-device filesystem. The mount
+option 'device' can trigger the device scanning during mount.