btrfs-progs: update manpage with new option -f for btrfstune

The new option -f will force to do dangerous changes.
e.g. clear the seeding flag.

Signed-off-by: Gui Hecheng <guihc.fnst@cn.fujitsu.com>
[more text from 3db4c0a3d35dd5f8 changelog]
Signed-off-by: David Sterba <dsterba@suse.cz>

diff --git a/Documentation/btrfstune.txt b/Documentation/btrfstune.txt
index 56cf66b..d49a974 100644 (file)
--- a/Documentation/btrfstune.txt
+++ b/Documentation/btrfstune.txt
@@ -24,7 +24,14 @@ Enable seeding forces a fs readonly so that you can use it to build other filesy
 Enable extended inode refs.
 -x::
 Enable skinny metadata extent refs.
+-f::
+Allow dangerous changes, e.g. clear the seeding flag
 
+When mounting the new device, btrfs will check whether the seeding flag is set
+when try to open seeding device.  If the user clears the seeding flag of the
+seeding device, the new device will not be mountable. Even setting the seeding
+flag back will not fix this problem, because the generation will be changed at
+that time. Clear the seeding flag may damage the new filesystem.
 
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