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-rw-r--r--Documentation/btrfstune.asciidoc81
1 files changed, 52 insertions, 29 deletions
diff --git a/Documentation/btrfstune.asciidoc b/Documentation/btrfstune.asciidoc
index 2710096..1d6bc98 100644
--- a/Documentation/btrfstune.asciidoc
+++ b/Documentation/btrfstune.asciidoc
@@ -25,26 +25,29 @@ means. Please refer to the 'FILESYSTEM FEATURES' in `btrfs`(5).
OPTIONS
-------
--S <0|1>::
-Enable seeding on a given device. Value 1 will enable seeding, 0 will disable it. +
-A seeding filesystem is forced to be mounted read-only. A new device can be added
-to the filesystem and will capture all writes keeping the seeding device intact.
--r::
-(since kernel: 3.7)
+-f::
+Allow dangerous changes, e.g. clear the seeding flag or change fsid. Make sure
+that you are aware of the dangers.
+
+-m::
+(since kernel: 5.0)
+
-Enable extended inode refs (hardlink limit per file in a directory is 65536),
-enabled by mkfs feature 'extref'.
+change fsid stored as 'metadata_uuid' to a randomly generated UUID,
+see also '-U'
--x::
-(since kernel: 3.10)
+-M <UUID>::
+(since kernel: 5.0)
+
-Enable skinny metadata extent refs (more efficient representation of extents),
-enabled by mkfs feature 'skinny-metadata'.
+change fsid stored as 'metadata_uuid' to a given UUID, see also '-U'
+
-All newly created extents will use the new representation. To completely switch
-the entire filesystem, run a full balance of the metadata. Please refer to
-`btrfs-balance`(8).
+The metadata_uuid is stored only in the superblock and is a backward
+incompatible change. The fsid in metadata blocks remains unchanged and
+is not overwritten, thus the whole operation is significantly faster than
+'-U'.
++
+The new metadata_uuid can be used for mount by UUID and is also used to
+identify devices of a multi-device filesystem.
-n::
(since kernel: 3.14)
@@ -52,33 +55,53 @@ the entire filesystem, run a full balance of the metadata. Please refer to
Enable no-holes feature (more efficient representation of file holes), enabled
by mkfs feature 'no-holes'.
--f::
-Allow dangerous changes, e.g. clear the seeding flag or change fsid. Make sure
-that you are aware of the dangers.
+-r::
+(since kernel: 3.7)
++
+Enable extended inode refs (hardlink limit per file in a directory is 65536),
+enabled by mkfs feature 'extref'.
+
+-S <0|1>::
+Enable seeding on a given device. Value 1 will enable seeding, 0 will disable it. +
+A seeding filesystem is forced to be mounted read-only. A new device can be added
+to the filesystem and will capture all writes keeping the seeding device intact.
++
+WARNING: Clearing the seeding flag on a device may be dangerous.
+If a previously-seeding device is changed, all filesystems that used that
+device will become unmountable. Setting the seeding flag back will not fix
+that. +
+A valid usecase is 'seeding device as a base image'. Clear the seeding
+flag, update the filesystem and make it seeding again, provided that it's OK
+to throw away all filesystems built on top of the previous base.
-u::
Change fsid to a randomly generated UUID or continue previous fsid change
operation in case it was interrupted.
-U <UUID>::
-Change fsid to 'UUID'.
+Change fsid to 'UUID' in all metadata blocks.
+
The 'UUID' should be a 36 bytes string in `printf`(3) format
'"%08x-%04x-%04x-%04x-%012x"'.
If there is a previous unfinished fsid change, it will continue only if the
'UUID' matches the unfinished one or if you use the option '-u'.
-
++
+All metadata blocks are rewritten, this may take some time, but the final
+filesystem compatibility is unaffected, unlike '-M'.
++
WARNING: Cancelling or interrupting a UUID change operation will make the
-filesystem temporarily unmountable. To fix it, rerun 'btrfstune -u' to restore
-the UUID and let it complete.
+filesystem temporarily unmountable. To fix it, rerun 'btrfstune -u' and let
+it complete.
-WARNING: Clearing the seeding flag on a device may be dangerous.
-If a previously-seeding device is changed, all filesystems that used that
-device will become unmountable. Setting the seeding flag back will not fix
-that. +
-A valid usecase is 'seeding device as a base image'. Clear the seeding
-flag, update the filesystem and make it seeding again, provided that it's OK
-to throw away all filesystems built on top of the previous base.
+-x::
+(since kernel: 3.10)
++
+Enable skinny metadata extent refs (more efficient representation of extents),
+enabled by mkfs feature 'skinny-metadata'.
++
+All newly created extents will use the new representation. To completely switch
+the entire filesystem, run a full balance of the metadata. Please refer to
+`btrfs-balance`(8).
EXIT STATUS
-----------