System.Linux.Btrfs

Most functions in this module come in two flavors: one that operates on file descriptors and another one that operates on file paths. The former can be distinguished by the Fd suffix in their names.

Basic types

type FileSize = Word64

type ObjectType = Word8

type ObjectId = Word64

type InodeNum = ObjectId

type SubvolId = ObjectId

data CompressionType

Constructors

Zlib

LZO

Instances

Bounded CompressionType

Enum CompressionType

Eq CompressionType

Read CompressionType

Show CompressionType

File cloning

cloneFd :: Fd -> Fd -> IO ()

clone

Arguments

:: FilePath

The source file.

-> FilePath

The destination file.

-> IO ()

Clone an entire file to an existing file.

Note: calls the BTRFS_IOC_CLONE ioctl.

cloneNew :: FilePath -> FilePath -> IO ()

Like clone except that it will create or truncate the destination file if necessary. This is similar to cp --reflink=always.

Note: calls the BTRFS_IOC_CLONE ioctl.

cloneRangeFd :: Fd -> FileSize -> FileSize -> Fd -> FileSize -> IO ()

cloneRange

Arguments

:: FilePath

The source file.

-> FileSize

The offset within the source file.

-> FileSize

The length of the range. A length of 0 selects the range from the source offset to the end.

-> FilePath

The destination file.

-> FileSize

The offset within the destination file.

-> IO ()

Clones a range of bytes from a file to another file. All ranges must be block-aligned.

Note: calls the BTRFS_IOC_CLONE_RANGE ioctl.

data CloneResult

The result of a cloneRangeIfSame operation.

Constructors

CRError IOError

Cloning failed because of an error.

CRDataDiffers

No cloning was performed because the contents of the source and the destination file differ.

CRSuccess FileSize

Cloning succeeded, the returned integer indicates the number of bytes that were deduped.

Instances

Eq CloneResult

Show CloneResult

cloneRangeIfSameFd :: Fd -> FileSize -> FileSize -> [(Fd, FileSize)] -> IO [CloneResult]

cloneRangeIfSame

Arguments

:: FilePath

The source file.

-> FileSize

The offset within the source file.

-> FileSize

The length of the range.

-> [(FilePath, FileSize)]

The destination files and corresponding offsets.

-> IO [CloneResult]

Similar to cloneRange except that it performs the cloning only if the data ranges contain identical data. Additionally, it accepts multiple destination files. The same thing can be accomplished with cloneRange in conjunction with file locking but this function uses in-kernel locking to guarantee that the deduplicated data is identical at the time of the operation. On the other hand, this function will not clone arbitrarily large ranges; the kernel has an upper limit for the length and if cloning bigger ranges is desired then it has to be called multiple times. Note that cloning may succeed for some of the destination files and fail for others. Because of that, this function returns a list of outcomes, one for each destination file, and no exceptions will be raised for the failed files.

Note: calls the BTRFS_IOC_FILE_EXTENT_SAME ioctl.

Requires Linux 3.12 or later.

Subvolumes and snapshots

createSubvol :: FilePath -> IO ()

Create an (initially) empty new subvolume.

Note: calls the BTRFS_IOC_SUBVOL_CREATE ioctl.

destroySubvol :: FilePath -> IO ()

Destroy (delete) a subvolume.

Note: calls the BTRFS_IOC_SNAP_DESTROY ioctl.

snapshotFd :: Fd -> FilePath -> Bool -> IO ()

snapshot

Arguments

:: FilePath

The source subvolume.

-> FilePath

The destination subvolume (must not exist).

-> Bool

Create a read-only snapshot?

-> IO ()

Create a snapshot of an existing subvolume.

Note: calls the BTRFS_IOC_SNAP_CREATE_V2 ioctl.

getSubvolReadOnlyFd :: Fd -> IO Bool

getSubvolReadOnly :: FilePath -> IO Bool

Is the subvolume read-only?

Note: calls the BTRFS_IOC_SUBVOL_GETFLAGS ioctl.

setSubvolReadOnlyFd :: Fd -> Bool -> IO ()

setSubvolReadOnly :: FilePath -> Bool -> IO ()

Make a subvolume read-only (or read-write).

Note: calls the BTRFS_IOC_SUBVOL_GETFLAGS and BTRFS_IOC_SUBVOL_SETFLAGS ioctls.

getSubvolFd :: Fd -> IO SubvolId

getSubvol :: FilePath -> IO SubvolId

Find the id of the subvolume where the given file resides. This is merely a wrapper around lookupInode provided for convenience.

lookupSubvolFd :: Fd -> SubvolId -> IO (SubvolId, InodeNum, FilePath)

lookupSubvol

Arguments

:: FilePath

The mount point of the volume (or any file in that volume).

-> SubvolId

The id of the subvolume.

-> IO (SubvolId, InodeNum, FilePath)

Given the id of a subvolume, find the id of the parent subvolume, the inode number of the directory containing it, and its name. This is a wrapper around treeSearch.

resolveSubvolFd :: Fd -> SubvolId -> IO FilePath

resolveSubvol

Arguments

:: FilePath

The mount point of the volume (or any file in that volume).

-> SubvolId

The id of the subvolume.

-> IO FilePath

Given the id of a subvolume, find its path relative to the root of the volume. This function calls lookupSubvol recursively.

rootSubvol :: SubvolId

The id the root subvolume.

listSubvolsFd :: Fd -> IO [(SubvolId, SubvolId, InodeNum, FilePath)]

listSubvols :: FilePath -> IO [(SubvolId, SubvolId, InodeNum, FilePath)]

Find all subvolumes of the given volume. For each subvolume found, it returns: its id, the id of its parent subvolume, the inode number of the directory containing it, and its name. This is a wrapper around treeSearch.

listSubvolPathsFd :: Fd -> IO [(SubvolId, SubvolId, FilePath)]

listSubvolPaths :: FilePath -> IO [(SubvolId, SubvolId, FilePath)]

Find all subvolumes of the given volume. For each subvolume found, it returns: its id, the id of its parent subvolume, and its path relative to the root of the volume. This is a wrapper around treeSearch and resolveSubvol.

childSubvolsFd :: Fd -> SubvolId -> IO [(SubvolId, InodeNum, FilePath)]

childSubvols

Arguments

:: FilePath

The mount point of the volume (or any file in that volume).

-> SubvolId

The id of the subvolume.

-> IO [(SubvolId, InodeNum, FilePath)]

Find all child subvolumes of the given subvolume. For each child, returns its id, the inode number of the directory containing it, and its name. This is a wrapper around treeSearch.

childSubvolPathsFd :: Fd -> SubvolId -> IO [(SubvolId, FilePath)]

childSubvolPaths

Arguments

:: FilePath

The mount point of the volume (or any file in that volume).

-> SubvolId

The id of the subvolume.

-> IO [(SubvolId, FilePath)]

Find all child subvolumes of the given subvolume. For each child, returns its id and its path relative to the root of the parent. This is a wrapper around treeSearch and lookupInode.

data SubvolInfo

Information about a subvolume.

Constructors

SubvolInfo

Fields

siGeneration :: Word64

The generation when the subvolume was last modified.

siLastSnapshot :: Maybe Word64

The generation when the most recent snapshot of this subvolume was taken.

siParSnapGen :: Maybe Word64

The generation of the snapshot parent at the time when the snapshot was taken. Defined if only if this is a snapshot.

siReadOnly :: Bool

Is this a read-only subvolume?

siUuid :: Maybe UUID

The UUID of the subvolume.

siPUuid :: Maybe UUID

The UUID of the snapshot parent.

siReceivedUuid :: Maybe UUID

The UUID of the source subvolume that this subvolume was received from. This is always defined for received subvolumes.

siCTransId :: Maybe Word64

The generation when an inode was last modified.

siOTransId :: Maybe Word64

The generation when the subvolume was created.

siSTransId :: Maybe Word64

The generation of the source subvolume that this subvolume was received from. This is always defined for received subvolumes.

siRTransId :: Maybe Word64

The generation when the subvolume was received. This is always defined for received subvolumes.

siCTime :: Maybe UTCTime

The time when an inode was last modified.

siOTime :: Maybe UTCTime

The time when the subvolume was created.

siSTime :: Maybe UTCTime

The timestamp that corresponds to siSTransId.

siRTime :: Maybe UTCTime

The time when the subvolume was received. This is always defined for received subvolumes.

Instances

Eq SubvolInfo

Show SubvolInfo

getSubvolInfoFd :: Fd -> SubvolId -> IO SubvolInfo

getSubvolInfo

Arguments

:: FilePath

The mount point of the volume (or any file in that volume).

-> SubvolId

The id of the subvolume.

-> IO SubvolInfo

Retrieve information about a subvolume.

getSubvolByUuidFd :: Fd -> UUID -> IO SubvolId

getSubvolByUuid

Arguments

:: FilePath

The mount point of the volume (or any file in that volume).

-> UUID

The UUID of the subvolume.

-> IO SubvolId

Find the id of a subvolume, given its UUID.

Requires Linux 3.12 or later.

getSubvolByReceivedUuidFd :: Fd -> UUID -> IO SubvolId

getSubvolByReceivedUuid

Arguments

:: FilePath

The mount point of the volume (or any file in that volume).

-> UUID

The siReceivedUuid of the subvolume.

-> IO SubvolId

Find the id of a subvolume, given its siReceivedUuid.

Requires Linux 3.12 or later.

Defragging

defragFd :: Fd -> IO ()

defrag :: FilePath -> IO ()

Defrag a single file.

Note: calls the BTRFS_IOC_DEFRAG ioctl.

data DefragRangeArgs

Argument to the defragRange operation.

Constructors

DefragRangeArgs

Fields

draStart :: FileSize

Beginning of the defrag range.

draLength :: FileSize

Number of bytes to defrag, use maxBound to say all.

draExtentThreshold :: Word32

Any extent bigger than this size will be considered already defragged. Use 0 to take the kernel default, use 1 to say every single extent must be rewritten.

draCompress :: Maybe CompressionType

Compress the file while defragmenting.

draFlush :: Bool

Flush data to disk immediately after defragmenting.

defaultDefragRangeArgs :: DefragRangeArgs

Defaults for defragRange. Selects the entire file, no compression, and no flushing.

defragRangeFd :: Fd -> DefragRangeArgs -> IO ()

defragRange :: FilePath -> DefragRangeArgs -> IO ()

Defrag a range within a single file.

Note: calls the BTRFS_IOC_DEFRAG_RANGE ioctl.

Sync

syncFd :: Fd -> IO ()

sync :: FilePath -> IO ()

Sync the file system identified by the supplied path. The FilePath can refer to any file in the file system.

Note: calls the BTRFS_IOC_SYNC ioctl.

startSyncFd :: Fd -> IO ()

startSync :: FilePath -> IO ()

Initiate a sync for the file system identified by the supplied path.

Note: calls the BTRFS_IOC_START_SYNC ioctl.

waitSyncFd :: Fd -> IO ()

waitSync :: FilePath -> IO ()

Wait until the sync operation completes.

Note: calls the BTRFS_IOC_WAIT_SYNC ioctl.

Inspect internal

resolveLogicalFd :: Fd -> FileSize -> IO ([(InodeNum, FileSize, SubvolId)], Int)

resolveLogical

Arguments

:: FilePath

The mount point of the volume (or any file in that volume).

-> FileSize

The physical byte offset in the underlying block device.

-> IO ([(InodeNum, FileSize, SubvolId)], Int)

Given a physical offset, look for any inodes that this byte belongs to. For each inode, it returns the inode number, the logical offset (i.e. the offset within the inode), and the subvolume id. If a large number of inodes is found, then not all of them will be returned by this function. This is due to a current limitation in the kernel. The integer returned along with list of inodes indicates the number of inodes found but not included in the list.

Note: calls the BTRFS_IOC_LOGICAL_INO ioctl.

resolveInodeFd :: Fd -> InodeNum -> IO ([FilePath], Int)

resolveInode

Arguments

:: FilePath

The path to the subvolume (or any file in that subvolume).

-> InodeNum

The inode number.

-> IO ([FilePath], Int)

Find the file path(s) given an inode number. Returns a list of file paths and an integer indicating the number of paths found but not included in the resulting list. This is because of a limitation in the kernel (it will not return an arbitrarily large list). The paths returned are relative to the root of the subvolume.

Note: calls the BTRFS_IOC_INO_PATHS ioctl.

lookupInodeFd :: Fd -> SubvolId -> InodeNum -> IO (SubvolId, FilePath)

lookupInode

Arguments

:: FilePath

The path to any file in the volume. The subvolume where this file resides is ignored unless no SubvolId is provided (see below).

-> SubvolId

The id of the subvolume. Can be 0. In that case, the subvolume of the FilePath is used (see above).

-> InodeNum

The inode number.

-> IO (SubvolId, FilePath)

Find the path of a file given its inode number and the id of the subvolume. If multiple files share the same inode number, only one of them is returned. The id of the subvolume is also returned. This is useful when 0 is given for the SubvolId argument (also see getSubvol for this case).

Note: calls the BTRFS_IOC_INO_LOOKUP ioctl.

Miscellaneous

getFileNoCOWFd :: Fd -> IO Bool

getFileNoCOW :: FilePath -> IO Bool

Determine whether the NOCOW flag is enabled for the specified file.

Note: calls the FS_IOC_GETFLAGS ioctl.

setFileNoCOWFd :: Fd -> Bool -> IO ()

setFileNoCOW :: FilePath -> Bool -> IO ()

Set or clear the NOCOW flag for the specified file. If the file is not empty, this has no effect and no error will be reported.

Note: calls the FS_IOC_GETFLAGS and FS_IOC_GETFLAGS ioctls.

Tree search

Low-level API for tree search using the BTRFS_IOC_TREE_SEARCH ioctl.

data SearchKey

Constructors

SearchKey

Fields

skTreeId :: ObjectId

skMinObjectId :: ObjectId

skMinType :: ObjectType

skMinOffset :: Word64

skMaxObjectId :: ObjectId

skMaxType :: ObjectType

skMaxOffset :: Word64

skMinTransId :: Word64

skMaxTransId :: Word64

Instances

Eq SearchKey

Show SearchKey

defaultSearchKey :: SearchKey

data SearchHeader

Constructors

SearchHeader

Fields

shTransId :: Word64

shObjectId :: ObjectId

shOffset :: Word64

shType :: ObjectType

shLen :: Word32

Instances

Eq SearchHeader

Show SearchHeader

treeSearchFd :: Fd -> SearchKey -> Int -> (SearchHeader -> Ptr i -> IO ()) -> IO ()

treeSearch :: FilePath -> SearchKey -> Int -> (SearchHeader -> Ptr i -> IO ()) -> IO ()

treeSearchListFd :: Fd -> SearchKey -> (SearchHeader -> Ptr i -> IO (Maybe a)) -> IO [a]

treeSearchList :: FilePath -> SearchKey -> (SearchHeader -> Ptr i -> IO (Maybe a)) -> IO [a]

findFirstItemFd :: Fd -> SearchKey -> (SearchHeader -> Ptr i -> IO a) -> IO a

findFirstItem :: FilePath -> SearchKey -> (SearchHeader -> Ptr i -> IO a) -> IO a