Stability	provisional
Portability	non-portable (requires Linux)
Safe Haskell	None
Language	Haskell2010

System.Linux.Btrfs

Contents

Basic types
File cloning
Subvolumes and snapshots
Defragging
Sync
Inspect internal
Miscellaneous
Tree search

Description

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.

Synopsis

Basic types

type FileSize = Word64 Source

type ObjectType = Word8 Source

type ObjectId = Word64 Source

type InodeNum = ObjectId Source

type SubvolId = ObjectId Source

File cloning

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

clone Source

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 () Source

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 () Source

cloneRange Source

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 Source

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] Source

cloneRangeIfSame Source

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 () Source

Create an (initially) empty new subvolume.

Note: calls the BTRFS_IOC_SUBVOL_CREATE ioctl.

destroySubvol :: FilePath -> IO () Source

Destroy (delete) a subvolume.

Note: calls the BTRFS_IOC_SNAP_DESTROY ioctl.

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

snapshot Source

Arguments

:: FilePath	The source subvolume.
-> FilePath	The destination subvolume (must not exist).
-> Bool	Make the subvolume read-only?
-> IO ()

Create a snapshot of an existing subvolume.

Note: calls the BTRFS_IOC_SNAP_CREATE_V2 ioctl.

getSubvolReadOnlyFd :: Fd -> IO Bool Source

getSubvolReadOnly :: FilePath -> IO Bool Source

Is the subvolume read-only?

Note: calls the BTRFS_IOC_SUBVOL_GETFLAGS ioctl.

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

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

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 Source

getSubvol :: FilePath -> IO SubvolId Source

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) Source

lookupSubvol Source

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 Source

resolveSubvol Source

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 Source

The id the root subvolume.

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

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

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)] Source

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

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)] Source

childSubvols Source

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)] Source

childSubvolPaths Source

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 Source

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 Source

getSubvolInfo Source

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 Source

getSubvolByUuid Source

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 Source

getSubvolByReceivedUuid Source

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 () Source

defrag :: FilePath -> IO () Source

Defrag a single file.

Note: calls the BTRFS_IOC_DEFRAG ioctl.

Sync

syncFd :: Fd -> IO () Source

sync :: FilePath -> IO () Source

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 () Source

startSync :: FilePath -> IO () Source

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

Note: calls the BTRFS_IOC_START_SYNC ioctl.

waitSyncFd :: Fd -> IO () Source

waitSync :: FilePath -> IO () Source

Wait until the sync operation completes.

Note: calls the BTRFS_IOC_WAIT_SYNC ioctl.

Inspect internal

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

resolveLogical Source

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) Source

resolveInode Source

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 path 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) Source

lookupInode Source

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 Source

getFileNoCOW :: FilePath -> IO Bool Source

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

Note: calls the FS_IOC_GETFLAGS ioctl.

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

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

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 Source

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 Source

data SearchHeader Source

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 () Source

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

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

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

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

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