Stability	provisional
Portability	non-portable (requires Linux)
Safe Haskell	Safe
Language	Haskell2010

System.Linux.FileExtents

Contents

Extent flags
Extents
Request flags
Getting extent information

Description

This module can be used to retrieve information about how a particular file is stored on disk (i.e. the file fragmentation). It accomplishes that by directly calling the FIEMAP ioctl provided by recent versions of the Linux kernel. This ioctl is specific to Linux and therefore this module is not portable.

For more information about the FIEMAP ioctl see filesystems/fiemap.txt in the kernel documentation.

Synopsis

Extent flags

See filesystems/fiemap.txt in the kernel documentation for a more detailed description of each of these flags.

type ExtentFlags = Word32 #

efLast :: ExtentFlags #

Last extent in file.

efUnknown :: ExtentFlags #

Data location unknown.

efDelalloc :: ExtentFlags #

Location still pending.

efEncoded :: ExtentFlags #

Data cannot be read while fs is unmounted.

efDataEncrypted :: ExtentFlags #

Data is encrypted by fs.

efNotAligned :: ExtentFlags #

Extent offsets may not be block aligned.

efDataInline :: ExtentFlags #

Data mixed with metadata.

efDataTail :: ExtentFlags #

Multiple files in block.

efUnwritten :: ExtentFlags #

Space allocated, but no data (i.e. zero).

efMerged :: ExtentFlags #

File does not natively support extents. Result merged for efficiency.

efShared :: ExtentFlags #

Space shared with other files.

Extents

data Extent #

Description of a single extent. All offsets and lengths are in bytes.

Constructors

Extent
Fields extLogical :: Word64 Offset relative to the beginning of the file. extPhysical :: Word64 Offset relative to the beginning of the underlying block device. extLength :: Word64 The length of the extent. extFlags :: ExtentFlags Flags for this extent.

Instances

Eq Extent #
Methods (==) :: Extent -> Extent -> Bool # (/=) :: Extent -> Extent -> Bool #
Show Extent #
Methods showsPrec :: Int -> Extent -> ShowS # show :: Extent -> String # showList :: [Extent] -> ShowS #
Storable Extent #
Methods sizeOf :: Extent -> Int # alignment :: Extent -> Int # peekElemOff :: Ptr Extent -> Int -> IO Extent # pokeElemOff :: Ptr Extent -> Int -> Extent -> IO () # peekByteOff :: Ptr b -> Int -> IO Extent # pokeByteOff :: Ptr b -> Int -> Extent -> IO () # peek :: Ptr Extent -> IO Extent # poke :: Ptr Extent -> Extent -> IO () #

Request flags

data ReqFlags #

Flags the modify the behavior of extent information requests.

Constructors

ReqFlags
Fields rfSync :: Bool Sync the file before requesting its extents. rfXattr :: Bool Retrieve the extents of the inode's extended attribute lookup tree, instead of its data tree. rfCache :: Bool Request caching of the extents (not supported by older kernels).

Instances

Eq ReqFlags #
Methods (==) :: ReqFlags -> ReqFlags -> Bool # (/=) :: ReqFlags -> ReqFlags -> Bool #
Show ReqFlags #
Methods showsPrec :: Int -> ReqFlags -> ShowS # show :: ReqFlags -> String # showList :: [ReqFlags] -> ShowS #

defReqFlags :: ReqFlags #

Default values for the request flags. All options are disabled.

Getting extent information

getExtentsFd #

Arguments

:: ReqFlags
-> Fd
-> Maybe (Word64, Word64)	The range (offset and length) within the file to look extents for. Use `Nothing` for the entire file.
-> IO [Extent]

Retrieve the list of all extents associated with the file referenced by the file descriptor. Extents returned mirror those on disk - that is, the logical offset of the first returned extent may start before the requested range, and the last returned extent may end after the end of the requested range.

Note: getExtentsFd might call the FIEMAP ioctl multiple times in order to retrieve all the extents of the file. This is necessary when the file has too many fragments. If the file is modified in the meantime, the returned list might be inconsistent.

getExtents :: ReqFlags -> FilePath -> Maybe (Word64, Word64) -> IO [Extent] #

Like getExtentsFd except that it operates on file paths instead of file descriptors.

getExtentCountFd :: ReqFlags -> Fd -> Maybe (Word64, Word64) -> IO Word32 #

Like getExtentsFd except that it returns the number of extents instead of a list.

getExtentCount :: ReqFlags -> FilePath -> Maybe (Word64, Word64) -> IO Word32 #

Like getExtents except that it returns the number of extents instead of a list.