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

efLast :: ExtentFlags Source

Last extent in file.

efUnknown :: ExtentFlags Source

Data location unknown.

efDelalloc :: ExtentFlags Source

Location still pending.

efEncoded :: ExtentFlags Source

Data cannot be read while fs is unmounted.

efDataEncrypted :: ExtentFlags Source

Data is encrypted by fs.

efNotAligned :: ExtentFlags Source

Extent offsets may not be block aligned.

efDataInline :: ExtentFlags Source

Data mixed with metadata.

efDataTail :: ExtentFlags Source

Multiple files in block.

efUnwritten :: ExtentFlags Source

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

efMerged :: ExtentFlags Source

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

efShared :: ExtentFlags Source

Space shared with other files.

Extents

data Extent Source

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
Show Extent
Storable Extent

Request flags

data Flags Source

Request flags.

Constructors

Flags
Fields fSync :: Bool Sync the file before requesting its extents. fXattr :: Bool Retrieve the extents of the inode's extended attribute lookup tree, instead of its data tree.

Instances

Eq Flags
Show Flags

defaultFlags :: Flags Source

Default values for the request flags. Both fSync and fXattr are set to False.

Getting extent information

getExtentsFd Source

Arguments

:: Flags
-> 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 :: Flags -> FilePath -> Maybe (Word64, Word64) -> IO [Extent] Source

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

getExtentCountFd :: Flags -> Fd -> Maybe (Word64, Word64) -> IO Word32 Source

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

getExtentCount :: Flags -> FilePath -> Maybe (Word64, Word64) -> IO Word32 Source

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