System.Linux.FileExtents

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.

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

Show Extent

Storable Extent

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

Show ReqFlags

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.