XrdSys::KernelBuffer Class Reference

#include <XrdSysKernelBuffer.hh>

Public Member Functions
	KernelBuffer ()
	Default constructor.
	KernelBuffer (const KernelBuffer &)=delete
	Copy constructor - deleted.
	KernelBuffer (KernelBuffer &&kbuff)
KernelBuffer &	operator= (const KernelBuffer &)=delete
	Copy assignment operator - deleted.
KernelBuffer &	operator= (KernelBuffer &&kbuff)
	Move assignment operator.
	~KernelBuffer ()
	Destructor.
bool	Empty () const

Static Public Member Functions
static bool	IsPageAligned (const void *ptr)

Private Member Functions
void	Free ()
	Closes the underlying pipes (kernel buffers)
ssize_t	Alloc (size_t size)
	Allocates another pipe (kernel buffer) of size up to 1MB.
ssize_t	ReadFromFD (int fd, uint32_t length, int64_t *offset)
ssize_t	WriteToFD (int fd, int64_t *offset)
ssize_t	ToUser (char *&buffer)
ssize_t	FromUser (char *&buffer, size_t length)

Private Attributes
size_t	capacity
size_t	size
std::vector< std::tuple< std::array< int, 2 >, size_t > >	pipes
std::vector< std::tuple< std::array< int, 2 >, size_t > >::iterator	pipes_cursor

Static Private Attributes
static const size_t	PAGE_SZ = 4 * 1024
static const size_t	MAX_PIPE_SIZE = 1024 * 1024

Friends
ssize_t	Read (int, KernelBuffer &, uint32_t, int64_t)
ssize_t	Read (int, KernelBuffer &, uint32_t)
ssize_t	Write (int, KernelBuffer &, int64_t)
ssize_t	Send (int, KernelBuffer &)
ssize_t	Move (KernelBuffer &, char *&)
ssize_t	Move (char *&, KernelBuffer &, size_t)

Detailed Description

A utility class for manipulating kernel space buffers

(Encapsulates the splice vmsplice & syscalls.)

Constructor & Destructor Documentation

KernelBuffer() [1/3]

XrdSys::KernelBuffer::KernelBuffer ( )

inline

Default constructor.

KernelBuffer() [2/3]

XrdSys::KernelBuffer::KernelBuffer ( const KernelBuffer &  )

delete

Copy constructor - deleted.

KernelBuffer() [3/3]

XrdSys::KernelBuffer::KernelBuffer ( KernelBuffer &&  kbuff )

inline

References capacity, and size.

~KernelBuffer()

XrdSys::KernelBuffer::~KernelBuffer ( )

inline

Destructor.

References capacity, and Free().

Member Function Documentation

Alloc()

ssize_t XrdSys::KernelBuffer::Alloc ( size_t  size )

inlineprivate

Allocates another pipe (kernel buffer) of size up to 1MB.

References capacity, MAX_PIPE_SIZE, pipes, and size.

Referenced by FromUser().

Empty()

bool XrdSys::KernelBuffer::Empty ( ) const

inline

Returns

: true is buffer is empty, false otherwise

References size.

Free()

void XrdSys::KernelBuffer::Free ( )

inlineprivate

Closes the underlying pipes (kernel buffers)

References capacity, close, pipes, and size.

Referenced by FromUser(), ToUser(), and ~KernelBuffer().

FromUser()

ssize_t XrdSys::KernelBuffer::FromUser ( char *&  buffer, size_t  length  )

inlineprivate

Move a buffer from user space to kernel space

Parameters

buffer	: buffer to be moved to kernel space (needs to be page aligned and deallocable with free)
length	: length of the buffer

Returns

: number of bytes transferred to kernel space or -1 on error

NOTE: on success the user space buffer will be freed and the buffer will be set to NULL

NOTE: The user pages are a gift to the kernel. The application may not modify this memory ever, otherwise the page cache and on- disk data may differ.

References Alloc(), capacity, Free(), IsPageAligned(), pipes, pipes_cursor, and size.

IsPageAligned()

static bool XrdSys::KernelBuffer::IsPageAligned ( const void *  ptr )

inlinestatic

Check if the user space buffer is page aligned

Parameters

ptr	: user space buffer

Returns

: true if the buffer is page aligned, false otherwise

References PAGE_SZ.

Referenced by FromUser().

operator=() [1/2]

KernelBuffer & XrdSys::KernelBuffer::operator= ( const KernelBuffer &  )

delete

Copy assignment operator - deleted.

operator=() [2/2]

KernelBuffer & XrdSys::KernelBuffer::operator= ( KernelBuffer &&  kbuff )

inline

Move assignment operator.

References capacity, pipes, and size.

ReadFromFD()

ssize_t XrdSys::KernelBuffer::ReadFromFD ( int  fd, uint32_t  length, int64_t *  offset  )

inlineprivate

Read data from a file descriptor to a kernel buffer

Parameters

fd	: file descriptor
length	: amount of data to be read
offset	: offset of the data in the source file

Returns

: size of the data read from the file descriptor or -1 on error

ToUser()

ssize_t XrdSys::KernelBuffer::ToUser ( char *&  buffer )

inlineprivate

Move the buffer to user space:

Parameters

buffer

: a user space buffer containing the data, allocated by ToUser routine, to be deallocated with free()

Returns

: number of bytes transferred to user space or -1 on error

Note: vmsplice() really supports true splicing only from user memory to a pipe. In the opposite direction, it actually just copies the data to userspace. But this makes the interface nice and symmetric and enables people to build on vmsplice() with room for future improvement in performance.

References Free(), MAX_PIPE_SIZE, PAGE_SZ, pipes, pipes_cursor, and size.

WriteToFD()

ssize_t XrdSys::KernelBuffer::WriteToFD ( int  fd, int64_t *  offset  )

inlineprivate

Write data from a kernel buffer to a file descriptor

Parameters

fd	: file descriptor
offset	: offset in the target file

Returns

: size of the data written into the file descriptor or -1 on error

Friends And Related Symbol Documentation

Move [1/2]

ssize_t Move ( char *&  ubuff, KernelBuffer &  kbuff, size_t  length  )

friend

Utility function for moving a user space buffer to kernel space.

See also

KernelBuffer::FromUser

Move [2/2]

ssize_t Move ( KernelBuffer &  kbuff, char *&  ubuff  )

friend

Utility function for moving a kernel buffer to user space.

See also

KernelBuffer::ToUser

Read [1/2]

ssize_t Read ( int  fd, KernelBuffer &  buffer, uint32_t  length  )

friend

Utility function for reading data from a file descriptor into a kernel buffer.

See also

KernelBuffer::ReadFromFD

Read [2/2]

ssize_t Read ( int  fd, KernelBuffer &  buffer, uint32_t  length, int64_t  offset  )

friend

Utility function for reading data from a file descriptor into a kernel buffer.

See also

KernelBuffer::ReadFromFD

Send

ssize_t Send ( int  fd, KernelBuffer &  buffer  )

friend

Utility function for sending data from a kernel buffer into a socket.

See also

KernelBuffer::WriteToFD

Write

ssize_t Write ( int  fd, KernelBuffer &  buffer, int64_t  offset  )

friend

Utility function for writing data from a kernel buffer into a file descriptor.

See also

KernelBuffer::WriteToFD

Member Data Documentation

capacity

size_t XrdSys::KernelBuffer::capacity

private

Referenced by Alloc(), Free(), FromUser(), KernelBuffer(), operator=(), and ~KernelBuffer().

MAX_PIPE_SIZE

const size_t XrdSys::KernelBuffer::MAX_PIPE_SIZE = 1024 * 1024

staticprivate

Referenced by Alloc(), and ToUser().

PAGE_SZ

const size_t XrdSys::KernelBuffer::PAGE_SZ = 4 * 1024

staticprivate

Referenced by IsPageAligned(), and ToUser().

pipes

std::vector<std::tuple<std::array<int,2>, size_t> > XrdSys::KernelBuffer::pipes

private

Referenced by Alloc(), Free(), FromUser(), operator=(), and ToUser().

pipes_cursor

std::vector<std::tuple<std::array<int,2>,size_t>>::iterator XrdSys::KernelBuffer::pipes_cursor

private

Referenced by FromUser(), and ToUser().

size

size_t XrdSys::KernelBuffer::size

private

Referenced by Alloc(), Empty(), Free(), FromUser(), KernelBuffer(), operator=(), and ToUser().

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The documentation for this class was generated from the following file:

• XrdSysKernelBuffer.hh