mirror of
http://git.haproxy.org/git/haproxy.git/
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e0d0b4089d
Since last commit there's no point anymore in having two variants of the same function, let's switch to b_free() only. __b_drop() was renamed to __b_free() for obvious consistency reasons.
679 lines
43 KiB
Plaintext
679 lines
43 KiB
Plaintext
2018-07-13 - HAProxy Internal Buffer API
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1. Background
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HAProxy uses a "struct buffer" internally to store data received from external
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agents, as well as data to be sent to external agents. These buffers are also
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used during data transformation such as compression, header insertion or
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defragmentation, and are used to carry intermediary representations between the
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various internal layers. They support wrapping at the end, and they carry their
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own size information so that in theory it would be possible to use different
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buffer sizes in parallel eventhough this is not currently implemented.
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The format of this structure has evolved over time, to reach a point where it
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is convenient and versatile enough to have permitted to make several internal
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types converge into a single one (specifically the struct chunk disappeared).
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2. Representation as of 1.9-dev1
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The current buffer representation consists in a linear storage area of known
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size, with a head position indicating the oldest data, and a total data count
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expressed in bytes. The head position, data count and size are expressed as
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integers and are positive or null. By convention, the head position is strictly
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smaller than the buffer size and the data count is smaller than or equal to the
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size, so that wrapping can be resolved with a single subtract. A buffer not
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respecting these rules is said to be degenerate. Unless specified otherwise,
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the various API functions will adopt an undefined behaviour when passed such a
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degenerate buffer.
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Buffer declaration :
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struct buffer {
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size_t size; // size of the storage area (wrapping point)
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char *area; // start of the storage area
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size_t data; // contents length after head
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size_t head; // start offset of remaining data relative to area
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};
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Linear buffer representation :
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area
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V<--------------------------------------------------------->| size
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+-----------+---------------------------------+-------------+
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| |/////////////////////////////////| |
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+-----------+---------------------------------+-------------+
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|<--------->|<------------------------------->|
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head data ^
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tail
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Wrapping buffer representation :
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area
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V<--------------------------------------------------------->| size
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+---------------+------------------------+------------------+
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|///////////////| |//////////////////|
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+---------------+------------------------+------------------+
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|<-------------------------------------->| head
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|-------------->| ...data data...|<-----------------|
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^
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tail
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3. Terminology
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Manipulating a buffer just based on a head and a wrapping data count is not
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very convenient, so we define a certain number of terms for important elements
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characterizing a buffer :
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- origin : pointer to relative position 0 in the storage area. Undefined
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when the buffer is not allocated.
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- size : the allocated size of the storage area starting at the origin,
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expressed in bytes. A buffer whose size is zero is said not to
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be allocated, and its origin in this case is undefined.
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- data : the amount of data the buffer contains, in bytes. It is always
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lower than or equal to the buffer's size, hence it is always 0
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for an unallocated buffer.
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- emptiness : a buffer is said to be empty when it contains no data, hence
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data == 0. It is possible for such buffers not to be allocated
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and to have size == 0 as well.
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- room : the available space in the buffer. This is its size minus data.
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- head : position relative to origin where the oldest data byte is found
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(it typically is what send() uses to pick outgoing data). The
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head is strictly smaller than the size.
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- tail : position relative to origin where the first spare byte is found
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(it typically is what recv() uses to store incoming data). It
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is always equal to the buffer's data added to its head modulo
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the buffer's size.
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- wrapping : the byte following the last one of the storage area loops back
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to position 0. This is called wrapping. The wrapping point is
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the first position relative to origin which doesn't belong to
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the storage area. There is no wrapping when a buffer is not
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allocated. Wrapping requires special care and means that the
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regular string manipulation functions are not usable on most
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buffers, unless it is known that no wrapping happens. Free
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space may wrap as well if the buffer only contains data in the
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middle.
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- alignment : a buffer is said to be aligned if its data do not wrap. That
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is, its head is strictly before the tail, or the buffer is
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empty and the head is null. Aligning a buffer may be required
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to use regular string manipulation functions which have no
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support for wrapping.
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A buffer may be in three different states :
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- unallocated : size == 0, area == 0 (b_is_null() is true)
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- waiting : size == 0, area != 0
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- allocated : size > 0, area > 0
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It is not permitted to have area == 0 with a non-null size. In addition, the
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waiting state may also be used to indicate a read-only buffer which does not
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wrap and which must not be freed (e.g. for use with error messages).
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The basic API only covers allocated buffers. Switching to/from the other states
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is covered by the management API since it requires specific allocation and free
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calls.
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4. Using buffers
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Buffers are defined in a few files :
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- include/common/buf.h : structure definition, and manipulation functions
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- include/common/buffer.h : resource management (alloc/free/wait lists)
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- include/common/istbuf.h : advanced string manipulation
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4.1. Basic API
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The basic API is made of the functions which abstract accesses to the buffers
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and which help calculating their state, free space or used space.
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====================+==================+=======================================
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Function | Arguments/Return | Description
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--------------------+------------------+---------------------------------------
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b_is_null() | const buffer *buf| returns true if (and only if) the
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| ret: int | buffer is not yet allocated and thus
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| | points to a NULL area
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--------------------+------------------+---------------------------------------
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b_orig() | const buffer *buf| returns the pointer to the origin of
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| ret: char * | the storage, which is the location of
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| | byte at offset zero. This is mostly
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| | used by functions which handle the
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| | wrapping by themselves
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--------------------+------------------+---------------------------------------
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b_size() | const buffer *buf| returns the size of the buffer
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| ret: size_t |
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--------------------+------------------+---------------------------------------
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b_wrap() | const buffer *buf| returns the pointer to the wrapping
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| ret: char * | position of the buffer area, which is
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| | by definition the first byte not part
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| | of the buffer
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--------------------+------------------+---------------------------------------
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b_data() | const buffer *buf| returns the number of bytes present in
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| ret: size_t | the buffer
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--------------------+------------------+---------------------------------------
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b_room() | const buffer *buf| returns the amount of room left in the
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| ret: size_t | buffer
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--------------------+------------------+---------------------------------------
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b_full() | const buffer *buf| returns true if the buffer is full
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| ret: int |
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--------------------+------------------+---------------------------------------
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__b_stop() | const buffer *buf| returns a pointer to the byte
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| ret: char * | following the end of the buffer, which
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| | may be out of the buffer if the buffer
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| | ends on the last byte of the area. It
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| | is the caller's responsibility to
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| | either know that the buffer does not
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| | wrap or to check that the result does
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| | not wrap
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--------------------+------------------+---------------------------------------
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__b_stop_ofs() | const buffer *buf| returns an origin-relative offset
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| ret: size_t | pointing to the byte following the end
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| | of the buffer, which may be out of the
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| | buffer if the buffer ends on the last
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| | byte of the area. It's the caller's
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| | responsibility to either know that the
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| | buffer does not wrap or to check that
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| | the result does not wrap
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--------------------+------------------+---------------------------------------
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b_stop() | const buffer *buf| returns the pointer to the byte
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| ret: char * | following the end of the buffer, which
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| | may be out of the buffer if the buffer
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| | ends on the last byte of the area
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--------------------+------------------+---------------------------------------
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b_stop_ofs() | const buffer *buf| returns an origin-relative offset
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| ret: size_t | pointing to the byte following the end
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| | of the buffer, which may be out of the
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| | buffer if the buffer ends on the last
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| | byte of the area
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--------------------+------------------+---------------------------------------
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__b_peek() | const buffer *buf| returns a pointer to the data at
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| size_t ofs | position <ofs> relative to the head of
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| ret: char * | the buffer. Will typically point to
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| | input data if called with the amount
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| | of output data. It's the caller's
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| | responsibility to either know that the
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| | buffer does not wrap or to check that
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| | the result does not wrap
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--------------------+------------------+---------------------------------------
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__b_peek_ofs() | const buffer *buf| returns an origin-relative offset
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| size_t ofs | pointing to the data at position <ofs>
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| ret: size_t | relative to the head of the
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| | buffer. Will typically point to input
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| | data if called with the amount of
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| | output data. It's the caller's
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| | responsibility to either know that the
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| | buffer does not wrap or to check that
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| | the result does not wrap
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--------------------+------------------+---------------------------------------
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b_peek() | const buffer *buf| returns a pointer to the data at
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| size_t ofs | position <ofs> relative to the head of
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| ret: char * | the buffer. Will typically point to
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| | input data if called with the amount
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| | of output data. If applying <ofs> to
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| | the buffers' head results in a
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| | position between <size> and 2*>size>-1
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| | included, a wrapping compensation is
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| | applied to the result
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--------------------+------------------+---------------------------------------
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b_peek_ofs() | const buffer *buf| returns an origin-relative offset
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| size_t ofs | pointing to the data at position <ofs>
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| ret: size_t | relative to the head of the
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| | buffer. Will typically point to input
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| | data if called with the amount of
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| | output data. If applying <ofs> to the
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| | buffers' head results in a position
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| | between <size> and 2*>size>-1
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| | included, a wrapping compensation is
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| | applied to the result
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--------------------+------------------+---------------------------------------
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__b_head() | const buffer *buf| returns the pointer to the buffer's
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| ret: char * | head, which is the location of the
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| | next byte to be dequeued. The result
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| | is undefined for unallocated buffers
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--------------------+------------------+---------------------------------------
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__b_head_ofs() | const buffer *buf| returns an origin-relative offset
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| ret: size_t | pointing to the buffer's head, which
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| | is the location of the next byte to be
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| | dequeued. The result is undefined for
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| | unallocated buffers
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--------------------+------------------+---------------------------------------
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b_head() | const buffer *buf| returns the pointer to the buffer's
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| ret: char * | head, which is the location of the
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| | next byte to be dequeued. The result
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| | is undefined for unallocated
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| | buffers. If applying <ofs> to the
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| | buffers' head results in a position
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| | between <size> and 2*>size>-1
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| | included, a wrapping compensation is
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| | applied to the result
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--------------------+------------------+---------------------------------------
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b_head_ofs() | const buffer *buf| returns an origin-relative offset
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| ret: size_t | pointing to the buffer's head, which
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| | is the location of the next byte to be
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| | dequeued. The result is undefined for
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| | unallocated buffers. If applying
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| | <ofs> to the buffers' head results in
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| | a position between <size> and
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| | 2*>size>-1 included, a wrapping
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| | compensation is applied to the result
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--------------------+------------------+---------------------------------------
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__b_tail() | const buffer *buf| returns the pointer to the tail of the
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| ret: char * | buffer, which is the location of the
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| | first byte where it is possible to
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| | enqueue new data. The result is
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| | undefined for unallocated buffers
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--------------------+------------------+---------------------------------------
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__b_tail_ofs() | const buffer *buf| returns an origin-relative offset
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| ret: size_t | pointing to the tail of the buffer,
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| | which is the location of the first
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| | byte where it is possible to enqueue
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| | new data. The result is undefined for
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| | unallocated buffers
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--------------------+------------------+---------------------------------------
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b_tail() | const buffer *buf| returns the pointer to the tail of the
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| ret: char * | buffer, which is the location of the
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| | first byte where it is possible to
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| | enqueue new data. The result is
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| | undefined for unallocated buffers
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--------------------+------------------+---------------------------------------
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b_tail_ofs() | const buffer *buf| returns an origin-relative offset
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| ret: size_t | pointing to the tail of the buffer,
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| | which is the location of the first
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| | byte where it is possible to enqueue
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| | new data. The result is undefined for
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| | unallocated buffers
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--------------------+------------------+---------------------------------------
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b_next() | const buffer *buf| for an absolute pointer <p> pointing
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| const char *p | to a valid location within buffer <b>,
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| ret: char * | returns the absolute pointer to the
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| | next byte, which usually is at (p + 1)
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| | unless p reaches the wrapping point
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| | and wrapping is needed
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--------------------+------------------+---------------------------------------
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b_next_ofs() | const buffer *buf| for an origin-relative offset <o>
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| size_t o | pointing to a valid location within
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| ret: size_t | buffer <b>, returns either the
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| | relative offset pointing to the next
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| | byte, which usually is at (o + 1)
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| | unless o reaches the wrapping point
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| | and wrapping is needed
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--------------------+------------------+---------------------------------------
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b_dist() | const buffer *buf| returns the distance between two
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| const char *from | pointers, taking into account the
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| const char *to | ability to wrap around the buffer's
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| ret: size_t | end. The operation is not defined if
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| | either of the pointers does not belong
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| | to the buffer or if their distance is
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| | greater than the buffer's size
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--------------------+------------------+---------------------------------------
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b_almost_full() | const buffer *buf| returns 1 if the buffer uses at least
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| ret: int | 3/4 of its capacity, otherwise
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| | zero. Buffers of size zero are
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| | considered full
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--------------------+------------------+---------------------------------------
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b_space_wraps() | const buffer *buf| returns non-zero only if the buffer's
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| ret: int | free space wraps, which means that the
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| | buffer contains data that are not
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| | touching at least one edge
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--------------------+------------------+---------------------------------------
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b_contig_data() | const buffer *buf| returns the amount of data that can
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| size_t start | contiguously be read at once starting
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| ret: size_t | from a relative offset <start> (which
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| | allows to easily pre-compute blocks
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| | for memcpy). The start point will
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| | typically contain the amount of past
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| | data already returned by a previous
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| | call to this function
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--------------------+------------------+---------------------------------------
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b_contig_space() | const buffer *buf| returns the amount of bytes that can
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| ret: size_t | be appended to the buffer at once
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--------------------+------------------+---------------------------------------
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b_getblk() | const buffer *buf| gets one full block of data at once
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| char *blk | from a buffer, starting from offset
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| size_t len | <offset> after the buffer's head, and
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| size_t offset | limited to no more than <len> bytes.
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| ret: size_t | The caller is responsible for ensuring
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| | that neither <offset> nor <offset> +
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| | <len> exceed the total number of bytes
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| | available in the buffer. Return zero
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| | if not enough data was available, in
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| | which case blk is left undefined, or
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| | the number of bytes read which is
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| | equal to the requested size
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--------------------+------------------+---------------------------------------
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b_getblk_nc() | const buffer *buf| gets one or two blocks of data at once
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| const char **blk1| from a buffer, starting from offset
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| size_t *len1 | <ofs> after the beginning of its
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| const char **blk2| output, and limited to no more than
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| size_t *len2 | <max> bytes. The caller is responsible
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| size_t ofs | for ensuring that neither <ofs> nor
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| size_t max | <ofs>+<max> exceed the total number of
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| ret: int | bytes available in the buffer. Returns
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| | 0 if not enough data were available,
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| | or the number of blocks filled (1 or
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| | 2). <blk1> is always filled before
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| | <blk2>. The unused blocks are left
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| | undefined, and the buffer is left
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| | unaffected. Unused buffers are left in
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| | an undefined state
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--------------------+------------------+---------------------------------------
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b_reset() | buffer *buf | resets a buffer. The size is not
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| ret: void | touched. In practice it resets the
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| | head and the data length
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--------------------+------------------+---------------------------------------
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b_sub() | buffer *buf | decreases the buffer length by <count>
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| size_t count | without touching the head position
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| ret: void | (only the tail moves). this may mostly
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| | be used to trim pending data before
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| | reusing a buffer. The caller is
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| | responsible for not removing more than
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| | the available data
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--------------------+------------------+---------------------------------------
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b_add() | buffer *buf | increase the buffer length by <count>
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| size_t count | without touching the head position
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| ret: void | (only the tail moves). This is used
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| | when adding data at the tail of a
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| | buffer. The caller is responsible for
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| | not adding more than the available
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| | room
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--------------------+------------------+---------------------------------------
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b_set_data() | buffer *buf | sets the buffer's length, by adjusting
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| size_t len | the buffer's tail only. The caller is
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| ret: void | responsible for passing a valid length
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--------------------+------------------+---------------------------------------
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b_del() | buffer *buf | deletes <del> bytes at the head of
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| size_t del | buffer <b> and updates the head. The
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| ret: void | caller is responsible for not removing
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| | more than the available data. This is
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| | used after sending data from the
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| | buffer
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--------------------+------------------+---------------------------------------
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b_realign_if_empty()| buffer *buf | realigns a buffer if it's empty, does
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| ret: void | nothing otherwise. This is mostly used
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| | after b_del() to make an empty
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| | buffer's free space contiguous
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--------------------+------------------+---------------------------------------
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b_slow_realign() | buffer *buf | realigns a possibly wrapping buffer so
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| size_t output | that the part remaining to be parsed
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| ret: void | is contiguous and starts at the
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| | beginning of the buffer and the
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| | already parsed output part ends at the
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| | end of the buffer. This provides the
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| | best conditions since it allows the
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| | largest inputs to be processed at once
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| | and ensures that once the output data
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| | leaves, the whole buffer is available
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| | at once. The number of output bytes
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| | supposedly present at the beginning of
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| | the buffer and which need to be moved
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| | to the end must be passed in <output>.
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| | It will effectively make this offset
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| | the new wrapping point. A temporary
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| | swap area at least as large as b->size
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| | must be provided in <swap>. It's up
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| | to the caller to ensure <output> is no
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| | larger than the difference between the
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| | whole buffer's length and its input
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--------------------+------------------+---------------------------------------
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b_putchar() | buffer *buf | tries to append char <c> at the end of
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| char c | buffer <b>. Supports wrapping. New
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| ret: void | data are silently discarded if the
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| | buffer is already full
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--------------------+------------------+---------------------------------------
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b_putblk() | buffer *buf | tries to append block <blk> at the end
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| const char *blk | of buffer <b>. Supports wrapping. Data
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| size_t len | are truncated if the buffer is too
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| ret: size_t | short or if not enough space is
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| | available. It returns the number of
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| | bytes really copied
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--------------------+------------------+---------------------------------------
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b_move() | buffer *buf | moves block (src,len) left or right
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| size_t src | by <shift> bytes, supporting wrapping
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| size_t len | and overlapping.
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| size_t shift |
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--------------------+------------------+---------------------------------------
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b_rep_blk() | buffer *buf | writes the block <blk> at position
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| char *pos | <pos> which must be in buffer <b>, and
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| char *end | moves the part between <end> and the
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| const char *blk | buffer's tail just after the end of
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| size_t len | the copy of <blk>. This effectively
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| ret: int | replaces the part located between
|
|
| | <pos> and <end> with a copy of <blk>
|
|
| | of length <len>. The buffer's length
|
|
| | is automatically updated. This is used
|
|
| | to replace a block with another one
|
|
| | inside a buffer. The shift value
|
|
| | (positive or negative) is returned. If
|
|
| | there's no space left, the move is not
|
|
| | done. If <len> is null, the <blk>
|
|
| | pointer is allowed to be null, in
|
|
| | order to erase a block
|
|
--------------------+------------------+---------------------------------------
|
|
b_xfer() | buffer *src | transfers at most <count> bytes from
|
|
| buffer *dst | buffer <src> to buffer <dst> and
|
|
| size_t cout | returns the number of bytes copied.
|
|
| ret: size_t | The bytes are removed from <src> and
|
|
| | added to <dst>. The caller guarantees
|
|
| | that <count> is <= b_room(dst)
|
|
====================+==================+=======================================
|
|
|
|
|
|
4.2. String API
|
|
|
|
The string API aims at providing both convenient and efficient ways to read and
|
|
write to/from buffers using indirect strings (ist). These strings and some
|
|
associated functions are defined in ist.h.
|
|
|
|
====================+==================+=======================================
|
|
Function | Arguments/Return | Description
|
|
--------------------+------------------+---------------------------------------
|
|
b_isteq() | const buffer *b | b_isteq() : returns > 0 if the first
|
|
| size_t o | <n> characters of buffer <b> starting
|
|
| size_t n | at offset <o> relative to the buffer's
|
|
| const ist ist | head match <ist>. (empty strings do
|
|
| ret: int | match). It is designed to be used with
|
|
| | reasonably small strings (it matches a
|
|
| | single byte per loop iteration). It is
|
|
| | expected to be used with an offset to
|
|
| | skip old data. Return value number of
|
|
| | matching bytes if >0, not enough bytes
|
|
| | or empty string if 0, or non-matching
|
|
| | byte found if <0.
|
|
--------------------+------------------+---------------------------------------
|
|
b_isteat | struct buffer *b | b_isteat() : "eats" string <ist> from
|
|
| const ist ist | the head of buffer <b>. Wrapping data
|
|
| ret: ssize_t | is explicitly supported. It matches a
|
|
| | single byte per iteration so strings
|
|
| | should remain reasonably small.
|
|
| | Returns the number of bytes matched
|
|
| | and eaten if >0, not enough bytes or
|
|
| | matched empty string if 0, or non
|
|
| | matching byte found if <0.
|
|
--------------------+------------------+---------------------------------------
|
|
b_istput | struct buffer *b | b_istput() : injects string <ist> at
|
|
| const ist ist | the tail of output buffer <b> provided
|
|
| ret: ssize_t | that it fits. Wrapping is supported.
|
|
| | It's designed for small strings as it
|
|
| | only writes a single byte per
|
|
| | iteration. Returns the number of
|
|
| | characters copied (ist.len), 0 if it
|
|
| | temporarily does not fit, or -1 if it
|
|
| | will never fit. It will only modify
|
|
| | the buffer upon success. In all cases,
|
|
| | the contents are copied prior to
|
|
| | reporting an error, so that the
|
|
| | destination at least contains a valid
|
|
| | but truncated string.
|
|
--------------------+------------------+---------------------------------------
|
|
b_putist | struct buffer *b | b_putist() : tries to copy as much as
|
|
| const ist ist | possible of string <ist> into buffer
|
|
| ret: size_t | <b> and returns the number of bytes
|
|
| | copied (truncation is possible). It
|
|
| | uses b_putblk() and is suitable for
|
|
| | large blocks.
|
|
====================+==================+=======================================
|
|
|
|
|
|
4.3. Management API
|
|
|
|
The management API makes a distinction between an empty buffer, which by
|
|
definition is not allocated but is ready to be allocated at any time, and a
|
|
buffer which failed an allocation and is waiting for an available area to be
|
|
offered. The functions allow to register on a list to be notified about buffer
|
|
availability, to notify others of a number of buffers just released, and to be
|
|
and to be notified of buffer availability. All allocations are made through the
|
|
standard buffer pools.
|
|
|
|
====================+==================+=======================================
|
|
Function | Arguments/Return | Description
|
|
--------------------+------------------+---------------------------------------
|
|
buffer_almost_full | const buffer *buf| returns true if the buffer is not null
|
|
| ret: int | and at least 3/4 of the buffer's space
|
|
| | are used. A waiting buffer will match.
|
|
--------------------+------------------+---------------------------------------
|
|
b_alloc | buffer *buf | allocates a buffer and assigns it to
|
|
| ret: buffer * | *buf. If no memory is available, (1)
|
|
| | is assigned instead with a zero size.
|
|
| | No control is made to check if *buf
|
|
| | already pointed to another buffer. The
|
|
| | allocated buffer is returned, or NULL
|
|
| | in case no memory is available
|
|
--------------------+------------------+---------------------------------------
|
|
b_alloc_fast | buffer *buf | allocates a buffer and assigns it to
|
|
| ret: buffer * | *buf. If no memory is available, (1)
|
|
| | is assigned instead with a zero size.
|
|
| | No control is made to check if *buf
|
|
| | already pointed to another buffer. The
|
|
| | allocated buffer is returned, or NULL
|
|
| | in case no memory is available. The
|
|
| | difference with b_alloc() is that this
|
|
| | function only picks from the pool and
|
|
| | never calls malloc(), so it can fail
|
|
| | even if some memory is available
|
|
--------------------+------------------+---------------------------------------
|
|
__b_free | buffer *buf | releases <buf> which must be allocated
|
|
| ret: void | and marks it empty
|
|
--------------------+------------------+---------------------------------------
|
|
b_free | buffer *buf | releases <buf> only if it is allocated
|
|
| ret: void | and marks it empty
|
|
--------------------+------------------+---------------------------------------
|
|
b_alloc_margin | buffer *buf | ensures that <buf> is allocated. If an
|
|
| int margin | allocation is needed, it ensures that
|
|
| ret: buffer * | there are still at least <margin>
|
|
| | buffers available in the pool after
|
|
| | this allocation so that we don't leave
|
|
| | the pool in a condition where a
|
|
| | session or a response buffer could not
|
|
| | be allocated anymore, resulting in a
|
|
| | deadlock. This means that we sometimes
|
|
| | need to try to allocate extra entries
|
|
| | even if only one buffer is needed
|
|
--------------------+------------------+---------------------------------------
|
|
offer_buffers() | void *from | offer a buffer currently belonging to
|
|
| uint threshold | target <from> to whoever needs
|
|
| ret: void | one. Any pointer is valid for <from>,
|
|
| | including NULL. Its purpose is to
|
|
| | avoid passing a buffer to oneself in
|
|
| | case of failed allocations (e.g. need
|
|
| | two buffers, get one, fail, release it
|
|
| | and wake up self again). In case of
|
|
| | normal buffer release where it is
|
|
| | expected that the caller is not
|
|
| | waiting for a buffer, NULL is fine
|
|
====================+==================+=======================================
|
|
|
|
|
|
5. Porting code from older versions
|
|
|
|
The previous buffer API introduced in 1.5-dev9 (May 2012) used to look like the
|
|
following (with the struct renamed to old_buffer here to avoid confusion during
|
|
quick lookups at the doc). It's worth noting that the "data" field used to be
|
|
part of the struct but with a different type and meaning. It's important to be
|
|
careful about potential code making use of &b->data as it will silently compile
|
|
but fail.
|
|
|
|
Previous buffer declaration :
|
|
|
|
struct old_buffer {
|
|
char *p; /* buffer's start pointer, separates in and out data */
|
|
unsigned int size; /* buffer size in bytes */
|
|
unsigned int i; /* number of input bytes pending for analysis in the buffer */
|
|
unsigned int o; /* number of out bytes the sender can consume from this buffer */
|
|
char data[0]; /* <size> bytes */
|
|
};
|
|
|
|
Previous linear buffer representation :
|
|
|
|
data p
|
|
| |
|
|
V V
|
|
+-----------+--------------------+------------+-------------+
|
|
| |////////////////////|////////////| |
|
|
+-----------+--------------------+------------+-------------+
|
|
<---------------------------------------------------------> size
|
|
<------------------> <---------->
|
|
o i
|
|
|
|
There is this correspondance between old and new fields (some will involve a
|
|
knowledge of a channel when the output byte count is required) :
|
|
|
|
Old | New
|
|
--------+----------------------------------------------------
|
|
p | data + head + co_data(channel) // ci_head(channel)
|
|
size | size
|
|
i | data - co_data(channel) // ci_data(channel)
|
|
o | co_data(channel) // channel->output
|
|
data | area
|
|
--------+-----------------------------------------------------
|
|
|
|
Then some common expressions can be mapped like this :
|
|
|
|
Old | New
|
|
-----------------------+---------------------------------------
|
|
b->data | b_orig(b)
|
|
&b->data | b_orig(b)
|
|
bi_ptr(b) | ci_head(channel)
|
|
bi_end(b) | b_tail(b)
|
|
bo_ptr(b) | b_head(b)
|
|
bo_end(b) | co_tail(channel)
|
|
bi_putblk(b,s,l) | b_putblk(b,s,l)
|
|
bo_getblk(b,s,l,o) | b_getblk(b,s,l,o)
|
|
bo_getblk_nc(b,s,l,o) | b_getblk_nc(b,s,l,o,0,co_data(channel))
|
|
b->i + b->o | b_data(b)
|
|
b->data + b->size | b_wrap(b)
|
|
b->i += len | b_add(b, len)
|
|
b->i -= len | b_sub(b, len)
|
|
b->i = len | b_set_data(b, co_data(channel) + len)
|
|
b->o += len | b_add(b, len); channel->output += len
|
|
b->o -= len | b_del(b, len); channel->output -= len
|
|
-----------------------+---------------------------------------
|
|
|
|
The buffer modification functions are less straightforward and depend a lot on
|
|
the context where they are used. It is strongly advised to figure in the list
|
|
of functions above what is available based on what is attempted to be done in
|
|
the existing code.
|
|
|
|
Note that it is very likely that any out-of-tree code relying on buffers will
|
|
not use both ->i and ->o but instead will use exclusively ->i on the side
|
|
producing data and use exclusively ->o on the side consuming data (such as in a
|
|
mux or in an applet). In both cases, it should be assumed that the other side
|
|
is always zero and that either ->i or ->o is replaced with ->data, making the
|
|
remaining code much simpler (no more code duplication based on the data
|
|
direction).
|