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8. Resources

8.1 Introduction

Most large software projects implemented in classical procedural programming languages usually end up with lots of code taking care of resource allocation and deallocation. Bugs in such code are often very difficult to find, because they cause only `resource leakage', that is keeping a lot of memory and other resources which nobody references to.

We've tried to solve this problem by employing a resource tracking system which keeps track of all the resources allocated by all the modules of BIRD, deallocates everything automatically when a module shuts down and it is able to print out the list of resources and the corresponding modules they are allocated by.

Each allocated resource (from now we'll speak about allocated resources only) is represented by a structure starting with a standard header (struct resource) consisting of a list node (resources are often linked to various lists) and a pointer to resclass -- a resource class structure pointing to functions implementing generic resource operations (such as freeing of the resource) for the particular resource type.

There exist the following types of resources:

8.2 Resource pools

Resource pools (pool) are just containers holding a list of other resources. Freeing a pool causes all the listed resources to be freed as well. Each existing resource is linked to some pool except for a root pool which isn't linked anywhere, so all the resources form a tree structure with internal nodes corresponding to pools and leaves being the other resources.

Example: Almost all modules of BIRD have their private pool which is freed upon shutdown of the module.


Function

pool * rp_new (pool * p, const char * name) -- create a resource pool

Arguments

pool * p

parent pool

const char * name

pool name (to be included in debugging dumps)

Description

rp_new() creates a new resource pool inside the specified parent pool.


Function

void rmove (void * res, pool * p) -- move a resource

Arguments

void * res

resource

pool * p

pool to move the resource to

Description

rmove() moves a resource from one pool to another.


Function

void rfree (void * res) -- free a resource

Arguments

void * res

resource

Description

rfree() frees the given resource and all information associated with it. In case it's a resource pool, it also frees all the objects living inside the pool.

It works by calling a class-specific freeing function.


Function

void rdump (void * res) -- dump a resource

Arguments

void * res

resource

Description

This function prints out all available information about the given resource to the debugging output.

It works by calling a class-specific dump function.


Function

void * ralloc (pool * p, struct resclass * c) -- create a resource

Arguments

pool * p

pool to create the resource in

struct resclass * c

class of the new resource

Description

This function is called by the resource classes to create a new resource of the specified class and link it to the given pool. Allocated memory is zeroed. Size of the resource structure is taken from the size field of the resclass.


Function

void rlookup (unsigned long a) -- look up a memory location

Arguments

unsigned long a

memory address

Description

This function examines all existing resources to see whether the address a is inside any resource. It's used for debugging purposes only.

It works by calling a class-specific lookup function for each resource.


Function

void resource_init (void) -- initialize the resource manager

Description

This function is called during BIRD startup. It initializes all data structures of the resource manager and creates the root pool.

8.3 Memory blocks

Memory blocks are pieces of contiguous allocated memory. They are a bit non-standard since they are represented not by a pointer to resource, but by a void pointer to the start of data of the memory block. All memory block functions know how to locate the header given the data pointer.

Example: All "unique" data structures such as hash tables are allocated as memory blocks.


Function

void * mb_alloc (pool * p, unsigned size) -- allocate a memory block

Arguments

pool * p

pool

unsigned size

size of the block

Description

mb_alloc() allocates memory of a given size and creates a memory block resource representing this memory chunk in the pool p.

Please note that mb_alloc() returns a pointer to the memory chunk, not to the resource, hence you have to free it using mb_free(), not rfree().


Function

void * mb_allocz (pool * p, unsigned size) -- allocate and clear a memory block

Arguments

pool * p

pool

unsigned size

size of the block

Description

mb_allocz() allocates memory of a given size, initializes it to zeroes and creates a memory block resource representing this memory chunk in the pool p.

Please note that mb_allocz() returns a pointer to the memory chunk, not to the resource, hence you have to free it using mb_free(), not rfree().


Function

void * mb_realloc (void * m, unsigned size) -- reallocate a memory block

Arguments

void * m

memory block

unsigned size

new size of the block

Description

mb_realloc() changes the size of the memory block m to a given size. The contents will be unchanged to the minimum of the old and new sizes; newly allocated memory will be uninitialized. Contrary to realloc() behavior, m must be non-NULL, because the resource pool is inherited from it.

Like mb_alloc(), mb_realloc() also returns a pointer to the memory chunk, not to the resource, hence you have to free it using mb_free(), not rfree().


Function

void mb_free (void * m) -- free a memory block

Arguments

void * m

memory block

Description

mb_free() frees all memory associated with the block m.

8.4 Linear memory pools

Linear memory pools are collections of memory blocks which support very fast allocation of new blocks, but are able to free only the whole collection at once (or in stack order).

Example: Each configuration is described by a complex system of structures, linked lists and function trees which are all allocated from a single linear pool, thus they can be freed at once when the configuration is no longer used.


Function

linpool * lp_new (pool * p, uint blk) -- create a new linear memory pool

Arguments

pool * p

pool

uint blk

block size

Description

lp_new() creates a new linear memory pool resource inside the pool p. The linear pool consists of a list of memory chunks of size at least blk.


Function

void * lp_alloc (linpool * m, uint size) -- allocate memory from a linpool

Arguments

linpool * m

linear memory pool

uint size

amount of memory

Description

lp_alloc() allocates size bytes of memory from a linpool m and it returns a pointer to the allocated memory.

It works by trying to find free space in the last memory chunk associated with the linpool and creating a new chunk of the standard size (as specified during lp_new()) if the free space is too small to satisfy the allocation. If size is too large to fit in a standard size chunk, an "overflow" chunk is created for it instead.


Function

void * lp_allocu (linpool * m, uint size) -- allocate unaligned memory from a linpool

Arguments

linpool * m

linear memory pool

uint size

amount of memory

Description

lp_allocu() allocates size bytes of memory from a linpool m and it returns a pointer to the allocated memory. It doesn't attempt to align the memory block, giving a very efficient way how to allocate strings without any space overhead.


Function

void * lp_allocz (linpool * m, uint size) -- allocate cleared memory from a linpool

Arguments

linpool * m

linear memory pool

uint size

amount of memory

Description

This function is identical to lp_alloc() except that it clears the allocated memory block.


Function

void lp_flush (linpool * m) -- flush a linear memory pool

Arguments

linpool * m

linear memory pool

Description

This function frees the whole contents of the given linpool m, but leaves the pool itself.


Function

void lp_save (linpool * m, lp_state * p) -- save the state of a linear memory pool

Arguments

linpool * m

linear memory pool

lp_state * p

state buffer

Description

This function saves the state of a linear memory pool. Saved state can be used later to restore the pool (to free memory allocated since).


Function

void lp_restore (linpool * m, lp_state * p) -- restore the state of a linear memory pool

Arguments

linpool * m

linear memory pool

lp_state * p

saved state

Description

This function restores the state of a linear memory pool, freeing all memory allocated since the state was saved. Note that the function cannot un-free the memory, therefore the function also invalidates other states that were saved between (on the same pool).

8.5 Slabs

Slabs are collections of memory blocks of a fixed size. They support very fast allocation and freeing of such blocks, prevent memory fragmentation and optimize L2 cache usage. Slabs have been invented by Jeff Bonwick and published in USENIX proceedings as `The Slab Allocator: An Object-Caching Kernel Memory Allocator'. Our implementation follows this article except that we don't use constructors and destructors.

When the DEBUGGING switch is turned on, we automatically fill all newly allocated and freed blocks with a special pattern to make detection of use of uninitialized or already freed memory easier.

Example: Nodes of a FIB are allocated from a per-FIB Slab.


Function

slab * sl_new (pool * p, uint size) -- create a new Slab

Arguments

pool * p

resource pool

uint size

block size

Description

This function creates a new Slab resource from which objects of size size can be allocated.


Function

void * sl_alloc (slab * s) -- allocate an object from Slab

Arguments

slab * s

slab

Description

sl_alloc() allocates space for a single object from the Slab and returns a pointer to the object.


Function

void sl_free (slab * s, void * oo) -- return a free object back to a Slab

Arguments

slab * s

slab

void * oo

object returned by sl_alloc()

Description

This function frees memory associated with the object oo and returns it back to the Slab s.

8.6 Events

Events are there to keep track of deferred execution. Since BIRD is single-threaded, it requires long lasting tasks to be split to smaller parts, so that no module can monopolize the CPU. To split such a task, just create an event resource, point it to the function you want to have called and call ev_schedule() to ask the core to run the event when nothing more important requires attention.

You can also define your own event lists (the event_list structure), enqueue your events in them and explicitly ask to run them.


Function

event * ev_new (pool * p) -- create a new event

Arguments

pool * p

resource pool

Description

This function creates a new event resource. To use it, you need to fill the structure fields and call ev_schedule().


Function

void ev_run (event * e) -- run an event

Arguments

event * e

an event

Description

This function explicitly runs the event e (calls its hook function) and removes it from an event list if it's linked to any.

From the hook function, you can call ev_enqueue() or ev_schedule() to re-add the event.


Function

void ev_enqueue (event_list * l, event * e) -- enqueue an event

Arguments

event_list * l

an event list

event * e

an event

Description

ev_enqueue() stores the event e to the specified event list l which can be run by calling ev_run_list().


Function

void ev_schedule (event * e) -- schedule an event

Arguments

event * e

an event

Description

This function schedules an event by enqueueing it to a system-wide event list which is run by the platform dependent code whenever appropriate.


Function

int ev_run_list (event_list * l) -- run an event list

Arguments

event_list * l

an event list

Description

This function calls ev_run() for all events enqueued in the list l.

8.7 Sockets

Socket resources represent network connections. Their data structure (socket) contains a lot of fields defining the exact type of the socket, the local and remote addresses and ports, pointers to socket buffers and finally pointers to hook functions to be called when new data have arrived to the receive buffer (rx_hook), when the contents of the transmit buffer have been transmitted (tx_hook) and when an error or connection close occurs (err_hook).

Freeing of sockets from inside socket hooks is perfectly safe.


Function

int sk_setup_multicast (sock * s) -- enable multicast for given socket

Arguments

sock * s

socket

Description

Prepare transmission of multicast packets for given datagram socket. The socket must have defined iface.

Result

0 for success, -1 for an error.


Function

int sk_join_group (sock * s, ip_addr maddr) -- join multicast group for given socket

Arguments

sock * s

socket

ip_addr maddr

multicast address

Description

Join multicast group for given datagram socket and associated interface. The socket must have defined iface.

Result

0 for success, -1 for an error.


Function

int sk_leave_group (sock * s, ip_addr maddr) -- leave multicast group for given socket

Arguments

sock * s

socket

ip_addr maddr

multicast address

Description

Leave multicast group for given datagram socket and associated interface. The socket must have defined iface.

Result

0 for success, -1 for an error.


Function

int sk_setup_broadcast (sock * s) -- enable broadcast for given socket

Arguments

sock * s

socket

Description

Allow reception and transmission of broadcast packets for given datagram socket. The socket must have defined iface. For transmission, packets should be send to brd address of iface.

Result

0 for success, -1 for an error.


Function

int sk_set_ttl (sock * s, int ttl) -- set transmit TTL for given socket

Arguments

sock * s

socket

int ttl

TTL value

Description

Set TTL for already opened connections when TTL was not set before. Useful for accepted connections when different ones should have different TTL.

Result

0 for success, -1 for an error.


Function

int sk_set_min_ttl (sock * s, int ttl) -- set minimal accepted TTL for given socket

Arguments

sock * s

socket

int ttl

TTL value

Description

Set minimal accepted TTL for given socket. Can be used for TTL security. implementations.

Result

0 for success, -1 for an error.


Function

int sk_set_md5_auth (sock * s, ip_addr local, ip_addr remote, struct iface * ifa, char * passwd, int setkey) -- add / remove MD5 security association for given socket

Arguments

sock * s

socket

ip_addr local

IP address of local side

ip_addr remote

IP address of remote side

struct iface * ifa

Interface for link-local IP address

char * passwd

Password used for MD5 authentication

int setkey

Update also system SA/SP database

Description

In TCP MD5 handling code in kernel, there is a set of security associations used for choosing password and other authentication parameters according to the local and remote address. This function is useful for listening socket, for active sockets it may be enough to set s->password field.

When called with passwd != NULL, the new pair is added, When called with passwd == NULL, the existing pair is removed.

Note that while in Linux, the MD5 SAs are specific to socket, in BSD they are stored in global SA/SP database (but the behavior also must be enabled on per-socket basis). In case of multiple sockets to the same neighbor, the socket-specific state must be configured for each socket while global state just once per src-dst pair. The setkey argument controls whether the global state (SA/SP database) is also updated.

Result

0 for success, -1 for an error.


Function

int sk_set_ipv6_checksum (sock * s, int offset) -- specify IPv6 checksum offset for given socket

Arguments

sock * s

socket

int offset

offset

Description

Specify IPv6 checksum field offset for given raw IPv6 socket. After that, the kernel will automatically fill it for outgoing packets and check it for incoming packets. Should not be used on ICMPv6 sockets, where the position is known to the kernel.

Result

0 for success, -1 for an error.


Function

sock * sock_new (pool * p) -- create a socket

Arguments

pool * p

pool

Description

This function creates a new socket resource. If you want to use it, you need to fill in all the required fields of the structure and call sk_open() to do the actual opening of the socket.

The real function name is sock_new(), sk_new() is a macro wrapper to avoid collision with OpenSSL.


Function

int sk_open (sock * s) -- open a socket

Arguments

sock * s

socket

Description

This function takes a socket resource created by sk_new() and initialized by the user and binds a corresponding network connection to it.

Result

0 for success, -1 for an error.


Function

int sk_send (sock * s, unsigned len) -- send data to a socket

Arguments

sock * s

socket

unsigned len

number of bytes to send

Description

This function sends len bytes of data prepared in the transmit buffer of the socket s to the network connection. If the packet can be sent immediately, it does so and returns 1, else it queues the packet for later processing, returns 0 and calls the tx_hook of the socket when the tranmission takes place.


Function

int sk_send_to (sock * s, unsigned len, ip_addr addr, unsigned port) -- send data to a specific destination

Arguments

sock * s

socket

unsigned len

number of bytes to send

ip_addr addr

IP address to send the packet to

unsigned port

port to send the packet to

Description

This is a sk_send() replacement for connection-less packet sockets which allows destination of the packet to be chosen dynamically. Raw IP sockets should use 0 for port.


Function

void io_log_event (void * hook, void * data) -- mark approaching event into event log

Arguments

void * hook

event hook address

void * data

event data address

Description

Store info (hook, data, timestamp) about the following internal event into a circular event log (event_log). When latency tracking is enabled, the log entry is kept open (in event_open) so the duration can be filled later.


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