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:
- Resource pools (pool)
- Memory blocks
- Linear memory pools (linpool)
- Slabs (slab)
- Events (event)
- Timers (timer)
- Sockets (socket)
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, struct domain_generic * dom, const char * name) -- create a resource pool
Arguments
- pool * p
parent pool
- struct domain_generic * dom
-- undescribed --
- 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 (struct dump_request * dreq, void * res) -- dump a resource
Arguments
- struct dump_request * dreq
-- undescribed --
- 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) -- create a new linear memory pool
Arguments
- pool * p
pool
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 page size.
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
struct lp_state * lp_save (linpool * m) -- save the state of a linear memory pool
Arguments
- linpool * m
linear memory pool
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_delete (slab * s) -- destroy an existing Slab
Arguments
- slab * s
slab
Description
This function destroys the given Slab.
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_allocz (slab * s) -- allocate an object from Slab and zero it
Arguments
- slab * s
slab
Description
sl_allocz() allocates space for a single object from the Slab and returns a pointer to the object after zeroing out the object memory.
Function
void sl_free (void * oo) -- return a free object back to a Slab
Arguments
- 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_send (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
int ev_run_list_limited (event_list * l, uint limit) -- run an event list
Arguments
- event_list * l
an event list
- uint limit
-- undescribed --
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, struct birdloop * loop) -- open a socket
Arguments
- sock * s
socket
- struct birdloop * loop
loop
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, uint flag) -- mark approaching event into event log
Arguments
- void * hook
event hook address
- void * data
event data address
- uint flag
-- undescribed --
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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