[setup] socket() -------> creation of the capture socket
setsockopt() ---> allocation of the circular buffer (ring)
- mmap() ---------> maping of the allocated buffer to the
+ mmap() ---------> mapping of the allocated buffer to the
user process
[capture] poll() ---------> to wait for incoming packets
is done by a simple call to close(fd).
Next I will describe PACKET_MMAP settings and it's constraints,
-also the maping of the circular buffer in the user process and
+also the mapping of the circular buffer in the user process and
the use of this buffer.
--------------------------------------------------------------------------------
A frame can be of any size with the only condition it can fit in a block. A block
can only hold an integer number of frames, or in other words, a frame cannot
-be spawn accross two blocks so there are some datails you have to take into
-account when choosing the frame_size. See "Maping and use of the circular
+be spawned accross two blocks, so there are some details you have to take into
+account when choosing the frame_size. See "Mapping and use of the circular
buffer (ring)".
block #1
-kmalloc allocates any number of bytes of phisically contiguous memory from
-a pool of pre-determined sizes. This pool of memory is mantained by the slab
+kmalloc allocates any number of bytes of physically contiguous memory from
+a pool of pre-determined sizes. This pool of memory is maintained by the slab
allocator which is at the end the responsible for doing the allocation and
hence which imposes the maximum memory that kmalloc can allocate.
<block number> * <block size> / <frame size>
-Suposse the following parameters, which apply for 2.6 kernel and an
+Suppose the following parameters, which apply for 2.6 kernel and an
i386 architecture:
<size-max> = 131072 bytes
<pagesize> = 4096 bytes
<max-order> = 11
-and a value for <frame size> of 2048 byteas. These parameters will yield
+and a value for <frame size> of 2048 bytes. These parameters will yield
<block number> = 131072/4 = 32768 blocks
<block size> = 4096 << 11 = 8 MiB.
All memory allocations are not freed until the socket is closed. The memory
allocations are done with GFP_KERNEL priority, this basically means that
the allocation can wait and swap other process' memory in order to allocate
-the nececessary memory, so normally limits can be reached.
+the necessary memory, so normally limits can be reached.
Other constraints
-------------------
- struct tpacket_hdr
- pad to TPACKET_ALIGNMENT=16
- struct sockaddr_ll
- - Gap, chosen so that packet data (Start+tp_net) alignes to
+ - Gap, chosen so that packet data (Start+tp_net) aligns to
TPACKET_ALIGNMENT=16
- Start+tp_mac: [ Optional MAC header ]
- Start+tp_net: Packet data, aligned to TPACKET_ALIGNMENT=16.
tp_frame_size must be a multiple of TPACKET_ALIGNMENT
tp_frame_nr must be exactly frames_per_block*tp_block_nr
-Note that tp_block_size should be choosed to be a power of two or there will
+Note that tp_block_size should be chosen to be a power of two or there will
be a waste of memory.
--------------------------------------------------------------------------------
-+ Maping and use of the circular buffer (ring)
++ Mapping and use of the circular buffer (ring)
--------------------------------------------------------------------------------
-The maping of the buffer in the user process is done with the conventional
+The mapping of the buffer in the user process is done with the conventional
mmap function. Even the circular buffer is compound of several physically
discontiguous blocks of memory, they are contiguous to the user space, hence
just one call to mmap is needed:
git.openpandora.org / pandora-kernel.git / blobdiff