bpf: introduce BPF syscall and maps

[linux-2.6-microblaze.git] / Documentation / networking / filter.txt

diff --git a/Documentation/networking/filter.txt b/Documentation/networking/filter.txt
index c48a970..4a01d71 100644 (file)
--- a/Documentation/networking/filter.txt
+++ b/Documentation/networking/filter.txt
@@ -462,9 +462,9 @@ JIT compiler
 ------------
 
 The Linux kernel has a built-in BPF JIT compiler for x86_64, SPARC, PowerPC,
-ARM and s390 and can be enabled through CONFIG_BPF_JIT. The JIT compiler is
-transparently invoked for each attached filter from user space or for internal
-kernel users if it has been previously enabled by root:
+ARM, MIPS and s390 and can be enabled through CONFIG_BPF_JIT. The JIT compiler
+is transparently invoked for each attached filter from user space or for
+internal kernel users if it has been previously enabled by root:
 
   echo 1 > /proc/sys/net/core/bpf_jit_enable
 
@@ -951,7 +951,7 @@ Size modifier is one of ...
 
 Mode modifier is one of:
 
-  BPF_IMM  0x00  /* classic BPF only, reserved in eBPF */
+  BPF_IMM  0x00  /* used for 32-bit mov in classic BPF and 64-bit in eBPF */
   BPF_ABS  0x20
   BPF_IND  0x40
   BPF_MEM  0x60
@@ -995,6 +995,51 @@ BPF_XADD | BPF_DW | BPF_STX: lock xadd *(u64 *)(dst_reg + off16) += src_reg
 Where size is one of: BPF_B or BPF_H or BPF_W or BPF_DW. Note that 1 and
 2 byte atomic increments are not supported.
 
+eBPF has one 16-byte instruction: BPF_LD | BPF_DW | BPF_IMM which consists
+of two consecutive 'struct bpf_insn' 8-byte blocks and interpreted as single
+instruction that loads 64-bit immediate value into a dst_reg.
+Classic BPF has similar instruction: BPF_LD | BPF_W | BPF_IMM which loads
+32-bit immediate value into a register.
+
+eBPF maps
+---------
+'maps' is a generic storage of different types for sharing data between kernel
+and userspace.
+
+The maps are accessed from user space via BPF syscall, which has commands:
+- create a map with given type and attributes
+  map_fd = bpf(BPF_MAP_CREATE, union bpf_attr *attr, u32 size)
+  using attr->map_type, attr->key_size, attr->value_size, attr->max_entries
+  returns process-local file descriptor or negative error
+
+- lookup key in a given map
+  err = bpf(BPF_MAP_LOOKUP_ELEM, union bpf_attr *attr, u32 size)
+  using attr->map_fd, attr->key, attr->value
+  returns zero and stores found elem into value or negative error
+
+- create or update key/value pair in a given map
+  err = bpf(BPF_MAP_UPDATE_ELEM, union bpf_attr *attr, u32 size)
+  using attr->map_fd, attr->key, attr->value
+  returns zero or negative error
+
+- find and delete element by key in a given map
+  err = bpf(BPF_MAP_DELETE_ELEM, union bpf_attr *attr, u32 size)
+  using attr->map_fd, attr->key
+
+- to delete map: close(fd)
+  Exiting process will delete maps automatically
+
+userspace programs use this syscall to create/access maps that eBPF programs
+are concurrently updating.
+
+maps can have different types: hash, array, bloom filter, radix-tree, etc.
+
+The map is defined by:
+  . type
+  . max number of elements
+  . key size in bytes
+  . value size in bytes
+
 Testing
 -------