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shm.lua
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shm.lua
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-- Use of this source code is governed by the Apache 2.0 license; see COPYING.
-- shm.lua -- shared memory alternative to ffi.new()
module(..., package.seeall)
local ffi = require("ffi")
local lib = require("core.lib")
local S = require("syscall")
local const = require("syscall.linux.constants")
-- Root directory where the object tree is created.
root = os.getenv("SNABB_SHM_ROOT") or "/var/run/snabb"
-- Table (address->size) of all currently mapped objects.
mappings = {}
-- Map an object into memory.
local function map (name, type, readonly, create, ...)
local path = resolve(name)
local mapmode = readonly and 'read' or 'read, write'
local ctype = ffi.typeof(type)
local size = ffi.sizeof(ctype, ...)
local stat = S.stat(root..'/'..path)
if stat and stat.size < size then
print(("shm warning: resizing %s from %d to %d bytes")
:format(path, stat.size, size))
end
local fd, err
if create then
-- Create the parent directories. If this fails then so will the open().
mkdir(lib.dirname(path))
fd, err = S.open(root..'/'..path, "creat, rdwr", "rusr, wusr, rgrp, roth")
else
fd, err = S.open(root..'/'..path, readonly and "rdonly" or "rdwr")
end
if not fd then error("shm open error ("..path.."):"..tostring(err)) end
if create then
assert(fd:ftruncate(size), "shm: ftruncate failed")
else
assert(fd:fstat().size >= size, "shm: unexpected size")
end
local mem, err = S.mmap(nil, size, mapmode, "shared", fd, 0)
fd:close()
if mem == nil then error("mmap failed: " .. tostring(err)) end
mappings[pointer_to_number(mem)] = size
return ffi.cast(ffi.typeof("$&", ctype), mem)
end
function create (name, type, ...)
return map(name, type, false, true, ...)
end
function open (name, type, readonly, ...)
return map(name, type, readonly, false, ...)
end
function exists (name)
local path = resolve(name)
local fd = S.open(root..'/'..path, "rdonly")
return fd and fd:close()
end
function alias (name, target)
mkdir(lib.dirname(resolve(name)))
assert(S.symlink(root.."/"..resolve(target), root.."/"..resolve(name)))
end
function resolve (name)
local q, p = name:match("^(/*)(.*)") -- split qualifier (/)
local result = p
if q ~= '/' then result = tostring(S.getpid()).."/"..result end
return result
end
function path (name)
return root..'/'..resolve(name)
end
-- Make the named subdirectory in the shm folder.
function mkdir (name)
-- Create root with mode "rwxr-xr-x" if it does not exist yet.
if not S.stat(root) then
local mask = S.umask(0)
local status, err = S.mkdir(root, "00755")
assert(status or err.errno == const.E.EXIST, ("Unable to create %s: %s"):format(
root, tostring(err or "unspecified error")))
S.umask(mask)
end
-- Create sub directories
local dir = root
name:gsub("([^/]+)",
function (x)
dir = dir.."/"..x
S.mkdir(dir, "rwxu, rgrp, xgrp, roth, xoth")
end)
end
-- Delete a shared object memory mapping.
-- The pointer must have been returned by map().
function unmap (ptr)
local size = mappings[pointer_to_number(ptr)]
assert(size, "shm mapping not found")
S.munmap(ptr, size)
mappings[pointer_to_number(ptr)] = nil
end
function pointer_to_number (ptr)
return tonumber(ffi.cast("uint64_t", ffi.cast("void*", ptr)))
end
-- Unlink names from their objects.
function unlink (name)
local path = resolve(name)
-- Note: Recursive delete is dangerous, important it is under $root!
return S.util.rm(root..'/'..path) -- recursive rm of file or directory
end
-- Return an array of objects under the prefix name.
-- The names are returned unqualified e.g. 'x' and not 'foo/bar/x'.
function children (name)
-- XXX dirtable returns an array but with a special tostring metamethod.
-- Potentially confusing? (Copy into plain array instead?)
return S.util.dirtable(root.."/"..resolve(name), true) or {}
end
-- Type registry for modules that implement abstract shm objects.
types = {}
function register (type, module)
assert(module, "Must supply module")
assert(not types[type], "Duplicate shm type: "..type)
types[type] = module
return type
end
-- Create a directory of shm objects defined by specs under path.
function create_frame (path, specs)
local frame = {}
frame.specs = specs
frame.path = path.."/"
for name, spec in pairs(specs) do
assert(frame[name] == nil, "shm: duplicate name: "..name)
local module = spec[1]
local initargs = lib.array_copy(spec)
table.remove(initargs, 1) -- strip type name from spec
frame[name] = module.create(frame.path..name.."."..module.type,
unpack(initargs))
end
return frame
end
-- Open a directory of shm objects for reading, determine their types by file
-- extension.
function open_frame (path)
local frame = {}
frame.specs = {}
frame.path = path.."/"
frame.readonly = true
for _, file in ipairs(children(path)) do
local name, type = file:match("(.*)[.](.*)$")
local module = types[type]
if module then
assert(frame[name] == nil, "shm: duplicate name: "..name)
frame[name] = module.open(frame.path..file, 'readonly')
frame.specs[name] = {module}
end
end
return frame
end
-- Delete/unmap a frame of shm objects. The frame's directory is unlinked if
-- the frame was created by create_frame.
function delete_frame (frame)
for name, spec in pairs(frame.specs) do
local module = spec[1]
if rawget(module, 'delete') then
module.delete(frame.path..name.."."..module.type)
else
unmap(frame[name])
end
end
if not frame.readonly then
unlink(frame.path)
end
end
function selftest ()
print("selftest: shm")
print("checking resolve..")
pid = tostring(S.getpid())
local p1 = resolve("/"..pid.."/foo/bar/baz/beer")
local p2 = resolve("foo/bar/baz/beer")
assert(p1 == p2, p1.." ~= "..p2)
print("checking shared memory..")
local name = "shm/selftest/obj"
print("create "..name)
local p1 = create(name, "struct { int x, y, z; }")
local p2 = create(name, "struct { int x, y, z; }")
assert(p1 ~= p2)
assert(p1.x == p2.x)
p1.x = 42
assert(p1.x == p2.x)
assert(unlink(name))
unmap(p1)
unmap(p2)
print("checking exists..")
assert(not exists(name))
local p1 = create(name, "struct { int x, y, z; }")
assert(exists(name))
assert(unlink(name))
unmap(p1)
assert(not exists(name))
-- Checking parameterized types
print("checking parameterized types..")
local name = "shm/selftest/parameterized"
local p1 = create(name, "struct { int x; int xs[?]; }", 10)
local p2 = open(name, "struct { int x; int xs[?]; }", 'read-only', 10)
p1.xs[9] = 42
assert(p2.xs[9] == 42)
unmap(p2)
unmap(p1)
assert(unlink(name))
-- Test that we can open and cleanup many objects
print("checking many objects..")
local path = 'shm/selftest/manyobj'
local n = 10000
local objs = {}
for i = 1, n do
table.insert(objs, create(path.."/"..i, "uint64_t[1]"))
end
print(n.." objects created")
for i = 1, n do unmap(objs[i]) end
print(n.." objects unmapped")
assert((#children(path)) == n, "child count mismatch")
assert(unlink("shm"))
print("selftest ok")
end