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libct/specconv: reduce init allocations, use global maps, refactor #3281

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Merged
thaJeztah merged 6 commits into from
Nov 17, 2021
Merged

libct/specconv: reduce init allocations, use global maps, refactor #3281

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8fe1e8b
libct/specconv: rm some init allocations
kolyshkin Sep 23, 2021
81586e1
libct/specconv: reuse mountPropagationMapping in parseMountOptions
kolyshkin Nov 12, 2021
2c3792b
libct/specconv: make mountFlags and extensionFlags global
kolyshkin Nov 12, 2021
37c5fd5
libct/specconv: make parseMountOptions return Mount
kolyshkin Nov 12, 2021
6907bec
libct/specconv: remove isSecSuffix regex
kolyshkin Nov 13, 2021
029b73c
libct/spec: replace isValidName regex with a function
kolyshkin Nov 13, 2021
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51 changes: 32 additions & 19 deletions libcontainer/specconv/spec_linux.go
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,7 @@ import (
"path/filepath"
"regexp"
"strings"
"sync"
"time"

systemdDbus "github.com/coreos/go-systemd/v22/dbus"
Expand All @@ -24,26 +25,36 @@ import (
"golang.org/x/sys/unix"
)

var namespaceMapping = map[specs.LinuxNamespaceType]configs.NamespaceType{
specs.PIDNamespace: configs.NEWPID,
specs.NetworkNamespace: configs.NEWNET,
specs.MountNamespace: configs.NEWNS,
specs.UserNamespace: configs.NEWUSER,
specs.IPCNamespace: configs.NEWIPC,
specs.UTSNamespace: configs.NEWUTS,
specs.CgroupNamespace: configs.NEWCGROUP,
}
var (
initMapsOnce sync.Once
namespaceMapping map[specs.LinuxNamespaceType]configs.NamespaceType
mountPropagationMapping map[string]int
)

var mountPropagationMapping = map[string]int{
"rprivate": unix.MS_PRIVATE | unix.MS_REC,
"private": unix.MS_PRIVATE,
"rslave": unix.MS_SLAVE | unix.MS_REC,
"slave": unix.MS_SLAVE,
"rshared": unix.MS_SHARED | unix.MS_REC,
"shared": unix.MS_SHARED,
"runbindable": unix.MS_UNBINDABLE | unix.MS_REC,
"unbindable": unix.MS_UNBINDABLE,
"": 0,
func initMaps() {
initMapsOnce.Do(func() {
namespaceMapping = map[specs.LinuxNamespaceType]configs.NamespaceType{
specs.PIDNamespace: configs.NEWPID,
specs.NetworkNamespace: configs.NEWNET,
specs.MountNamespace: configs.NEWNS,
specs.UserNamespace: configs.NEWUSER,
specs.IPCNamespace: configs.NEWIPC,
specs.UTSNamespace: configs.NEWUTS,
specs.CgroupNamespace: configs.NEWCGROUP,
}

mountPropagationMapping = map[string]int{
"rprivate": unix.MS_PRIVATE | unix.MS_REC,
"private": unix.MS_PRIVATE,
"rslave": unix.MS_SLAVE | unix.MS_REC,
"slave": unix.MS_SLAVE,
"rshared": unix.MS_SHARED | unix.MS_REC,
"shared": unix.MS_SHARED,
"runbindable": unix.MS_UNBINDABLE | unix.MS_REC,
"unbindable": unix.MS_UNBINDABLE,
"": 0,
}
})
}

// AllowedDevices is the set of devices which are automatically included for
Expand Down Expand Up @@ -256,6 +267,8 @@ func CreateLibcontainerConfig(opts *CreateOpts) (*configs.Config, error) {
config.Cgroups = c
// set linux-specific config
if spec.Linux != nil {
initMaps()
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@thaJeztah thaJeztah Nov 17, 2021

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I like the improvement that's brought by this, but (as a follow-up) perhaps we should consider having utilities / accessor functions for these variables, so that the initialisation happens more 'organically' (reducing the cognitive overload of having to thing about first calling initMap() whenever we need to use one of the variables.

In this case it could be a function to check if foo exists in mountPropagationMapping

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@kolyshkin kolyshkin Nov 18, 2021

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Do you mean something like

func getNamespaceMapping() map[specs.LinuxNamespaceType]configs.NamespaceType {
    initMaps()
    return namespaceMapping
}

// ... and so on for every other map we lazy init.
....

nsMap := getNamespaceMapping()

To me it looks like a bloat, since the nsMap := getNamespaceMapping() is just a way to sugar-coat initMaps().

A runtime assertion would be nice. If only accessing a nil map would panic....

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@kolyshkin kolyshkin Nov 18, 2021

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I can't think of anything better than

if namespaceMapping == nil {
   panic("uninitialied map") // we have a bug in the code
}

but it's still inferior to

initMaps()

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@kolyshkin kolyshkin Nov 18, 2021

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Some kind of a linter to which we can add a rule (in the source code) like "X should be called before using Y" would also be nice to have.

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@kolyshkin kolyshkin Nov 18, 2021

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Ideally, a lazy way to initialize variables. IOW same as this PR does, but automatically (perhaps via an annotation).

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@kolyshkin kolyshkin Nov 18, 2021 •
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Someone worked on something like this -- alas it does not look good without generics. https://github.com/zetamatta/go-lazy

I guess we have to postpone it till Go 2.0 ))))


var exists bool
if config.RootPropagation, exists = mountPropagationMapping[spec.Linux.RootfsPropagation]; !exists {
return nil, fmt.Errorf("rootfsPropagation=%v is not supported", spec.Linux.RootfsPropagation)
Expand Down