lang: core: os: Add a modinfo function

Not sure if this will need renaming, but might be a useful family of
functions.

lang/core/os/modinfo.go

@@ -0,0 +1,212 @@
+// Mgmt
+// Copyright (C) James Shubin and the project contributors
+// Written by James Shubin <james@shubin.ca> and the project contributors
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+//
+// Additional permission under GNU GPL version 3 section 7
+//
+// If you modify this program, or any covered work, by linking or combining it
+// with embedded mcl code and modules (and that the embedded mcl code and
+// modules which link with this program, contain a copy of their source code in
+// the authoritative form) containing parts covered by the terms of any other
+// license, the licensors of this program grant you additional permission to
+// convey the resulting work. Furthermore, the licensors of this program grant
+// the original author, James Shubin, additional permission to update this
+// additional permission if he deems it necessary to achieve the goals of this
+// additional permission.
+
+package coreos
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/purpleidea/mgmt/lang/funcs"
+	"github.com/purpleidea/mgmt/lang/interfaces"
+	"github.com/purpleidea/mgmt/lang/types"
+	"github.com/purpleidea/mgmt/util/errwrap"
+	"github.com/purpleidea/mgmt/util/recwatch"
+
+	"github.com/purpleidea/lsmod"
+)
+
+const (
+	// ModinfoLoadedFuncName is the name this function is registered as.
+	ModinfoLoadedFuncName = "modinfo_loaded"
+
+	// arg names...
+	modinfoLoadedArgNameModule = "module"
+
+	// procModules is where the modules data comes from.
+	procModules = "/proc/modules"
+)
+
+func init() {
+	funcs.ModuleRegister(ModuleName, ModinfoLoadedFuncName, func() interfaces.Func { return &ModinfoLoadedFunc{} }) // must register the func and name
+}
+
+// ModinfoLoadedFunc is a function that determines if a linux module exists and
+// is loaded. This is similar to what you can determine from the `lsmod`
+// command. If the module does not even exist, this also returns false.
+type ModinfoLoadedFunc struct {
+	init *interfaces.Init
+	last types.Value // last value received to use for diff
+
+	modulename *string     // the active module name
+	result     types.Value // last calculated output
+}
+
+// String returns a simple name for this function. This is needed so this struct
+// can satisfy the pgraph.Vertex interface.
+func (obj *ModinfoLoadedFunc) String() string {
+	return ModinfoLoadedFuncName
+}
+
+// ArgGen returns the Nth arg name for this function.
+func (obj *ModinfoLoadedFunc) ArgGen(index int) (string, error) {
+	seq := []string{modinfoLoadedArgNameModule}
+	if l := len(seq); index >= l {
+		return "", fmt.Errorf("index %d exceeds arg length of %d", index, l)
+	}
+	return seq[index], nil
+}
+
+// Validate makes sure we've built our struct properly. It is usually unused for
+// normal functions that users can use directly.
+func (obj *ModinfoLoadedFunc) Validate() error {
+	return nil
+}
+
+// Info returns some static info about itself.
+func (obj *ModinfoLoadedFunc) Info() *interfaces.Info {
+	return &interfaces.Info{
+		Pure: false, // maybe false because the bool can change
+		Memo: false,
+		Fast: false,
+		Spec: false,
+		Sig:  types.NewType(fmt.Sprintf("func(%s str) bool", modinfoLoadedArgNameModule)),
+	}
+}
+
+// Init runs some startup code for this function.
+func (obj *ModinfoLoadedFunc) Init(init *interfaces.Init) error {
+	obj.init = init
+	return nil
+}
+
+// Stream returns the changing values that this func has over time.
+func (obj *ModinfoLoadedFunc) Stream(ctx context.Context) error {
+	defer close(obj.init.Output) // the sender closes
+
+	// create new watcher
+	// XXX: does this file produce inotify events?
+	recWatcher := &recwatch.RecWatcher{
+		Path:    procModules,
+		Recurse: false,
+		Opts: []recwatch.Option{
+			recwatch.Logf(obj.init.Logf),
+			recwatch.Debug(obj.init.Debug),
+		},
+	}
+	if err := recWatcher.Init(); err != nil {
+		return errwrap.Wrapf(err, "could not watch file")
+	}
+	defer recWatcher.Close()
+
+	for {
+		select {
+		case input, ok := <-obj.init.Input:
+			if !ok {
+				obj.init.Input = nil // don't infinite loop back
+				continue             // no more inputs, but don't return!
+			}
+			//if err := input.Type().Cmp(obj.Info().Sig.Input); err != nil {
+			//	return errwrap.Wrapf(err, "wrong function input")
+			//}
+
+			if obj.last != nil && input.Cmp(obj.last) == nil {
+				continue // value didn't change, skip it
+			}
+			obj.last = input // store for next
+
+			modulename := input.Struct()[modinfoLoadedArgNameModule].Str()
+			// TODO: add check for empty string
+			if obj.modulename != nil && *obj.modulename == modulename {
+				continue // nothing changed
+			}
+			obj.modulename = &modulename
+
+		case event, ok := <-recWatcher.Events():
+			if !ok {
+				return fmt.Errorf("no more events")
+			}
+			if err := event.Error; err != nil {
+				return errwrap.Wrapf(err, "error event received")
+			}
+
+			if obj.last == nil {
+				continue // still waiting for input values
+			}
+
+		case <-ctx.Done():
+			return nil
+		}
+
+		args, err := interfaces.StructToCallableArgs(obj.last) // []types.Value, error)
+		if err != nil {
+			return err
+		}
+
+		result, err := obj.Call(ctx, args)
+		if err != nil {
+			return err
+		}
+
+		// if the result is still the same, skip sending an update...
+		if obj.result != nil && result.Cmp(obj.result) == nil {
+			continue // result didn't change
+		}
+		obj.result = result // store new result
+
+		select {
+		case obj.init.Output <- obj.result: // send
+			// pass
+
+		case <-ctx.Done():
+			return nil
+		}
+	}
+}
+
+// Call this function with the input args and return the value if it is possible
+// to do so at this time.
+func (obj *ModinfoLoadedFunc) Call(ctx context.Context, args []types.Value) (types.Value, error) {
+	if len(args) < 1 {
+		return nil, fmt.Errorf("not enough args")
+	}
+	modulename := args[0].Str()
+
+	m, err := lsmod.LsMod()
+	if err != nil {
+		return nil, errwrap.Wrapf(err, "error reading modules")
+	}
+
+	// XXX: is there a difference between exists and loaded?
+	_, exists := m[modulename]
+
+	return &types.BoolValue{
+		V: exists,
+	}, nil
+}