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run: add support for swappable engines
This commit revamps `lib/run.go` to rely on an interface for the actual execution of the desired command, such that alternate ways to run a command in the container can be easily added. A flag has been added to the run command to select a non-default engine. The default (and currently only) engine is systemd-nspawn.
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Derek Gonyeo
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Mar 30, 2016
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,32 @@ | ||
| // Copyright 2015 The appc Authors | ||
| // | ||
| // Licensed under the Apache License, Version 2.0 (the "License"); | ||
| // you may not use this file except in compliance with the License. | ||
| // You may obtain a copy of the License at | ||
| // | ||
| // http://www.apache.org/licenses/LICENSE-2.0 | ||
| // | ||
| // Unless required by applicable law or agreed to in writing, software | ||
| // distributed under the License is distributed on an "AS IS" BASIS, | ||
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| // See the License for the specific language governing permissions and | ||
| // limitations under the License. | ||
|
|
||
| package engine | ||
|
|
||
| import ( | ||
| "github.com/appc/spec/schema/types" | ||
| ) | ||
|
|
||
| // Engine is an interface which is accepted by lib.Run, and used to perform the | ||
| // actual execution of a binary inside the container. | ||
| type Engine interface { | ||
| // Run executes a command inside a container. command is the path to the | ||
| // binary (post-chroot) to exec, args is the arguments to pass to the | ||
| // binary, environment is the set of environment variables to set for the | ||
| // binary, chroot is the path on the host where the container's root | ||
| // filesystem exists, and workingDir specifies the path inside the | ||
| // container that should be the current working directory for the binary. | ||
| // If workingDir is "", the default should be "/". | ||
| Run(command string, args []string, environment types.Environment, chroot, workingDir string) error | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,135 @@ | ||
| // Copyright 2015 The appc Authors | ||
| // | ||
| // Licensed under the Apache License, Version 2.0 (the "License"); | ||
| // you may not use this file except in compliance with the License. | ||
| // You may obtain a copy of the License at | ||
| // | ||
| // http://www.apache.org/licenses/LICENSE-2.0 | ||
| // | ||
| // Unless required by applicable law or agreed to in writing, software | ||
| // distributed under the License is distributed on an "AS IS" BASIS, | ||
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| // See the License for the specific language governing permissions and | ||
| // limitations under the License. | ||
|
|
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| package systemdnspawn | ||
|
|
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| import ( | ||
| "fmt" | ||
| "os" | ||
| "os/exec" | ||
| "path" | ||
| "strings" | ||
| "syscall" | ||
|
|
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| "github.com/appc/spec/schema/types" | ||
| ) | ||
|
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| var pathlist = []string{"/usr/local/sbin", "/usr/local/bin", "/usr/sbin", | ||
| "/usr/bin", "/sbin", "/bin"} | ||
|
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| type Engine struct{} | ||
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| func (e Engine) Run(command string, args []string, environment types.Environment, chroot, workingDir string) error { | ||
| nspawncmd := []string{"systemd-nspawn", "-D", chroot} | ||
|
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| systemdVersion, err := getSystemdVersion() | ||
| if err != nil { | ||
| return err | ||
| } | ||
|
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| if systemdVersion >= 209 { | ||
| nspawncmd = append(nspawncmd, "--quiet", "--register=no") | ||
| } | ||
| if workingDir != "" { | ||
| if systemdVersion < 229 { | ||
| return fmt.Errorf("the working dir can only be set on systems with systemd-nspawn >= 229") | ||
| } | ||
| nspawncmd = append(nspawncmd, "--chdir", workingDir) | ||
| } | ||
|
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| for _, envVar := range environment { | ||
| nspawncmd = append(nspawncmd, "--setenv", envVar.Name+"="+envVar.Value) | ||
| } | ||
|
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| nspawncmd = append(nspawncmd, "--setenv", "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin") | ||
|
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| abscmd, err := findCmdInPath(pathlist, command, chroot) | ||
| if err != nil { | ||
| return err | ||
| } | ||
|
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| finfo, err := os.Lstat(path.Join(chroot, abscmd)) | ||
| switch { | ||
| case os.IsNotExist(err): | ||
| return fmt.Errorf("binary %q doesn't exist", abscmd) | ||
| case err != nil: | ||
| return err | ||
| } | ||
|
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| if finfo.Mode()&os.ModeSymlink != 0 && systemdVersion < 228 { | ||
| fmt.Fprintf(os.Stderr, "Warning: %q is a symlink, which systemd-nspawn version %d might error on\n", abscmd, systemdVersion) | ||
| } | ||
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| nspawncmd = append(nspawncmd, abscmd) | ||
| nspawncmd = append(nspawncmd, args...) | ||
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| execCmd := exec.Command(nspawncmd[0], nspawncmd[1:]...) | ||
| execCmd.Stdout = os.Stdout | ||
| execCmd.Stderr = os.Stderr | ||
| execCmd.Env = []string{"SYSTEMD_LOG_LEVEL=err"} | ||
|
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| err = execCmd.Run() | ||
| if err == exec.ErrNotFound { | ||
| return fmt.Errorf("systemd-nspawn is required but not found") | ||
| } | ||
| if err == nil { | ||
| return nil | ||
| } | ||
| if exitErr, ok := err.(*exec.ExitError); ok { | ||
| code := exitErr.Sys().(syscall.WaitStatus).ExitStatus() | ||
| return fmt.Errorf("non-zero exit code: %d", code) | ||
| } | ||
| return err | ||
| } | ||
|
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| func getSystemdVersion() (int, error) { | ||
| _, err := exec.LookPath("systemctl") | ||
| if err == exec.ErrNotFound { | ||
| return 0, fmt.Errorf("system does not have systemd") | ||
| } | ||
|
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| blob, err := exec.Command("systemctl", "--version").Output() | ||
| if err != nil { | ||
| return 0, err | ||
| } | ||
| for _, line := range strings.Split(string(blob), "\n") { | ||
| if strings.HasPrefix(line, "systemd ") { | ||
| var version int | ||
| _, err := fmt.Sscanf(line, "systemd %d", &version) | ||
| if err != nil { | ||
| return 0, err | ||
| } | ||
| return version, nil | ||
| } | ||
| } | ||
| return 0, fmt.Errorf("error parsing output from `systemctl --version`") | ||
| } | ||
|
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| func findCmdInPath(pathlist []string, cmd, prefix string) (string, error) { | ||
| if path.IsAbs(cmd) { | ||
| return cmd, nil | ||
| } | ||
|
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| for _, p := range pathlist { | ||
| _, err := os.Lstat(path.Join(prefix, p, cmd)) | ||
| switch { | ||
| case os.IsNotExist(err): | ||
| continue | ||
| case err != nil: | ||
| return "", err | ||
| } | ||
| return path.Join(p, cmd), nil | ||
| } | ||
| return "", fmt.Errorf("%s not found in any of: %v", cmd, pathlist) | ||
| } |
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