paths.go

Documentation: github.com/containerd/cgroups

     1  /*
     2     Copyright The containerd Authors.
     3  
     4     Licensed under the Apache License, Version 2.0 (the "License");
     5     you may not use this file except in compliance with the License.
     6     You may obtain a copy of the License at
     7  
     8         http://www.apache.org/licenses/LICENSE-2.0
     9  
    10     Unless required by applicable law or agreed to in writing, software
    11     distributed under the License is distributed on an "AS IS" BASIS,
    12     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    13     See the License for the specific language governing permissions and
    14     limitations under the License.
    15  */
    16  
    17  package cgroups
    18  
    19  import (
    20  	"errors"
    21  	"fmt"
    22  	"path/filepath"
    23  )
    24  
    25  type Path func(subsystem Name) (string, error)
    26  
    27  func RootPath(subsystem Name) (string, error) {
    28  	return "/", nil
    29  }
    30  
    31  // StaticPath returns a static path to use for all cgroups
    32  func StaticPath(path string) Path {
    33  	return func(_ Name) (string, error) {
    34  		return path, nil
    35  	}
    36  }
    37  
    38  // NestedPath will nest the cgroups based on the calling processes cgroup
    39  // placing its child processes inside its own path
    40  func NestedPath(suffix string) Path {
    41  	paths, err := ParseCgroupFile("/proc/self/cgroup")
    42  	if err != nil {
    43  		return errorPath(err)
    44  	}
    45  	return existingPath(paths, suffix)
    46  }
    47  
    48  // PidPath will return the correct cgroup paths for an existing process running inside a cgroup
    49  // This is commonly used for the Load function to restore an existing container
    50  func PidPath(pid int) Path {
    51  	p := fmt.Sprintf("/proc/%d/cgroup", pid)
    52  	paths, err := ParseCgroupFile(p)
    53  	if err != nil {
    54  		return errorPath(fmt.Errorf("parse cgroup file %s: %w", p, err))
    55  	}
    56  	return existingPath(paths, "")
    57  }
    58  
    59  // ErrControllerNotActive is returned when a controller is not supported or enabled
    60  var ErrControllerNotActive = errors.New("controller is not supported")
    61  
    62  func existingPath(paths map[string]string, suffix string) Path {
    63  	// localize the paths based on the root mount dest for nested cgroups
    64  	for n, p := range paths {
    65  		dest, err := getCgroupDestination(n)
    66  		if err != nil {
    67  			return errorPath(err)
    68  		}
    69  		rel, err := filepath.Rel(dest, p)
    70  		if err != nil {
    71  			return errorPath(err)
    72  		}
    73  		if rel == "." {
    74  			rel = dest
    75  		}
    76  		paths[n] = filepath.Join("/", rel)
    77  	}
    78  	return func(name Name) (string, error) {
    79  		root, ok := paths[string(name)]
    80  		if !ok {
    81  			if root, ok = paths["name="+string(name)]; !ok {
    82  				return "", ErrControllerNotActive
    83  			}
    84  		}
    85  		if suffix != "" {
    86  			return filepath.Join(root, suffix), nil
    87  		}
    88  		return root, nil
    89  	}
    90  }
    91  
    92  func subPath(path Path, subName string) Path {
    93  	return func(name Name) (string, error) {
    94  		p, err := path(name)
    95  		if err != nil {
    96  			return "", err
    97  		}
    98  		return filepath.Join(p, subName), nil
    99  	}
   100  }
   101  
   102  func errorPath(err error) Path {
   103  	return func(_ Name) (string, error) {
   104  		return "", err
   105  	}
   106  }
   107
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