7493debe26
This allows consumers to read back the pidFile and to check if the PID is still running. Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
52 lines
1.6 KiB
Go
52 lines
1.6 KiB
Go
// Package pidfile provides structure and helper functions to create and remove
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// PID file. A PID file is usually a file used to store the process ID of a
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// running process.
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package pidfile // import "github.com/docker/docker/pkg/pidfile"
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import (
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"bytes"
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"fmt"
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"os"
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"strconv"
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"github.com/docker/docker/pkg/process"
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)
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// Read reads the "PID file" at path, and returns the PID if it contains a
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// valid PID of a running process, or 0 otherwise. It returns an error when
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// failing to read the file, or if the file doesn't exist, but malformed content
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// is ignored. Consumers should therefore check if the returned PID is a non-zero
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// value before use.
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func Read(path string) (pid int, err error) {
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pidByte, err := os.ReadFile(path)
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if err != nil {
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return 0, err
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}
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pid, err = strconv.Atoi(string(bytes.TrimSpace(pidByte)))
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if err != nil {
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return 0, nil
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}
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if pid != 0 && process.Alive(pid) {
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return pid, nil
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}
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return 0, nil
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}
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// Write writes a "PID file" at the specified path. It returns an error if the
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// file exists and contains a valid PID of a running process, or when failing
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// to write the file.
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func Write(path string, pid int) error {
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if pid < 1 {
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// We might be running as PID 1 when running docker-in-docker,
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// but 0 or negative PIDs are not acceptable.
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return fmt.Errorf("invalid PID (%d): only positive PIDs are allowed", pid)
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}
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oldPID, err := Read(path)
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if err != nil && !os.IsNotExist(err) {
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return err
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}
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if oldPID != 0 {
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return fmt.Errorf("process with PID %d is still running", oldPID)
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}
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return os.WriteFile(path, []byte(strconv.Itoa(pid)), 0o644)
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}
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