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libct/cg/fs2: optimize setFreezer more

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Before this patch, setFreezer does

- open/read/close (to check if the freezer is supported)
- open/write/close (to set the value)
- open/read/close (to check the value)

Three opens is a bit excessive. Refactor to only open the file once:

- open (to check if the freezer is supported)
- write (to set the value)
- seek/read (to check the value)
- close

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
This commit is contained in:
Kir Kolyshkin
2021-05-14 11:38:36 -07:00
parent 5d193188db
commit 1069e4e9da
1 changed files with 22 additions and 13 deletions
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libcontainer/cgroups/fs2/freezer.go
+22 -13
View File
@@ -5,7 +5,6 @@ package fs2
import (
stdErrors "errors"
"os"
"strings"
"github.com/opencontainers/runc/libcontainer/cgroups/fscommon"
"github.com/opencontainers/runc/libcontainer/configs"
@@ -26,7 +25,8 @@ func setFreezer(dirPath string, state configs.FreezerState) error {
return errors.Errorf("invalid freezer state %q requested", state)
}
if err := supportsFreezer(dirPath); err != nil {
fd, err := fscommon.OpenFile(dirPath, "cgroup.freeze", unix.O_RDWR)
if err != nil {
// We can ignore this request as long as the user didn't ask us to
// freeze the container (since without the freezer cgroup, that's a
// no-op).
@@ -35,12 +35,13 @@ func setFreezer(dirPath string, state configs.FreezerState) error {
}
return errors.Wrap(err, "freezer not supported")
}
defer fd.Close()
if err := fscommon.WriteFile(dirPath, "cgroup.freeze", stateStr); err != nil {
if _, err := fd.WriteString(stateStr); err != nil {
return err
}
// Confirm that the cgroup did actually change states.
if actualState, err := getFreezer(dirPath); err != nil {
if actualState, err := readFreezer(fd); err != nil {
return err
} else if actualState != state {
return errors.Errorf(`expected "cgroup.freeze" to be in state %q but was in %q`, state, actualState)
@@ -48,13 +49,8 @@ func setFreezer(dirPath string, state configs.FreezerState) error {
return nil
}
func supportsFreezer(dirPath string) error {
_, err := fscommon.ReadFile(dirPath, "cgroup.freeze")
return err
}
func getFreezer(dirPath string) (configs.FreezerState, error) {
state, err := fscommon.ReadFile(dirPath, "cgroup.freeze")
fd, err := fscommon.OpenFile(dirPath, "cgroup.freeze", unix.O_RDONLY)
if err != nil {
// If the kernel is too old, then we just treat the freezer as being in
// an "undefined" state.
@@ -63,10 +59,23 @@ func getFreezer(dirPath string) (configs.FreezerState, error) {
}
return configs.Undefined, err
}
switch strings.TrimSpace(state) {
case "0":
defer fd.Close()
return readFreezer(fd)
}
func readFreezer(fd *os.File) (configs.FreezerState, error) {
if _, err := fd.Seek(0, 0); err != nil {
return configs.Undefined, err
}
state := make([]byte, 2)
if _, err := fd.Read(state); err != nil {
return configs.Undefined, err
}
switch string(state) {
case "0\n":
return configs.Thawed, nil
case "1":
case "1\n":
return configs.Frozen, nil
default:
return configs.Undefined, errors.Errorf(`unknown "cgroup.freeze" state: %q`, state)