gvisor.dev/gvisor@v0.0.0-20240520182842-f9d4d51c7e0f/runsc/cmd/umount_unsafe.go (about)

     1  // Copyright 2022 The gVisor Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package cmd
    16  
    17  import (
    18  	"context"
    19  	"os"
    20  	"syscall"
    21  	"unsafe"
    22  
    23  	"github.com/google/subcommands"
    24  	"golang.org/x/sys/unix"
    25  	"gvisor.dev/gvisor/pkg/abi/linux"
    26  	"gvisor.dev/gvisor/runsc/cmd/util"
    27  	"gvisor.dev/gvisor/runsc/flag"
    28  )
    29  
    30  // Umount implements subcommands.Command for the "umount" command.
    31  type Umount struct {
    32  	syncFD int
    33  }
    34  
    35  // Name implements subcommands.Command.Name.
    36  func (*Umount) Name() string {
    37  	return "umount"
    38  }
    39  
    40  // Synopsis implements subcommands.Command.Synopsis.
    41  func (*Umount) Synopsis() string {
    42  	return "umount the specified directory lazily when one byte is read from sync-fd"
    43  }
    44  
    45  // Usage implements subcommands.Command.Usage.
    46  func (*Umount) Usage() string {
    47  	return `umount --sync-fd=FD <directory path>`
    48  }
    49  
    50  // SetFlags implements subcommands.Command.SetFlags.
    51  func (u *Umount) SetFlags(f *flag.FlagSet) {
    52  	f.IntVar(&u.syncFD, "sync-fd", -1, "")
    53  }
    54  
    55  // Execute implements subcommands.Command.Execute.
    56  func (u *Umount) Execute(_ context.Context, f *flag.FlagSet, args ...any) subcommands.ExitStatus {
    57  	if f.NArg() == 0 || f.NArg() > 1 {
    58  		f.Usage()
    59  		return subcommands.ExitUsageError
    60  	}
    61  
    62  	dirPath := f.Arg(0)
    63  
    64  	syncFile := os.NewFile(uintptr(u.syncFD), "sync file")
    65  	defer syncFile.Close()
    66  
    67  	buf := make([]byte, 1)
    68  	if l, err := syncFile.Read(buf); err != nil || l != 1 {
    69  		util.Fatalf("unable to read from the sync descriptor: %v, error %v", l, err)
    70  	}
    71  
    72  	if _, _, errno := unix.RawSyscall(
    73  		unix.SYS_UMOUNT2,
    74  		uintptr(unsafe.Pointer(syscall.StringBytePtr(dirPath))),
    75  		uintptr(linux.MNT_DETACH), 0); errno != 0 {
    76  		util.Fatalf("Unable to umount %s: errno %v", dirPath, errno)
    77  	}
    78  
    79  	return subcommands.ExitSuccess
    80  }