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// Copyright 2019 The gVisor 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 vfs
import (
"gvisor.dev/gvisor/pkg/abi/linux"
"gvisor.dev/gvisor/pkg/sentry/context"
"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
"gvisor.dev/gvisor/pkg/syserror"
)
// PathOperation specifies the path operated on by a VFS method.
//
// PathOperation is passed to VFS methods by pointer to reduce memory copying:
// it's somewhat large and should never escape. (Options structs are passed by
// pointer to VFS and FileDescription methods for the same reason.)
type PathOperation struct {
// Root is the VFS root. References on Root are borrowed from the provider
// of the PathOperation.
//
// Invariants: Root.Ok().
Root VirtualDentry
// Start is the starting point for the path traversal. References on Start
// are borrowed from the provider of the PathOperation (i.e. the caller of
// the VFS method to which the PathOperation was passed).
//
// Invariants: Start.Ok(). If Pathname.Absolute, then Start == Root.
Start VirtualDentry
// Path is the pathname traversed by this operation.
Pathname string
// If FollowFinalSymlink is true, and the Dentry traversed by the final
// path component represents a symbolic link, the symbolic link should be
// followed.
FollowFinalSymlink bool
}
// GetDentryAt returns a VirtualDentry representing the given path, at which a
// file must exist. A reference is taken on the returned VirtualDentry.
func (vfs *VirtualFilesystem) GetDentryAt(ctx context.Context, creds *auth.Credentials, pop *PathOperation, opts *GetDentryOptions) (VirtualDentry, error) {
rp, err := vfs.getResolvingPath(creds, pop)
if err != nil {
return VirtualDentry{}, err
}
for {
d, err := rp.mount.fs.impl.GetDentryAt(ctx, rp, *opts)
if err == nil {
vd := VirtualDentry{
mount: rp.mount,
dentry: d,
}
rp.mount.incRef()
vfs.putResolvingPath(rp)
return vd, nil
}
if !rp.handleError(err) {
vfs.putResolvingPath(rp)
return VirtualDentry{}, err
}
}
}
// MkdirAt creates a directory at the given path.
func (vfs *VirtualFilesystem) MkdirAt(ctx context.Context, creds *auth.Credentials, pop *PathOperation, opts *MkdirOptions) error {
// "Under Linux, apart from the permission bits, the S_ISVTX mode bit is
// also honored." - mkdir(2)
opts.Mode &= 01777
rp, err := vfs.getResolvingPath(creds, pop)
if err != nil {
return err
}
for {
err := rp.mount.fs.impl.MkdirAt(ctx, rp, *opts)
if err == nil {
vfs.putResolvingPath(rp)
return nil
}
if !rp.handleError(err) {
vfs.putResolvingPath(rp)
return err
}
}
}
// MknodAt creates a file of the given mode at the given path. It returns an
// error from the syserror package.
func (vfs *VirtualFilesystem) MknodAt(ctx context.Context, creds *auth.Credentials, pop *PathOperation, opts *MknodOptions) error {
rp, err := vfs.getResolvingPath(creds, pop)
if err != nil {
return nil
}
for {
if err = rp.mount.fs.impl.MknodAt(ctx, rp, *opts); err == nil {
vfs.putResolvingPath(rp)
return nil
}
// Handle mount traversals.
if !rp.handleError(err) {
vfs.putResolvingPath(rp)
return err
}
}
}
// OpenAt returns a FileDescription providing access to the file at the given
// path. A reference is taken on the returned FileDescription.
func (vfs *VirtualFilesystem) OpenAt(ctx context.Context, creds *auth.Credentials, pop *PathOperation, opts *OpenOptions) (*FileDescription, error) {
// Remove:
//
// - O_LARGEFILE, which we always report in FileDescription status flags
// since only 64-bit architectures are supported at this time.
//
// - O_CLOEXEC, which affects file descriptors and therefore must be
// handled outside of VFS.
//
// - Unknown flags.
opts.Flags &= linux.O_ACCMODE | linux.O_CREAT | linux.O_EXCL | linux.O_NOCTTY | linux.O_TRUNC | linux.O_APPEND | linux.O_NONBLOCK | linux.O_DSYNC | linux.O_ASYNC | linux.O_DIRECT | linux.O_DIRECTORY | linux.O_NOFOLLOW | linux.O_NOATIME | linux.O_SYNC | linux.O_PATH | linux.O_TMPFILE
// Linux's __O_SYNC (which we call linux.O_SYNC) implies O_DSYNC.
if opts.Flags&linux.O_SYNC != 0 {
opts.Flags |= linux.O_DSYNC
}
// Linux's __O_TMPFILE (which we call linux.O_TMPFILE) must be specified
// with O_DIRECTORY and a writable access mode (to ensure that it fails on
// filesystem implementations that do not support it).
if opts.Flags&linux.O_TMPFILE != 0 {
if opts.Flags&linux.O_DIRECTORY == 0 {
return nil, syserror.EINVAL
}
if opts.Flags&linux.O_CREAT != 0 {
return nil, syserror.EINVAL
}
if opts.Flags&linux.O_ACCMODE == linux.O_RDONLY {
return nil, syserror.EINVAL
}
}
// O_PATH causes most other flags to be ignored.
if opts.Flags&linux.O_PATH != 0 {
opts.Flags &= linux.O_DIRECTORY | linux.O_NOFOLLOW | linux.O_PATH
}
// "On Linux, the following bits are also honored in mode: [S_ISUID,
// S_ISGID, S_ISVTX]" - open(2)
opts.Mode &= 07777
if opts.Flags&linux.O_NOFOLLOW != 0 {
pop.FollowFinalSymlink = false
}
rp, err := vfs.getResolvingPath(creds, pop)
if err != nil {
return nil, err
}
if opts.Flags&linux.O_DIRECTORY != 0 {
rp.mustBeDir = true
rp.mustBeDirOrig = true
}
for {
fd, err := rp.mount.fs.impl.OpenAt(ctx, rp, *opts)
if err == nil {
vfs.putResolvingPath(rp)
return fd, nil
}
if !rp.handleError(err) {
vfs.putResolvingPath(rp)
return nil, err
}
}
}
// StatAt returns metadata for the file at the given path.
func (vfs *VirtualFilesystem) StatAt(ctx context.Context, creds *auth.Credentials, pop *PathOperation, opts *StatOptions) (linux.Statx, error) {
rp, err := vfs.getResolvingPath(creds, pop)
if err != nil {
return linux.Statx{}, err
}
for {
stat, err := rp.mount.fs.impl.StatAt(ctx, rp, *opts)
if err == nil {
vfs.putResolvingPath(rp)
return stat, nil
}
if !rp.handleError(err) {
vfs.putResolvingPath(rp)
return linux.Statx{}, err
}
}
}
// StatusFlags returns file description status flags.
func (fd *FileDescription) StatusFlags(ctx context.Context) (uint32, error) {
flags, err := fd.impl.StatusFlags(ctx)
flags |= linux.O_LARGEFILE
return flags, err
}
// SetStatusFlags sets file description status flags.
func (fd *FileDescription) SetStatusFlags(ctx context.Context, flags uint32) error {
return fd.impl.SetStatusFlags(ctx, flags)
}
// TODO:
//
// - VFS.SyncAllFilesystems() for sync(2)
//
// - Something for syncfs(2)
//
// - VFS.LinkAt()
//
// - VFS.ReadlinkAt()
//
// - VFS.RenameAt()
//
// - VFS.RmdirAt()
//
// - VFS.SetStatAt()
//
// - VFS.StatFSAt()
//
// - VFS.SymlinkAt()
//
// - VFS.UnlinkAt()
//
// - FileDescription.(almost everything)
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