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// Copyright 2020 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 host
import (
"math"
"syscall"
"golang.org/x/sys/unix"
"gvisor.dev/gvisor/pkg/abi/linux"
"gvisor.dev/gvisor/pkg/context"
"gvisor.dev/gvisor/pkg/fd"
"gvisor.dev/gvisor/pkg/safemem"
"gvisor.dev/gvisor/pkg/sentry/memmap"
"gvisor.dev/gvisor/pkg/sentry/vfs"
"gvisor.dev/gvisor/pkg/sync"
"gvisor.dev/gvisor/pkg/syserror"
"gvisor.dev/gvisor/pkg/usermem"
)
// defaultFileFD implements FileDescriptionImpl for non-socket, non-TTY files.
type defaultFileFD struct {
fileDescription
// canMap specifies whether we allow the file to be memory mapped.
canMap bool
// mu protects the fields below.
mu sync.Mutex
// offset specifies the current file offset.
offset int64
}
// TODO(gvisor.dev/issue/1672): Implement Waitable interface.
// PRead implements FileDescriptionImpl.
func (f *defaultFileFD) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts vfs.ReadOptions) (int64, error) {
// TODO(b/34716638): Some char devices do support offsets, e.g. /dev/null.
if f.inode.isStream {
return 0, syserror.ESPIPE
}
return readFromHostFD(ctx, f.inode.hostFD, dst, offset, int(opts.Flags))
}
// Read implements FileDescriptionImpl.
func (f *defaultFileFD) Read(ctx context.Context, dst usermem.IOSequence, opts vfs.ReadOptions) (int64, error) {
// TODO(b/34716638): Some char devices do support offsets, e.g. /dev/null.
if f.inode.isStream {
// These files can't be memory mapped, assert this.
if f.canMap {
panic("files that can return EWOULDBLOCK (sockets, pipes, etc.) cannot be memory mapped")
}
n, err := readFromHostFD(ctx, f.inode.hostFD, dst, -1, int(opts.Flags))
if isBlockError(err) {
// If we got any data at all, return it as a "completed" partial read
// rather than retrying until complete.
if n != 0 {
err = nil
} else {
err = syserror.ErrWouldBlock
}
}
return n, err
}
// TODO(gvisor.dev/issue/1672): Cache pages, when forced to do so.
f.mu.Lock()
n, err := readFromHostFD(ctx, f.inode.hostFD, dst, f.offset, int(opts.Flags))
f.offset += n
f.mu.Unlock()
return n, err
}
func readFromHostFD(ctx context.Context, hostFD int, dst usermem.IOSequence, offset int64, flags int) (int64, error) {
// TODO(gvisor.dev/issue/1672): Support select preadv2 flags.
if flags != 0 {
return 0, syserror.EOPNOTSUPP
}
var reader safemem.Reader
if offset == -1 {
reader = safemem.FromIOReader{fd.NewReadWriter(hostFD)}
} else {
reader = safemem.FromVecReaderFunc{
func(srcs [][]byte) (int64, error) {
n, err := unix.Preadv(hostFD, srcs, offset)
return int64(n), err
},
}
}
n, err := dst.CopyOutFrom(ctx, reader)
return int64(n), err
}
// PWrite implements FileDescriptionImpl.
func (f *defaultFileFD) PWrite(ctx context.Context, src usermem.IOSequence, offset int64, opts vfs.WriteOptions) (int64, error) {
// TODO(b/34716638): Some char devices do support offsets, e.g. /dev/null.
if f.inode.isStream {
return 0, syserror.ESPIPE
}
return writeToHostFD(ctx, f.inode.hostFD, src, offset, int(opts.Flags))
}
// Write implements FileDescriptionImpl.
func (f *defaultFileFD) Write(ctx context.Context, src usermem.IOSequence, opts vfs.WriteOptions) (int64, error) {
// TODO(b/34716638): Some char devices do support offsets, e.g. /dev/null.
if f.inode.isStream {
// These files can't be memory mapped, assert this.
if f.canMap {
panic("files that can return EWOULDBLOCK (sockets, pipes, etc.) cannot be memory mapped")
}
n, err := writeToHostFD(ctx, f.inode.hostFD, src, -1, int(opts.Flags))
if isBlockError(err) {
err = syserror.ErrWouldBlock
}
return n, err
}
// TODO(gvisor.dev/issue/1672): Cache pages, when forced to do so.
// TODO(gvisor.dev/issue/1672): Write to end of file and update offset if O_APPEND is set on this file.
f.mu.Lock()
n, err := writeToHostFD(ctx, f.inode.hostFD, src, f.offset, int(opts.Flags))
f.offset += n
f.mu.Unlock()
return n, err
}
func writeToHostFD(ctx context.Context, hostFD int, src usermem.IOSequence, offset int64, flags int) (int64, error) {
// TODO(gvisor.dev/issue/1672): Support select pwritev2 flags.
if flags != 0 {
return 0, syserror.EOPNOTSUPP
}
var writer safemem.Writer
if offset == -1 {
writer = safemem.FromIOWriter{fd.NewReadWriter(hostFD)}
} else {
writer = safemem.FromVecWriterFunc{
func(srcs [][]byte) (int64, error) {
n, err := unix.Pwritev(hostFD, srcs, offset)
return int64(n), err
},
}
}
n, err := src.CopyInTo(ctx, writer)
return int64(n), err
}
// Seek implements FileDescriptionImpl.
//
// Note that we do not support seeking on directories, since we do not even
// allow directory fds to be imported at all.
func (f *defaultFileFD) Seek(_ context.Context, offset int64, whence int32) (int64, error) {
// TODO(b/34716638): Some char devices do support seeking, e.g. /dev/null.
if f.inode.isStream {
return 0, syserror.ESPIPE
}
f.mu.Lock()
defer f.mu.Unlock()
switch whence {
case linux.SEEK_SET:
if offset < 0 {
return f.offset, syserror.EINVAL
}
f.offset = offset
case linux.SEEK_CUR:
// Check for overflow. Note that underflow cannot occur, since f.offset >= 0.
if offset > math.MaxInt64-f.offset {
return f.offset, syserror.EOVERFLOW
}
if f.offset+offset < 0 {
return f.offset, syserror.EINVAL
}
f.offset += offset
case linux.SEEK_END:
var s syscall.Stat_t
if err := syscall.Fstat(f.inode.hostFD, &s); err != nil {
return f.offset, err
}
size := s.Size
// Check for overflow. Note that underflow cannot occur, since size >= 0.
if offset > math.MaxInt64-size {
return f.offset, syserror.EOVERFLOW
}
if size+offset < 0 {
return f.offset, syserror.EINVAL
}
f.offset = size + offset
case linux.SEEK_DATA, linux.SEEK_HOLE:
// Modifying the offset in the host file table should not matter, since
// this is the only place where we use it.
//
// For reading and writing, we always rely on our internal offset.
n, err := unix.Seek(f.inode.hostFD, offset, int(whence))
if err != nil {
return f.offset, err
}
f.offset = n
default:
// Invalid whence.
return f.offset, syserror.EINVAL
}
return f.offset, nil
}
// Sync implements FileDescriptionImpl.
func (f *defaultFileFD) Sync(context.Context) error {
// TODO(gvisor.dev/issue/1672): Currently we do not support the SyncData optimization, so we always sync everything.
return unix.Fsync(f.inode.hostFD)
}
// ConfigureMMap implements FileDescriptionImpl.
func (f *defaultFileFD) ConfigureMMap(_ context.Context, opts *memmap.MMapOpts) error {
if !f.canMap {
return syserror.ENODEV
}
// TODO(gvisor.dev/issue/1672): Implement ConfigureMMap and Mappable interface.
return syserror.ENODEV
}
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