255 lines
9.3 KiB
Go
255 lines
9.3 KiB
Go
// Copyright 2019 The gVisor Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package vfs
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import (
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"bytes"
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"io"
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"sync"
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"gvisor.dev/gvisor/pkg/abi/linux"
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"gvisor.dev/gvisor/pkg/sentry/arch"
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"gvisor.dev/gvisor/pkg/sentry/context"
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"gvisor.dev/gvisor/pkg/sentry/memmap"
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"gvisor.dev/gvisor/pkg/sentry/usermem"
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"gvisor.dev/gvisor/pkg/syserror"
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"gvisor.dev/gvisor/pkg/waiter"
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)
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// The following design pattern is strongly recommended for filesystem
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// implementations to adapt:
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// - Have a local fileDescription struct (containing FileDescription) which
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// embeds FileDescriptionDefaultImpl and overrides the default methods
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// which are common to all fd implementations for that for that filesystem
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// like StatusFlags, SetStatusFlags, Stat, SetStat, StatFS, etc.
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// - This should be embedded in all file description implementations as the
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// first field by value.
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// - Directory FDs would also embed DirectoryFileDescriptionDefaultImpl.
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// FileDescriptionDefaultImpl may be embedded by implementations of
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// FileDescriptionImpl to obtain implementations of many FileDescriptionImpl
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// methods with default behavior analogous to Linux's.
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type FileDescriptionDefaultImpl struct{}
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// OnClose implements FileDescriptionImpl.OnClose analogously to
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// file_operations::flush == NULL in Linux.
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func (FileDescriptionDefaultImpl) OnClose() error {
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return nil
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}
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// StatFS implements FileDescriptionImpl.StatFS analogously to
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// super_operations::statfs == NULL in Linux.
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func (FileDescriptionDefaultImpl) StatFS(ctx context.Context) (linux.Statfs, error) {
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return linux.Statfs{}, syserror.ENOSYS
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}
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// Readiness implements waiter.Waitable.Readiness analogously to
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// file_operations::poll == NULL in Linux.
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func (FileDescriptionDefaultImpl) Readiness(mask waiter.EventMask) waiter.EventMask {
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// include/linux/poll.h:vfs_poll() => DEFAULT_POLLMASK
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return waiter.EventIn | waiter.EventOut
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}
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// EventRegister implements waiter.Waitable.EventRegister analogously to
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// file_operations::poll == NULL in Linux.
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func (FileDescriptionDefaultImpl) EventRegister(e *waiter.Entry, mask waiter.EventMask) {
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}
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// EventUnregister implements waiter.Waitable.EventUnregister analogously to
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// file_operations::poll == NULL in Linux.
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func (FileDescriptionDefaultImpl) EventUnregister(e *waiter.Entry) {
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}
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// PRead implements FileDescriptionImpl.PRead analogously to
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// file_operations::read == file_operations::read_iter == NULL in Linux.
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func (FileDescriptionDefaultImpl) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts ReadOptions) (int64, error) {
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return 0, syserror.EINVAL
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}
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// Read implements FileDescriptionImpl.Read analogously to
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// file_operations::read == file_operations::read_iter == NULL in Linux.
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func (FileDescriptionDefaultImpl) Read(ctx context.Context, dst usermem.IOSequence, opts ReadOptions) (int64, error) {
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return 0, syserror.EINVAL
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}
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// PWrite implements FileDescriptionImpl.PWrite analogously to
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// file_operations::write == file_operations::write_iter == NULL in Linux.
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func (FileDescriptionDefaultImpl) PWrite(ctx context.Context, src usermem.IOSequence, offset int64, opts WriteOptions) (int64, error) {
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return 0, syserror.EINVAL
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}
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// Write implements FileDescriptionImpl.Write analogously to
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// file_operations::write == file_operations::write_iter == NULL in Linux.
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func (FileDescriptionDefaultImpl) Write(ctx context.Context, src usermem.IOSequence, opts WriteOptions) (int64, error) {
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return 0, syserror.EINVAL
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}
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// IterDirents implements FileDescriptionImpl.IterDirents analogously to
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// file_operations::iterate == file_operations::iterate_shared == NULL in
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// Linux.
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func (FileDescriptionDefaultImpl) IterDirents(ctx context.Context, cb IterDirentsCallback) error {
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return syserror.ENOTDIR
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}
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// Seek implements FileDescriptionImpl.Seek analogously to
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// file_operations::llseek == NULL in Linux.
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func (FileDescriptionDefaultImpl) Seek(ctx context.Context, offset int64, whence int32) (int64, error) {
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return 0, syserror.ESPIPE
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}
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// Sync implements FileDescriptionImpl.Sync analogously to
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// file_operations::fsync == NULL in Linux.
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func (FileDescriptionDefaultImpl) Sync(ctx context.Context) error {
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return syserror.EINVAL
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}
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// ConfigureMMap implements FileDescriptionImpl.ConfigureMMap analogously to
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// file_operations::mmap == NULL in Linux.
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func (FileDescriptionDefaultImpl) ConfigureMMap(ctx context.Context, opts memmap.MMapOpts) error {
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return syserror.ENODEV
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}
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// Ioctl implements FileDescriptionImpl.Ioctl analogously to
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// file_operations::unlocked_ioctl == NULL in Linux.
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func (FileDescriptionDefaultImpl) Ioctl(ctx context.Context, uio usermem.IO, args arch.SyscallArguments) (uintptr, error) {
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return 0, syserror.ENOTTY
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}
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// DirectoryFileDescriptionDefaultImpl may be embedded by implementations of
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// FileDescriptionImpl that always represent directories to obtain
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// implementations of non-directory I/O methods that return EISDIR.
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type DirectoryFileDescriptionDefaultImpl struct{}
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// PRead implements FileDescriptionImpl.PRead.
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func (DirectoryFileDescriptionDefaultImpl) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts ReadOptions) (int64, error) {
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return 0, syserror.EISDIR
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}
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// Read implements FileDescriptionImpl.Read.
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func (DirectoryFileDescriptionDefaultImpl) Read(ctx context.Context, dst usermem.IOSequence, opts ReadOptions) (int64, error) {
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return 0, syserror.EISDIR
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}
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// PWrite implements FileDescriptionImpl.PWrite.
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func (DirectoryFileDescriptionDefaultImpl) PWrite(ctx context.Context, src usermem.IOSequence, offset int64, opts WriteOptions) (int64, error) {
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return 0, syserror.EISDIR
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}
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// Write implements FileDescriptionImpl.Write.
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func (DirectoryFileDescriptionDefaultImpl) Write(ctx context.Context, src usermem.IOSequence, opts WriteOptions) (int64, error) {
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return 0, syserror.EISDIR
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}
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// DynamicBytesFileDescriptionImpl may be embedded by implementations of
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// FileDescriptionImpl that represent read-only regular files whose contents
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// are backed by a bytes.Buffer that is regenerated when necessary, consistent
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// with Linux's fs/seq_file.c:single_open().
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//
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// DynamicBytesFileDescriptionImpl.SetDataSource() must be called before first
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// use.
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type DynamicBytesFileDescriptionImpl struct {
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data DynamicBytesSource // immutable
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mu sync.Mutex // protects the following fields
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buf bytes.Buffer
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off int64
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lastRead int64 // offset at which the last Read, PRead, or Seek ended
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}
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// DynamicBytesSource represents a data source for a
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// DynamicBytesFileDescriptionImpl.
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type DynamicBytesSource interface {
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// Generate writes the file's contents to buf.
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Generate(ctx context.Context, buf *bytes.Buffer) error
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}
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// SetDataSource must be called exactly once on fd before first use.
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func (fd *DynamicBytesFileDescriptionImpl) SetDataSource(data DynamicBytesSource) {
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fd.data = data
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}
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// Preconditions: fd.mu must be locked.
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func (fd *DynamicBytesFileDescriptionImpl) preadLocked(ctx context.Context, dst usermem.IOSequence, offset int64, opts *ReadOptions) (int64, error) {
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// Regenerate the buffer if it's empty, or before pread() at a new offset.
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// Compare fs/seq_file.c:seq_read() => traverse().
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switch {
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case offset != fd.lastRead:
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fd.buf.Reset()
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fallthrough
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case fd.buf.Len() == 0:
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if err := fd.data.Generate(ctx, &fd.buf); err != nil {
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fd.buf.Reset()
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// fd.off is not updated in this case.
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fd.lastRead = 0
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return 0, err
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}
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}
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bs := fd.buf.Bytes()
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if offset >= int64(len(bs)) {
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return 0, io.EOF
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}
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n, err := dst.CopyOut(ctx, bs[offset:])
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fd.lastRead = offset + int64(n)
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return int64(n), err
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}
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// PRead implements FileDescriptionImpl.PRead.
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func (fd *DynamicBytesFileDescriptionImpl) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts ReadOptions) (int64, error) {
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fd.mu.Lock()
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n, err := fd.preadLocked(ctx, dst, offset, &opts)
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fd.mu.Unlock()
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return n, err
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}
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// Read implements FileDescriptionImpl.Read.
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func (fd *DynamicBytesFileDescriptionImpl) Read(ctx context.Context, dst usermem.IOSequence, opts ReadOptions) (int64, error) {
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fd.mu.Lock()
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n, err := fd.preadLocked(ctx, dst, fd.off, &opts)
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fd.off += n
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fd.mu.Unlock()
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return n, err
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}
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// Seek implements FileDescriptionImpl.Seek.
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func (fd *DynamicBytesFileDescriptionImpl) Seek(ctx context.Context, offset int64, whence int32) (int64, error) {
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fd.mu.Lock()
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defer fd.mu.Unlock()
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switch whence {
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case linux.SEEK_SET:
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// Use offset as given.
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case linux.SEEK_CUR:
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offset += fd.off
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default:
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// fs/seq_file:seq_lseek() rejects SEEK_END etc.
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return 0, syserror.EINVAL
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}
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if offset < 0 {
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return 0, syserror.EINVAL
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}
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if offset != fd.lastRead {
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// Regenerate the file's contents immediately. Compare
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// fs/seq_file.c:seq_lseek() => traverse().
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fd.buf.Reset()
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if err := fd.data.Generate(ctx, &fd.buf); err != nil {
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fd.buf.Reset()
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fd.off = 0
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fd.lastRead = 0
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return 0, err
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}
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fd.lastRead = offset
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}
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fd.off = offset
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return offset, nil
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}
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