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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 gofer
import (
"sync"
"gvisor.dev/gvisor/pkg/abi/linux"
"gvisor.dev/gvisor/pkg/context"
"gvisor.dev/gvisor/pkg/fdnotifier"
"gvisor.dev/gvisor/pkg/safemem"
"gvisor.dev/gvisor/pkg/sentry/vfs"
"gvisor.dev/gvisor/pkg/syserror"
"gvisor.dev/gvisor/pkg/usermem"
"gvisor.dev/gvisor/pkg/waiter"
)
// specialFileFD implements vfs.FileDescriptionImpl for pipes, sockets, device
// special files, and (when filesystemOptions.specialRegularFiles is in effect)
// regular files. specialFileFD differs from regularFileFD by using per-FD
// handles instead of shared per-dentry handles, and never buffering I/O.
type specialFileFD struct {
fileDescription
// handle is used for file I/O. handle is immutable.
handle handle
// seekable is true if this file description represents a file for which
// file offset is significant, i.e. a regular file. seekable is immutable.
seekable bool
// mayBlock is true if this file description represents a file for which
// queue may send I/O readiness events. mayBlock is immutable.
mayBlock bool
queue waiter.Queue
// If seekable is true, off is the file offset. off is protected by mu.
mu sync.Mutex
off int64
}
func newSpecialFileFD(h handle, mnt *vfs.Mount, d *dentry, locks *vfs.FileLocks, flags uint32) (*specialFileFD, error) {
ftype := d.fileType()
seekable := ftype == linux.S_IFREG
mayBlock := ftype == linux.S_IFIFO || ftype == linux.S_IFSOCK
fd := &specialFileFD{
handle: h,
seekable: seekable,
mayBlock: mayBlock,
}
fd.LockFD.Init(locks)
if mayBlock && h.fd >= 0 {
if err := fdnotifier.AddFD(h.fd, &fd.queue); err != nil {
return nil, err
}
}
if err := fd.vfsfd.Init(fd, flags, mnt, &d.vfsd, &vfs.FileDescriptionOptions{
DenyPRead: !seekable,
DenyPWrite: !seekable,
}); err != nil {
if mayBlock && h.fd >= 0 {
fdnotifier.RemoveFD(h.fd)
}
return nil, err
}
return fd, nil
}
// Release implements vfs.FileDescriptionImpl.Release.
func (fd *specialFileFD) Release() {
if fd.mayBlock && fd.handle.fd >= 0 {
fdnotifier.RemoveFD(fd.handle.fd)
}
fd.handle.close(context.Background())
fs := fd.vfsfd.Mount().Filesystem().Impl().(*filesystem)
fs.syncMu.Lock()
delete(fs.specialFileFDs, fd)
fs.syncMu.Unlock()
}
// OnClose implements vfs.FileDescriptionImpl.OnClose.
func (fd *specialFileFD) OnClose(ctx context.Context) error {
if !fd.vfsfd.IsWritable() {
return nil
}
return fd.handle.file.flush(ctx)
}
// Readiness implements waiter.Waitable.Readiness.
func (fd *specialFileFD) Readiness(mask waiter.EventMask) waiter.EventMask {
if fd.mayBlock {
return fdnotifier.NonBlockingPoll(fd.handle.fd, mask)
}
return fd.fileDescription.Readiness(mask)
}
// EventRegister implements waiter.Waitable.EventRegister.
func (fd *specialFileFD) EventRegister(e *waiter.Entry, mask waiter.EventMask) {
if fd.mayBlock {
fd.queue.EventRegister(e, mask)
return
}
fd.fileDescription.EventRegister(e, mask)
}
// EventUnregister implements waiter.Waitable.EventUnregister.
func (fd *specialFileFD) EventUnregister(e *waiter.Entry) {
if fd.mayBlock {
fd.queue.EventUnregister(e)
return
}
fd.fileDescription.EventUnregister(e)
}
// PRead implements vfs.FileDescriptionImpl.PRead.
func (fd *specialFileFD) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts vfs.ReadOptions) (int64, error) {
if fd.seekable && offset < 0 {
return 0, syserror.EINVAL
}
// Check that flags are supported. Silently ignore RWF_HIPRI.
if opts.Flags&^linux.RWF_HIPRI != 0 {
return 0, syserror.EOPNOTSUPP
}
// Going through dst.CopyOutFrom() holds MM locks around file operations of
// unknown duration. For regularFileFD, doing so is necessary to support
// mmap due to lock ordering; MM locks precede dentry.dataMu. That doesn't
// hold here since specialFileFD doesn't client-cache data. Just buffer the
// read instead.
if d := fd.dentry(); d.fs.opts.interop != InteropModeShared {
d.touchAtime(fd.vfsfd.Mount())
}
buf := make([]byte, dst.NumBytes())
n, err := fd.handle.readToBlocksAt(ctx, safemem.BlockSeqOf(safemem.BlockFromSafeSlice(buf)), uint64(offset))
if err == syserror.EAGAIN {
err = syserror.ErrWouldBlock
}
if n == 0 {
return 0, err
}
if cp, cperr := dst.CopyOut(ctx, buf[:n]); cperr != nil {
return int64(cp), cperr
}
return int64(n), err
}
// Read implements vfs.FileDescriptionImpl.Read.
func (fd *specialFileFD) Read(ctx context.Context, dst usermem.IOSequence, opts vfs.ReadOptions) (int64, error) {
if !fd.seekable {
return fd.PRead(ctx, dst, -1, opts)
}
fd.mu.Lock()
n, err := fd.PRead(ctx, dst, fd.off, opts)
fd.off += n
fd.mu.Unlock()
return n, err
}
// PWrite implements vfs.FileDescriptionImpl.PWrite.
func (fd *specialFileFD) PWrite(ctx context.Context, src usermem.IOSequence, offset int64, opts vfs.WriteOptions) (int64, error) {
if fd.seekable && offset < 0 {
return 0, syserror.EINVAL
}
// Check that flags are supported. Silently ignore RWF_HIPRI.
if opts.Flags&^linux.RWF_HIPRI != 0 {
return 0, syserror.EOPNOTSUPP
}
if fd.seekable {
limit, err := vfs.CheckLimit(ctx, offset, src.NumBytes())
if err != nil {
return 0, err
}
src = src.TakeFirst64(limit)
}
// Do a buffered write. See rationale in PRead.
if d := fd.dentry(); d.fs.opts.interop != InteropModeShared {
d.touchCMtime()
}
buf := make([]byte, src.NumBytes())
// Don't do partial writes if we get a partial read from src.
if _, err := src.CopyIn(ctx, buf); err != nil {
return 0, err
}
n, err := fd.handle.writeFromBlocksAt(ctx, safemem.BlockSeqOf(safemem.BlockFromSafeSlice(buf)), uint64(offset))
if err == syserror.EAGAIN {
err = syserror.ErrWouldBlock
}
return int64(n), err
}
// Write implements vfs.FileDescriptionImpl.Write.
func (fd *specialFileFD) Write(ctx context.Context, src usermem.IOSequence, opts vfs.WriteOptions) (int64, error) {
if !fd.seekable {
return fd.PWrite(ctx, src, -1, opts)
}
fd.mu.Lock()
n, err := fd.PWrite(ctx, src, fd.off, opts)
fd.off += n
fd.mu.Unlock()
return n, err
}
// Seek implements vfs.FileDescriptionImpl.Seek.
func (fd *specialFileFD) Seek(ctx context.Context, offset int64, whence int32) (int64, error) {
if !fd.seekable {
return 0, syserror.ESPIPE
}
fd.mu.Lock()
defer fd.mu.Unlock()
newOffset, err := regularFileSeekLocked(ctx, fd.dentry(), fd.off, offset, whence)
if err != nil {
return 0, err
}
fd.off = newOffset
return newOffset, nil
}
// Sync implements vfs.FileDescriptionImpl.Sync.
func (fd *specialFileFD) Sync(ctx context.Context) error {
return fd.dentry().syncSharedHandle(ctx)
}
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