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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 fuse
import (
"io"
"math"
"sync"
"sync/atomic"
"gvisor.dev/gvisor/pkg/abi/linux"
"gvisor.dev/gvisor/pkg/context"
"gvisor.dev/gvisor/pkg/sentry/vfs"
"gvisor.dev/gvisor/pkg/syserror"
"gvisor.dev/gvisor/pkg/usermem"
)
type regularFileFD struct {
fileDescription
// off is the file offset.
off int64
// offMu protects off.
offMu sync.Mutex
}
// PRead implements vfs.FileDescriptionImpl.PRead.
func (fd *regularFileFD) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts vfs.ReadOptions) (int64, error) {
if offset < 0 {
return 0, syserror.EINVAL
}
// Check that flags are supported.
//
// TODO(gvisor.dev/issue/2601): Support select preadv2 flags.
if opts.Flags&^linux.RWF_HIPRI != 0 {
return 0, syserror.EOPNOTSUPP
}
size := dst.NumBytes()
if size == 0 {
// Early return if count is 0.
return 0, nil
} else if size > math.MaxUint32 {
// FUSE only supports uint32 for size.
// Overflow.
return 0, syserror.EINVAL
}
// TODO(gvisor.dev/issue/3678): Add direct IO support.
inode := fd.inode()
// Reading beyond EOF, update file size if outdated.
if uint64(offset+size) > atomic.LoadUint64(&inode.size) {
if err := inode.reviseAttr(ctx); err != nil {
return 0, err
}
// If the offset after update is still too large, return error.
if uint64(offset) >= atomic.LoadUint64(&inode.size) {
return 0, io.EOF
}
}
// Truncate the read with updated file size.
fileSize := atomic.LoadUint64(&inode.size)
if uint64(offset+size) > fileSize {
size = int64(fileSize) - offset
}
buffers, n, err := inode.fs.ReadInPages(ctx, fd, uint64(offset), uint32(size))
if err != nil {
return 0, err
}
// TODO(gvisor.dev/issue/3237): support indirect IO (e.g. caching),
// store the bytes that were read ahead.
// Update the number of bytes to copy for short read.
if n < uint32(size) {
size = int64(n)
}
// Copy the bytes read to the dst.
// This loop is intended for fragmented reads.
// For the majority of reads, this loop only execute once.
var copied int64
for _, buffer := range buffers {
toCopy := int64(len(buffer))
if copied+toCopy > size {
toCopy = size - copied
}
cp, err := dst.DropFirst64(copied).CopyOut(ctx, buffer[:toCopy])
if err != nil {
return 0, err
}
if int64(cp) != toCopy {
return 0, syserror.EIO
}
copied += toCopy
}
return copied, nil
}
// Read implements vfs.FileDescriptionImpl.Read.
func (fd *regularFileFD) Read(ctx context.Context, dst usermem.IOSequence, opts vfs.ReadOptions) (int64, error) {
fd.offMu.Lock()
n, err := fd.PRead(ctx, dst, fd.off, opts)
fd.off += n
fd.offMu.Unlock()
return n, err
}
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