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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 fs
import (
"io"
"sync/atomic"
"gvisor.dev/gvisor/pkg/secio"
"gvisor.dev/gvisor/pkg/sentry/context"
"gvisor.dev/gvisor/pkg/syserror"
)
// Splice moves data to this file, directly from another.
//
// Offsets are updated only if DstOffset and SrcOffset are set.
func Splice(ctx context.Context, dst *File, src *File, opts SpliceOpts) (int64, error) {
// Verify basic file flag permissions.
if !dst.Flags().Write || !src.Flags().Read {
return 0, syserror.EBADF
}
// Check whether or not the objects being sliced are stream-oriented
// (i.e. pipes or sockets). If yes, we elide checks and offset locks.
srcPipe := IsPipe(src.Dirent.Inode.StableAttr) || IsSocket(src.Dirent.Inode.StableAttr)
dstPipe := IsPipe(dst.Dirent.Inode.StableAttr) || IsSocket(dst.Dirent.Inode.StableAttr)
if !dstPipe && !opts.DstOffset && !srcPipe && !opts.SrcOffset {
switch {
case dst.UniqueID < src.UniqueID:
// Acquire dst first.
if !dst.mu.Lock(ctx) {
return 0, syserror.ErrInterrupted
}
defer dst.mu.Unlock()
if !src.mu.Lock(ctx) {
return 0, syserror.ErrInterrupted
}
defer src.mu.Unlock()
case dst.UniqueID > src.UniqueID:
// Acquire src first.
if !src.mu.Lock(ctx) {
return 0, syserror.ErrInterrupted
}
defer src.mu.Unlock()
if !dst.mu.Lock(ctx) {
return 0, syserror.ErrInterrupted
}
defer dst.mu.Unlock()
case dst.UniqueID == src.UniqueID:
// Acquire only one lock; it's the same file. This is a
// bit of a edge case, but presumably it's possible.
if !dst.mu.Lock(ctx) {
return 0, syserror.ErrInterrupted
}
defer dst.mu.Unlock()
}
// Use both offsets (locked).
opts.DstStart = dst.offset
opts.SrcStart = src.offset
} else if !dstPipe && !opts.DstOffset {
// Acquire only dst.
if !dst.mu.Lock(ctx) {
return 0, syserror.ErrInterrupted
}
defer dst.mu.Unlock()
opts.DstStart = dst.offset // Safe: locked.
} else if !srcPipe && !opts.SrcOffset {
// Acquire only src.
if !src.mu.Lock(ctx) {
return 0, syserror.ErrInterrupted
}
defer src.mu.Unlock()
opts.SrcStart = src.offset // Safe: locked.
}
// Check append-only mode and the limit.
if !dstPipe {
if dst.Flags().Append {
if opts.DstOffset {
// We need to acquire the lock.
if !dst.mu.Lock(ctx) {
return 0, syserror.ErrInterrupted
}
defer dst.mu.Unlock()
}
// Figure out the appropriate offset to use.
if err := dst.offsetForAppend(ctx, &opts.DstStart); err != nil {
return 0, err
}
}
// Enforce file limits.
limit, ok := dst.checkLimit(ctx, opts.DstStart)
switch {
case ok && limit == 0:
return 0, syserror.ErrExceedsFileSizeLimit
case ok && limit < opts.Length:
opts.Length = limit // Cap the write.
}
}
// Attempt to do a WriteTo; this is likely the most efficient.
//
// The underlying implementation may be able to donate buffers.
newOpts := SpliceOpts{
Length: opts.Length,
SrcStart: opts.SrcStart,
SrcOffset: !srcPipe,
Dup: opts.Dup,
DstStart: opts.DstStart,
DstOffset: !dstPipe,
}
n, err := src.FileOperations.WriteTo(ctx, src, dst, newOpts)
if n == 0 && err != nil {
// Attempt as a ReadFrom. If a WriteTo, a ReadFrom may also
// be more efficient than a copy if buffers are cached or readily
// available. (It's unlikely that they can actually be donate
n, err = dst.FileOperations.ReadFrom(ctx, dst, src, newOpts)
}
if n == 0 && err != nil {
// If we've failed up to here, and at least one of the sources
// is a pipe or socket, then we can't properly support dup.
// Return an error indicating that this operation is not
// supported.
if (srcPipe || dstPipe) && newOpts.Dup {
return 0, syserror.EINVAL
}
// We failed to splice the files. But that's fine; we just fall
// back to a slow path in this case. This copies without doing
// any mode changes, so should still be more efficient.
var (
r io.Reader
w io.Writer
)
fw := &lockedWriter{
Ctx: ctx,
File: dst,
}
if newOpts.DstOffset {
// Use the provided offset.
w = secio.NewOffsetWriter(fw, newOpts.DstStart)
} else {
// Writes will proceed with no offset.
w = fw
}
fr := &lockedReader{
Ctx: ctx,
File: src,
}
if newOpts.SrcOffset {
// Limit to the given offset and length.
r = io.NewSectionReader(fr, opts.SrcStart, opts.Length)
} else {
// Limit just to the given length.
r = &io.LimitedReader{fr, opts.Length}
}
// Copy between the two.
n, err = io.Copy(w, r)
}
// Update offsets, if required.
if n > 0 {
if !dstPipe && !opts.DstOffset {
atomic.StoreInt64(&dst.offset, dst.offset+n)
}
if !srcPipe && !opts.SrcOffset {
atomic.StoreInt64(&src.offset, src.offset+n)
}
}
return n, err
}
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