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Avoid unnecessary slice allocation in usermem.BytesIO.blocksFromAddrRanges(). 

PiperOrigin-RevId: 280507239
This commit is contained in:
Jamie Liu 2019-11-14 14:03:24 -08:00 committed by gVisor bot
parent 3f7d937090
commit 9ca15dbf14
1 changed files with 26 additions and 11 deletions
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37
pkg/sentry/usermem/bytes_io.go
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@ -102,19 +102,34 @@ func (b *BytesIO) rangeCheck(addr Addr, length int) (int, error) {
}
func (b *BytesIO) blocksFromAddrRanges(ars AddrRangeSeq) (safemem.BlockSeq, error) {
blocks := make([]safemem.Block, 0, ars.NumRanges())
for !ars.IsEmpty() {
ar := ars.Head()
n, err := b.rangeCheck(ar.Start, int(ar.Length()))
if n != 0 {
blocks = append(blocks, safemem.BlockFromSafeSlice(b.Bytes[int(ar.Start):int(ar.Start)+n]))
switch ars.NumRanges() {
case 0:
return safemem.BlockSeq{}, nil
case 1:
block, err := b.blockFromAddrRange(ars.Head())
return safemem.BlockSeqOf(block), err
default:
blocks := make([]safemem.Block, 0, ars.NumRanges())
for !ars.IsEmpty() {
block, err := b.blockFromAddrRange(ars.Head())
if block.Len() != 0 {
blocks = append(blocks, block)
}
if err != nil {
return safemem.BlockSeqFromSlice(blocks), err
}
ars = ars.Tail()
}
if err != nil {
return safemem.BlockSeqFromSlice(blocks), err
}
ars = ars.Tail()
return safemem.BlockSeqFromSlice(blocks), nil
}
return safemem.BlockSeqFromSlice(blocks), nil
}
func (b *BytesIO) blockFromAddrRange(ar AddrRange) (safemem.Block, error) {
n, err := b.rangeCheck(ar.Start, int(ar.Length()))
if n == 0 {
return safemem.Block{}, err
}
return safemem.BlockFromSafeSlice(b.Bytes[int(ar.Start) : int(ar.Start)+n]), err
}
// BytesIOSequence returns an IOSequence representing the given byte slice.