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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 fsutil
import (
"math"
"sync"
"gvisor.googlesource.com/gvisor/pkg/sentry/context"
"gvisor.googlesource.com/gvisor/pkg/sentry/fs"
"gvisor.googlesource.com/gvisor/pkg/sentry/memmap"
"gvisor.googlesource.com/gvisor/pkg/sentry/platform"
"gvisor.googlesource.com/gvisor/pkg/sentry/safemem"
"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
)
// HostMappable implements memmap.Mappable and platform.File over a
// CachedFileObject.
//
// Lock order (compare the lock order model in mm/mm.go):
// truncateMu ("fs locks")
// mu ("memmap.Mappable locks not taken by Translate")
// ("platform.File locks")
// backingFile ("CachedFileObject locks")
//
// +stateify savable
type HostMappable struct {
hostFileMapper *HostFileMapper
backingFile CachedFileObject
mu sync.Mutex `state:"nosave"`
// mappings tracks mappings of the cached file object into
// memmap.MappingSpaces so it can invalidated upon save. Protected by mu.
mappings memmap.MappingSet
// truncateMu protects writes and truncations. See Truncate() for details.
truncateMu sync.RWMutex `state:"nosave"`
}
// NewHostMappable creates a new mappable that maps directly to host FD.
func NewHostMappable(backingFile CachedFileObject) *HostMappable {
return &HostMappable{
hostFileMapper: NewHostFileMapper(),
backingFile: backingFile,
}
}
// AddMapping implements memmap.Mappable.AddMapping.
func (h *HostMappable) AddMapping(ctx context.Context, ms memmap.MappingSpace, ar usermem.AddrRange, offset uint64, writable bool) error {
// Hot path. Avoid defers.
h.mu.Lock()
mapped := h.mappings.AddMapping(ms, ar, offset, writable)
for _, r := range mapped {
h.hostFileMapper.IncRefOn(r)
}
h.mu.Unlock()
return nil
}
// RemoveMapping implements memmap.Mappable.RemoveMapping.
func (h *HostMappable) RemoveMapping(ctx context.Context, ms memmap.MappingSpace, ar usermem.AddrRange, offset uint64, writable bool) {
// Hot path. Avoid defers.
h.mu.Lock()
unmapped := h.mappings.RemoveMapping(ms, ar, offset, writable)
for _, r := range unmapped {
h.hostFileMapper.DecRefOn(r)
}
h.mu.Unlock()
}
// CopyMapping implements memmap.Mappable.CopyMapping.
func (h *HostMappable) CopyMapping(ctx context.Context, ms memmap.MappingSpace, srcAR, dstAR usermem.AddrRange, offset uint64, writable bool) error {
return h.AddMapping(ctx, ms, dstAR, offset, writable)
}
// Translate implements memmap.Mappable.Translate.
func (h *HostMappable) Translate(ctx context.Context, required, optional memmap.MappableRange, at usermem.AccessType) ([]memmap.Translation, error) {
return []memmap.Translation{
{
Source: optional,
File: h,
Offset: optional.Start,
Perms: usermem.AnyAccess,
},
}, nil
}
// InvalidateUnsavable implements memmap.Mappable.InvalidateUnsavable.
func (h *HostMappable) InvalidateUnsavable(ctx context.Context) error {
h.mu.Lock()
h.mappings.InvalidateAll(memmap.InvalidateOpts{})
h.mu.Unlock()
return nil
}
// MapInternal implements platform.File.MapInternal.
func (h *HostMappable) MapInternal(fr platform.FileRange, at usermem.AccessType) (safemem.BlockSeq, error) {
return h.hostFileMapper.MapInternal(fr, h.backingFile.FD(), at.Write)
}
// FD implements platform.File.FD.
func (h *HostMappable) FD() int {
return h.backingFile.FD()
}
// IncRef implements platform.File.IncRef.
func (h *HostMappable) IncRef(fr platform.FileRange) {
mr := memmap.MappableRange{Start: fr.Start, End: fr.End}
h.hostFileMapper.IncRefOn(mr)
}
// DecRef implements platform.File.DecRef.
func (h *HostMappable) DecRef(fr platform.FileRange) {
mr := memmap.MappableRange{Start: fr.Start, End: fr.End}
h.hostFileMapper.DecRefOn(mr)
}
// Truncate truncates the file, invalidating any mapping that may have been
// removed after the size change.
//
// Truncation and writes are synchronized to prevent races where writes make the
// file grow between truncation and invalidation below:
// T1: Calls SetMaskedAttributes and stalls
// T2: Appends to file causing it to grow
// T2: Writes to mapped pages and COW happens
// T1: Continues and wronly invalidates the page mapped in step above.
func (h *HostMappable) Truncate(ctx context.Context, newSize int64) error {
h.truncateMu.Lock()
defer h.truncateMu.Unlock()
mask := fs.AttrMask{Size: true}
attr := fs.UnstableAttr{Size: newSize}
if err := h.backingFile.SetMaskedAttributes(ctx, mask, attr); err != nil {
return err
}
// Invalidate COW mappings that may exist beyond the new size in case the file
// is being shrunk. Other mappings don't need to be invalidated because
// translate will just return identical mappings after invalidation anyway,
// and SIGBUS will be raised and handled when the mappings are touched.
//
// Compare Linux's mm/truncate.c:truncate_setsize() =>
// truncate_pagecache() =>
// mm/memory.c:unmap_mapping_range(evencows=1).
h.mu.Lock()
defer h.mu.Unlock()
mr := memmap.MappableRange{
Start: fs.OffsetPageEnd(newSize),
End: fs.OffsetPageEnd(math.MaxInt64),
}
h.mappings.Invalidate(mr, memmap.InvalidateOpts{InvalidatePrivate: true})
return nil
}
// Allocate reserves space in the backing file.
func (h *HostMappable) Allocate(ctx context.Context, offset int64, length int64) error {
h.truncateMu.RLock()
err := h.backingFile.Allocate(ctx, offset, length)
h.truncateMu.RUnlock()
return err
}
// Write writes to the file backing this mappable.
func (h *HostMappable) Write(ctx context.Context, src usermem.IOSequence, offset int64) (int64, error) {
h.truncateMu.RLock()
n, err := src.CopyInTo(ctx, &writer{ctx: ctx, hostMappable: h, off: offset})
h.truncateMu.RUnlock()
return n, err
}
type writer struct {
ctx context.Context
hostMappable *HostMappable
off int64
}
// WriteFromBlocks implements safemem.Writer.WriteFromBlocks.
func (w *writer) WriteFromBlocks(src safemem.BlockSeq) (uint64, error) {
n, err := w.hostMappable.backingFile.WriteFromBlocksAt(w.ctx, src, uint64(w.off))
w.off += int64(n)
return n, err
}
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