Implement mmap for host fs in vfs2.

In VFS1, both fs/host and fs/gofer used the same utils for host file mappings.
Refactor parts of fsimpl/gofer to create similar utils to share with
fsimpl/host (memory accounting code moved to fsutil, page rounding arithmetic
moved to usermem).

Updates #1476.

PiperOrigin-RevId: 312345090

4 files changed, 12 insertions, 71 deletions

diff --git a/pkg/sentry/fsimpl/gofer/BUILD b/pkg/sentry/fsimpl/gofer/BUILD
index 5ce82b793..67e916525 100644
--- a/pkg/sentry/fsimpl/gofer/BUILD
+++ b/pkg/sentry/fsimpl/gofer/BUILD
@@ -36,7 +36,6 @@ go_library(
         "gofer.go",
         "handle.go",
         "p9file.go",
-        "pagemath.go",
         "regular_file.go",
         "socket.go",
         "special_file.go",
diff --git a/pkg/sentry/fsimpl/gofer/gofer.go b/pkg/sentry/fsimpl/gofer/gofer.go
index ebf063a58..6295f6b54 100644
--- a/pkg/sentry/fsimpl/gofer/gofer.go
+++ b/pkg/sentry/fsimpl/gofer/gofer.go
@@ -928,8 +928,8 @@ func (d *dentry) setStat(ctx context.Context, creds *auth.Credentials, stat *lin
 		// so we can't race with Write or another truncate.)
 		d.dataMu.Unlock()
 		if d.size < oldSize {
-			oldpgend := pageRoundUp(oldSize)
-			newpgend := pageRoundUp(d.size)
+			oldpgend, _ := usermem.PageRoundUp(oldSize)
+			newpgend, _ := usermem.PageRoundUp(d.size)
 			if oldpgend != newpgend {
 				d.mapsMu.Lock()
 				d.mappings.Invalidate(memmap.MappableRange{newpgend, oldpgend}, memmap.InvalidateOpts{
diff --git a/pkg/sentry/fsimpl/gofer/pagemath.go b/pkg/sentry/fsimpl/gofer/pagemath.go
deleted file mode 100644
index 847cb0784..000000000
--- a/pkg/sentry/fsimpl/gofer/pagemath.go
+++ /dev/null
@@ -1,31 +0,0 @@
-// 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 (
-	"gvisor.dev/gvisor/pkg/usermem"
-)
-
-// This are equivalent to usermem.Addr.RoundDown/Up, but without the
-// potentially truncating conversion to usermem.Addr. This is necessary because
-// there is no way to define generic "PageRoundDown/Up" functions in Go.
-
-func pageRoundDown(x uint64) uint64 {
-	return x &^ (usermem.PageSize - 1)
-}
-
-func pageRoundUp(x uint64) uint64 {
-	return pageRoundDown(x + usermem.PageSize - 1)
-}
diff --git a/pkg/sentry/fsimpl/gofer/regular_file.go b/pkg/sentry/fsimpl/gofer/regular_file.go
index 857f7c74e..0d10cf7ac 100644
--- a/pkg/sentry/fsimpl/gofer/regular_file.go
+++ b/pkg/sentry/fsimpl/gofer/regular_file.go
@@ -148,9 +148,9 @@ func (fd *regularFileFD) PWrite(ctx context.Context, src usermem.IOSequence, off
 			return 0, err
 		}
 		// Remove touched pages from the cache.
-		pgstart := pageRoundDown(uint64(offset))
-		pgend := pageRoundUp(uint64(offset + src.NumBytes()))
-		if pgend < pgstart {
+		pgstart := usermem.PageRoundDown(uint64(offset))
+		pgend, ok := usermem.PageRoundUp(uint64(offset + src.NumBytes()))
+		if !ok {
 			return 0, syserror.EINVAL
 		}
 		mr := memmap.MappableRange{pgstart, pgend}
@@ -306,9 +306,10 @@ func (rw *dentryReadWriter) ReadToBlocks(dsts safemem.BlockSeq) (uint64, error)
 			if fillCache {
 				// Read into the cache, then re-enter the loop to read from the
 				// cache.
+				gapEnd, _ := usermem.PageRoundUp(gapMR.End)
 				reqMR := memmap.MappableRange{
-					Start: pageRoundDown(gapMR.Start),
-					End:   pageRoundUp(gapMR.End),
+					Start: usermem.PageRoundDown(gapMR.Start),
+					End:   gapEnd,
 				}
 				optMR := gap.Range()
 				err := rw.d.cache.Fill(rw.ctx, reqMR, maxFillRange(reqMR, optMR), mf, usage.PageCache, rw.d.handle.readToBlocksAt)
@@ -671,7 +672,7 @@ func (d *dentry) Translate(ctx context.Context, required, optional memmap.Mappab
 
 	// Constrain translations to d.size (rounded up) to prevent translation to
 	// pages that may be concurrently truncated.
-	pgend := pageRoundUp(d.size)
+	pgend, _ := usermem.PageRoundUp(d.size)
 	var beyondEOF bool
 	if required.End > pgend {
 		if required.Start >= pgend {
@@ -818,43 +819,15 @@ type dentryPlatformFile struct {
 // IncRef implements platform.File.IncRef.
 func (d *dentryPlatformFile) IncRef(fr platform.FileRange) {
 	d.dataMu.Lock()
-	seg, gap := d.fdRefs.Find(fr.Start)
-	for {
-		switch {
-		case seg.Ok() && seg.Start() < fr.End:
-			seg = d.fdRefs.Isolate(seg, fr)
-			seg.SetValue(seg.Value() + 1)
-			seg, gap = seg.NextNonEmpty()
-		case gap.Ok() && gap.Start() < fr.End:
-			newRange := gap.Range().Intersect(fr)
-			usage.MemoryAccounting.Inc(newRange.Length(), usage.Mapped)
-			seg, gap = d.fdRefs.InsertWithoutMerging(gap, newRange, 1).NextNonEmpty()
-		default:
-			d.fdRefs.MergeAdjacent(fr)
-			d.dataMu.Unlock()
-			return
-		}
-	}
+	d.fdRefs.IncRefAndAccount(fr)
+	d.dataMu.Unlock()
 }
 
 // DecRef implements platform.File.DecRef.
 func (d *dentryPlatformFile) DecRef(fr platform.FileRange) {
 	d.dataMu.Lock()
-	seg := d.fdRefs.FindSegment(fr.Start)
-
-	for seg.Ok() && seg.Start() < fr.End {
-		seg = d.fdRefs.Isolate(seg, fr)
-		if old := seg.Value(); old == 1 {
-			usage.MemoryAccounting.Dec(seg.Range().Length(), usage.Mapped)
-			seg = d.fdRefs.Remove(seg).NextSegment()
-		} else {
-			seg.SetValue(old - 1)
-			seg = seg.NextSegment()
-		}
-	}
-	d.fdRefs.MergeAdjacent(fr)
+	d.fdRefs.DecRefAndAccount(fr)
 	d.dataMu.Unlock()
-
 }
 
 // MapInternal implements platform.File.MapInternal.