3 files changed, 142 insertions, 7 deletions
diff --git a/pkg/sentry/memmap/file_range.go b/pkg/sentry/memmap/file_range.go
new file mode 100644
index 000000000..e4c852a66
--- /dev/null
+++ b/pkg/sentry/memmap/file_range.go
@@ -0,0 +1,62 @@
+package memmap
+
+// A Range represents a contiguous range of T.
+//
+// +stateify savable
+type FileRange struct {
+	// Start is the inclusive start of the range.
+	Start uint64
+
+	// End is the exclusive end of the range.
+	End uint64
+}
+
+// WellFormed returns true if r.Start <= r.End. All other methods on a Range
+// require that the Range is well-formed.
+func (r FileRange) WellFormed() bool {
+	return r.Start <= r.End
+}
+
+// Length returns the length of the range.
+func (r FileRange) Length() uint64 {
+	return r.End - r.Start
+}
+
+// Contains returns true if r contains x.
+func (r FileRange) Contains(x uint64) bool {
+	return r.Start <= x && x < r.End
+}
+
+// Overlaps returns true if r and r2 overlap.
+func (r FileRange) Overlaps(r2 FileRange) bool {
+	return r.Start < r2.End && r2.Start < r.End
+}
+
+// IsSupersetOf returns true if r is a superset of r2; that is, the range r2 is
+// contained within r.
+func (r FileRange) IsSupersetOf(r2 FileRange) bool {
+	return r.Start <= r2.Start && r.End >= r2.End
+}
+
+// Intersect returns a range consisting of the intersection between r and r2.
+// If r and r2 do not overlap, Intersect returns a range with unspecified
+// bounds, but for which Length() == 0.
+func (r FileRange) Intersect(r2 FileRange) FileRange {
+	if r.Start < r2.Start {
+		r.Start = r2.Start
+	}
+	if r.End > r2.End {
+		r.End = r2.End
+	}
+	if r.End < r.Start {
+		r.End = r.Start
+	}
+	return r
+}
+
+// CanSplitAt returns true if it is legal to split a segment spanning the range
+// r at x; that is, splitting at x would produce two ranges, both of which have
+// non-zero length.
+func (r FileRange) CanSplitAt(x uint64) bool {
+	return r.Contains(x) && r.Start < x
+}
diff --git a/pkg/sentry/memmap/memmap.go b/pkg/sentry/memmap/memmap.go
index c6db9fc8f..c188f6c29 100644
--- a/pkg/sentry/memmap/memmap.go
+++ b/pkg/sentry/memmap/memmap.go
@@ -19,12 +19,12 @@ import (
 	"fmt"
 
 	"gvisor.dev/gvisor/pkg/context"
-	"gvisor.dev/gvisor/pkg/sentry/platform"
+	"gvisor.dev/gvisor/pkg/safemem"
 	"gvisor.dev/gvisor/pkg/usermem"
 )
 
 // Mappable represents a memory-mappable object, a mutable mapping from uint64
-// offsets to (platform.File, uint64 File offset) pairs.
+// offsets to (File, uint64 File offset) pairs.
 //
 // See mm/mm.go for Mappable's place in the lock order.
 //
@@ -74,7 +74,7 @@ type Mappable interface {
 	// Translations are valid until invalidated by a callback to
 	// MappingSpace.Invalidate or until the caller removes its mapping of the
 	// translated range. Mappable implementations must ensure that at least one
-	// reference is held on all pages in a platform.File that may be the result
+	// reference is held on all pages in a File that may be the result
 	// of a valid Translation.
 	//
 	// Preconditions: required.Length() > 0. optional.IsSupersetOf(required).
@@ -100,7 +100,7 @@ type Translation struct {
 	Source MappableRange
 
 	// File is the mapped file.
-	File platform.File
+	File File
 
 	// Offset is the offset into File at which this Translation begins.
 	Offset uint64
@@ -110,9 +110,9 @@ type Translation struct {
 	Perms usermem.AccessType
 }
 
-// FileRange returns the platform.FileRange represented by t.
-func (t Translation) FileRange() platform.FileRange {
-	return platform.FileRange{t.Offset, t.Offset + t.Source.Length()}
+// FileRange returns the FileRange represented by t.
+func (t Translation) FileRange() FileRange {
+	return FileRange{t.Offset, t.Offset + t.Source.Length()}
 }
 
 // CheckTranslateResult returns an error if (ts, terr) does not satisfy all
@@ -361,3 +361,49 @@ type MMapOpts struct {
 	// TODO(jamieliu): Replace entirely with MappingIdentity?
 	Hint string
 }
+
+// File represents a host file that may be mapped into an platform.AddressSpace.
+type File interface {
+	// All pages in a File are reference-counted.
+
+	// IncRef increments the reference count on all pages in fr.
+	//
+	// Preconditions: fr.Start and fr.End must be page-aligned. fr.Length() >
+	// 0. At least one reference must be held on all pages in fr. (The File
+	// interface does not provide a way to acquire an initial reference;
+	// implementors may define mechanisms for doing so.)
+	IncRef(fr FileRange)
+
+	// DecRef decrements the reference count on all pages in fr.
+	//
+	// Preconditions: fr.Start and fr.End must be page-aligned. fr.Length() >
+	// 0. At least one reference must be held on all pages in fr.
+	DecRef(fr FileRange)
+
+	// MapInternal returns a mapping of the given file offsets in the invoking
+	// process' address space for reading and writing.
+	//
+	// Note that fr.Start and fr.End need not be page-aligned.
+	//
+	// Preconditions: fr.Length() > 0. At least one reference must be held on
+	// all pages in fr.
+	//
+	// Postconditions: The returned mapping is valid as long as at least one
+	// reference is held on the mapped pages.
+	MapInternal(fr FileRange, at usermem.AccessType) (safemem.BlockSeq, error)
+
+	// FD returns the file descriptor represented by the File.
+	//
+	// The only permitted operation on the returned file descriptor is to map
+	// pages from it consistent with the requirements of AddressSpace.MapFile.
+	FD() int
+}
+
+// FileRange represents a range of uint64 offsets into a File.
+//
+// type FileRange <generated using go_generics>
+
+// String implements fmt.Stringer.String.
+func (fr FileRange) String() string {
+	return fmt.Sprintf("[%#x, %#x)", fr.Start, fr.End)
+}
diff --git a/pkg/sentry/memmap/memmap_state_autogen.go b/pkg/sentry/memmap/memmap_state_autogen.go
index d7cd50786..4feb2eb66 100644
--- a/pkg/sentry/memmap/memmap_state_autogen.go
+++ b/pkg/sentry/memmap/memmap_state_autogen.go
@@ -6,6 +6,32 @@ import (
 	"gvisor.dev/gvisor/pkg/state"
 )
 
+func (x *FileRange) StateTypeName() string {
+	return "pkg/sentry/memmap.FileRange"
+}
+
+func (x *FileRange) StateFields() []string {
+	return []string{
+		"Start",
+		"End",
+	}
+}
+
+func (x *FileRange) beforeSave() {}
+
+func (x *FileRange) StateSave(m state.Sink) {
+	x.beforeSave()
+	m.Save(0, &x.Start)
+	m.Save(1, &x.End)
+}
+
+func (x *FileRange) afterLoad() {}
+
+func (x *FileRange) StateLoad(m state.Source) {
+	m.Load(0, &x.Start)
+	m.Load(1, &x.End)
+}
+
 func (x *MappableRange) StateTypeName() string {
 	return "pkg/sentry/memmap.MappableRange"
 }
@@ -62,6 +88,7 @@ func (x *MappingOfRange) StateLoad(m state.Source) {
 }
 
 func init() {
+	state.Register((*FileRange)(nil))
 	state.Register((*MappableRange)(nil))
 	state.Register((*MappingOfRange)(nil))
 }