Add Read/Write to the MMap interface

tools/utils/shm/shm.go

@@ -53,6 +53,9 @@ type MMap interface {
 	FileSystemName() string
 	Stat() (fs.FileInfo, error)
 	Flush() error
+	Seek(offset int64, whence int) (ret int64, err error)
+	Read(b []byte) (n int, err error)
+	Write(b []byte) (n int, err error)
 }
 
 type AccessFlags int
@@ -106,9 +109,11 @@ func truncate_or_unlink(ans *os.File, size uint64) (err error) {
 
 const NUM_BYTES_FOR_SIZE = 4
 
+var ErrRegionTooSmall = errors.New("mmaped region too small")
+
 func WriteWithSize(self MMap, b []byte, at int) error {
 	if len(self.Slice()) < at+len(b)+NUM_BYTES_FOR_SIZE {
-		return io.ErrShortBuffer
+		return ErrRegionTooSmall
 	}
 	binary.BigEndian.PutUint32(self.Slice()[at:], uint32(len(b)))
 	copy(self.Slice()[at+NUM_BYTES_FOR_SIZE:], b)
@@ -118,12 +123,12 @@ func WriteWithSize(self MMap, b []byte, at int) error {
 func ReadWithSize(self MMap, at int) ([]byte, error) {
 	s := self.Slice()[at:]
 	if len(s) < NUM_BYTES_FOR_SIZE {
-		return nil, io.ErrShortBuffer
+		return nil, ErrRegionTooSmall
 	}
 	size := int(binary.BigEndian.Uint32(self.Slice()[at : at+NUM_BYTES_FOR_SIZE]))
 	s = s[NUM_BYTES_FOR_SIZE:]
 	if len(s) < size {
-		return nil, io.ErrShortBuffer
+		return nil, ErrRegionTooSmall
 	}
 	return s[:size], nil
 }
@@ -158,6 +163,41 @@ func ReadWithSizeAndUnlink(name string, file_callback ...func(fs.FileInfo) error
 	return ans, nil
 }
 
+func Read(self MMap, b []byte) (n int, err error) {
+	pos, _ := self.Seek(0, io.SeekCurrent)
+	if pos < 0 {
+		pos = 0
+	}
+	s := self.Slice()
+	sz := int64(len(s))
+	if pos >= sz {
+		return 0, io.EOF
+	}
+	n = copy(b, s[pos:])
+	self.Seek(int64(n), io.SeekCurrent)
+	return
+}
+
+func Write(self MMap, b []byte) (n int, err error) {
+	if len(b) == 0 {
+		return 0, nil
+	}
+	pos, _ := self.Seek(0, io.SeekCurrent)
+	if pos < 0 {
+		pos = 0
+	}
+	s := self.Slice()
+	if pos >= int64(len(s)) {
+		return 0, io.ErrShortWrite
+	}
+	n = copy(s[pos:], b)
+	self.Seek(int64(n), io.SeekCurrent)
+	if n < len(b) {
+		return n, io.ErrShortWrite
+	}
+	return n, nil
+}
+
 func test_integration_with_python(args []string) (rc int, err error) {
 	switch args[0] {
 	default:

tools/utils/shm/shm_fs.go

@@ -7,6 +7,7 @@ import (
 	"crypto/sha256"
 	"errors"
 	"fmt"
+	"io"
 	"io/fs"
 	"os"
 	"path/filepath"
@@ -21,6 +22,7 @@ var _ = fmt.Print
 
 type file_based_mmap struct {
 	f            *os.File
+	pos          int64
 	region       []byte
 	unlinked     bool
 	special_name string
@@ -42,6 +44,26 @@ func file_mmap(f *os.File, size uint64, access AccessFlags, truncate bool, speci
 	return &file_based_mmap{f: f, region: region, special_name: special_name}, nil
 }
 
+func (self *file_based_mmap) Seek(offset int64, whence int) (ret int64, err error) {
+	switch whence {
+	case io.SeekStart:
+		self.pos = offset
+	case os.SEEK_END:
+		self.pos = int64(len(self.region)) + offset
+	case os.SEEK_CUR:
+		self.pos += offset
+	}
+	return self.pos, nil
+}
+
+func (self *file_based_mmap) Read(b []byte) (n int, err error) {
+	return Read(self, b)
+}
+
+func (self *file_based_mmap) Write(b []byte) (n int, err error) {
+	return Write(self, b)
+}
+
 func (self *file_based_mmap) Stat() (fs.FileInfo, error) {
 	return self.f.Stat()
 }

tools/utils/shm/shm_syscall.go

@@ -6,6 +6,7 @@ package shm
 import (
 	"errors"
 	"fmt"
+	"io"
 	"io/fs"
 	"os"
 	"strings"
@@ -65,6 +66,7 @@ func shm_open(name string, flags, perm int) (ans *os.File, err error) {
 
 type syscall_based_mmap struct {
 	f        *os.File
+	pos      int64
 	region   []byte
 	unlinked bool
 }
@@ -117,6 +119,26 @@ func (self *syscall_based_mmap) Unlink() (err error) {
 	return shm_unlink(self.Name())
 }
 
+func (self *syscall_based_mmap) Seek(offset int64, whence int) (ret int64, err error) {
+	switch whence {
+	case io.SeekStart:
+		self.pos = offset
+	case os.SEEK_END:
+		self.pos = int64(len(self.region)) + offset
+	case os.SEEK_CUR:
+		self.pos += offset
+	}
+	return self.pos, nil
+}
+
+func (self *syscall_based_mmap) Read(b []byte) (n int, err error) {
+	return Read(self, b)
+}
+
+func (self *syscall_based_mmap) Write(b []byte) (n int, err error) {
+	return Write(self, b)
+}
+
 func (self *syscall_based_mmap) IsFileSystemBacked() bool { return false }
 func (self *syscall_based_mmap) FileSystemName() string   { return "" }