Fix ReadWithSizeAndUnlink on systems that have syscall based mmap

tools/utils/shm/shm.go

@@ -118,6 +118,7 @@ func read_till_buf_full(f *os.File, buf []byte) ([]byte, error) {
 			if len(p) == 0 && errors.Is(err, io.EOF) {
 				err = nil
 			}
+			err = fmt.Errorf("Failed to read from SHM file with error: %w", err)
 			return buf[:len(buf)-len(p)], err
 		}
 	}

tools/utils/shm/shm_syscall.go

@@ -4,6 +4,7 @@
 package shm
 
 import (
+	"encoding/binary"
 	"errors"
 	"fmt"
 	"io/fs"
@@ -182,17 +183,19 @@ func Open(name string, size uint64) (MMap, error) {
 }
 
 func ReadWithSizeAndUnlink(name string, file_callback ...func(*os.File) error) ([]byte, error) {
-	f, err := shm_open(name, os.O_RDONLY, 0)
+	mmap, err := Open(name, 4)
 	if err != nil {
 		return nil, err
 	}
-	defer f.Close()
+	size := uint64(binary.BigEndian.Uint32(mmap.Slice()))
-	defer shm_unlink(f.Name())
+	mmap.Close()
-	for _, cb := range file_callback {
+	mmap, err = Open(name, 4+size)
-		err = cb(f)
+	if err != nil {
-		if err != nil {
+		return nil, err
-			return nil, err
-		}
 	}
-	return read_with_size(f)
+	ans := make([]byte, size)
+	copy(ans, mmap.Slice()[4:])
+	mmap.Close()
+	mmap.Unlink()
+	return ans, nil
 }