Using fcntl() based fallocate on darwin doesnt work with file descriptors returned by shm_open

kitty/shm.py

@@ -82,7 +82,10 @@ class SharedMemory:
         self._name = name
         try:
             if flags & os.O_CREAT and size:
-                os.posix_fallocate(self._fd, 0, size)
+                if hasattr(os, 'posix_fallocate'):
+                    os.posix_fallocate(self._fd, 0, size)
+                else:
+                    os.ftruncate(self._fd, size)
             self.stats = os.fstat(self._fd)
             size = self.stats.st_size
             self._mmap = mmap.mmap(self._fd, size, access=mmap.ACCESS_READ if readonly else mmap.ACCESS_WRITE)

tools/utils/shm/fallocate_darwin.go

@@ -1,29 +0,0 @@
-// License: GPLv3 Copyright: 2023, Kovid Goyal, <kovid at kovidgoyal.net>
-
-package shm
-
-import (
-	"errors"
-	"fmt"
-	"syscall"
-	"unsafe"
-
-	"golang.org/x/sys/unix"
-)
-
-var _ = fmt.Print
-
-func Fallocate_simple(fd int, size int64) (err error) {
-	store := &syscall.Fstore_t{
-		Flags:   syscall.F_ALLOCATEALL,
-		Posmode: syscall.F_PEOFPOSMODE,
-		Offset:  0,
-		Length:  size,
-	}
-
-	for {
-		if _, _, err = syscall.Syscall(syscall.SYS_FCNTL, uintptr(fd), syscall.F_PREALLOCATE, uintptr(unsafe.Pointer(store))); !errors.Is(err, unix.EINTR) {
-			return err
-		}
-	}
-}

tools/utils/shm/fallocate_other.go

@@ -1,6 +1,6 @@
 // License: GPLv3 Copyright: 2023, Kovid Goyal, <kovid at kovidgoyal.net>
 
-//go:build !darwin && !linux
+//go:build !linux
 
 package shm
 

tools/utils/shm/shm_test.go

@@ -16,7 +16,7 @@ import (
 var _ = fmt.Print
 
 func TestSHM(t *testing.T) {
-	force_use_of_fallocate = runtime.GOOS == "darwin" || runtime.GOOS == "linux"
+	force_use_of_fallocate = runtime.GOOS == "linux"
 	defer func() { force_use_of_fallocate = false }()
 	data := make([]byte, 13347)
 	_, _ = rand.Read(data)