[Libguestfs] [libnbd PATCH 4/7] Revert "generator/Go.ml: Simplify copy_uint32_array"

This reverts commit 6725fa0e129f9a60d7b89707ef8604e0aeeeaf43, although with a more modern style. Casting a C array to a Go slice just to benefit from potential optimizations in Go's copy(), is rather complex to understand, especially when we are still copying things (the main reason to treat a C array as a Go slice is when avoiding a copy has a benefit). Without a benchmark showing measurable difference in runtime speed, and considering that network transit time probably dominates the time spent on block status and its callback, it is not worth the complexity. Furthermore, an upcoming patch wants to add a similar helper function for converting between a list of C and Go structs, where the copy() trick will not work; and having the two helpers look alike is beneficial. Suggested-by: Laszlo Ersek <lersek(a)redhat.com&gt; CC: Nir Soffer <nsoffer(a)redhat.com&gt; Signed-off-by: Eric Blake <eblake(a)redhat.com&gt; --- generator/GoLang.ml | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-) diff --git a/generator/GoLang.ml b/generator/GoLang.ml index 0aa83bdc..77dacadb 100644 --- a/generator/GoLang.ml +++ b/generator/GoLang.ml @@ -509,12 +509,14 @@ let /* Closures. */ -func copy_uint32_array (entries *C.uint32_t, count C.size_t) []uint32 { - ret := make([]uint32, int (count)) - // See https://github.com/golang/go/wiki/cgo#turning-c-arrays-into-go-slices - // TODO: Use unsafe.Slice() when we require Go 1.17. - s := (*[1<<30]uint32)(unsafe.Pointer(entries))[:count:count] - copy(ret, s) +func copy_uint32_array(entries *C.uint32_t, count C.size_t) []uint32 { + ret := make([]uint32, int(count)) + addr := uintptr(unsafe.Pointer(entries)) + for i := 0; i < int(count); i++ { + ptr := (*C.uint32_t)(unsafe.Pointer(addr)) + ret[i] = uint32(*ptr) + addr += unsafe.Sizeof(*ptr) + } return ret } "; base-commit: 5c2fc3cc7e14146d000b65b191e70d9a0585a395 prerequisite-patch-id: 4db98f7b211c0de9a4095b300970e1973cf0716c prerequisite-patch-id: 0bb320af5109c1c21e5b76d44e6ec1e7e685fd9f prerequisite-patch-id: 205525d8ea09e77ea13f43d0720153ed5904dbcd -- 2.41.0