Re: git: 2a1d50fc12f6 - main - vfs_domount_update(): correct fsidcmp() usage

> On Dec 26, 2023, at 9:36 AM, Konstantin Belousov <kib@FreeBSD.org> wrote:
> 
> The branch main has been updated by kib:
> 
> URL: https://cgit.FreeBSD.org/src/commit/?id=2a1d50fc12f6e604da834fbaea961d412aae6e85
> 
> commit 2a1d50fc12f6e604da834fbaea961d412aae6e85
> Author:     Andrew Gierth <andrew@tao146.riddles.org.uk>
> AuthorDate: 2023-12-24 12:04:21 +0000
> Commit:     Konstantin Belousov <kib@FreeBSD.org>
> CommitDate: 2023-12-26 01:35:46 +0000
> 
>    vfs_domount_update(): correct fsidcmp() usage
> 
>    MFC after:      3 days
> ---
> sys/kern/vfs_mount.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/sys/kern/vfs_mount.c b/sys/kern/vfs_mount.c
> index 8e54c832e9f1..331e4887c200 100644
> --- a/sys/kern/vfs_mount.c
> +++ b/sys/kern/vfs_mount.c
> @@ -1388,7 +1388,7 @@ vfs_domount_update(
> 			error = EINVAL;
> 			goto end;
> 		}
> -		if (fsidcmp(&fsid_up, &mp->mnt_stat.f_fsid) != 0) {
> +		if (fsidcmp(fsid_up, &mp->mnt_stat.f_fsid) != 0) {
> 			error = ENOENT;
> 			goto end;
> 		}



I guess we want to ensure ` typeof(a) == typeof(b) == fsid_t `, to prevent such kind of error in future.

I see both gcc [1] and clang [2] have __builtin_types_compatible_p , so probably a good definition of fsidcmp should be

```
#define TYPEASSERT(v, t) \
	_Static_assert(__builtin_types_compatible_p(typeof(v), t), "Requires type '" #t "'")

#define fsidcmp(a, b) ({ \
	TYPEASSERT((a), fsid_t *); \
	TYPEASSERT((b), fsid_t *); \
	memcmp((a), (b), sizeof(fsid_t)); \
})
```

1. https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html
2. https://clang.llvm.org/docs/LanguageExtensions.html

Best regards,
Zhenlei