svn commit: r322969 - in head: sbin/mdconfig sys/dev/md sys/sys

[John Baldwin]

On Tuesday, August 29, 2017 12:18:18 PM Maxim Sobolev wrote:
> John, OK, maybe you are right and the current status quo was just an
> accident. I am curious what do you and other people think about expressing
> expected structure size and padding more explicitly instead of trying to
> accommodate for sometimes intricate play between alignment and type size
> with something like char[N]? I.e. along the following lines:
> 
> #if __WORDSIZE < 64

Use #ifdef __LP64__

> #define MD_IOCTL_LEN    436
> #else
> #define MD_IOCTL_LEN    448
> #endif
> 
> struct md_ioctl {
>     union {
>         struct _md_ioctl_payload {
>             unsigned        version;     /* Structure layout version */
>             unsigned        unit;        /* unit number */
>             enum md_types   type ;       /* type of disk */
>             char            *file;       /* pathname of file to mount */
>             off_t           mediasize;   /* size of disk in bytes */
>             unsigned        sectorsize;  /* sectorsize */
>             unsigned        options;     /* options */
>             u_int64_t       base;        /* base address */
>             int             fwheads;     /* firmware heads */
>             int             fwsectors;   /* firmware sectors */
>             char            *label;      /* label of the device */
>         } md;
>         char raw[MD_IOCTL_LEN]; /* payload + padding for future ideas */
>     };
> };
> CTASSERT(sizeof(struct md_ioctl) == MD_IOCTL_LEN);

This is not the style we use in other structures in FreeBSD.  Simply making
the existing MDNPAD depend on the #ifdef would be more consistent.  For a
really good example of how to handle padding, see kinfo_proc which has
separate "spare" arrays for int, long, void *, and char.

-- 
John Baldwin