Re: CVS commit: src/sys/dev

[Paul Goyette <paul%whooppee.com@localhost>]

On Sat, 24 Apr 2021, Robert Elz wrote:

>    Date:        Sat, 24 Apr 2021 00:15:37 +0000
>    From:        "Michael Lorenz" <macallan%netbsd.org@localhost>
>    Message-ID:  <20210424001537.C5C83FA95%cvs.NetBSD.org@localhost>
>
>  | add an ioctl() to get a list of fonts currently available via wsfont
>
> It seems to me it would be useful for that ioctl to copyout()
> the fi_numentries field of the struct (if addr != NULL) from
> wsdisplayio_listfonts() just before the ENOMEM check (so it is
> updated, even if ENOMEM is returned).   (Does it make any sense
> for addr to be NULL, or should that be an error?  EINVAL or something.)
>
> Otherwise, there doesn't seem to be any easy way for the user of
> the ioctl to know how many fonts were returned (checking which elements
> of the array were modified is not "easy") or how big the buffer would
> need to be to fetch all of them in the ENOMEM case.

In several other places, we return "total space needed" separately,
regardless of how much data was actually copied.  The general paradigm
is (more or less)

	buff = NULL;
	size = 0;
	err = func(..., buff, size, &need);
	while (err == 0) {
		if (need > size) {
			free(buff);
			buff = malloc(need);
			if (buff == NULL)
				err = ENOMEM;

		}
	}

For a real-life example look at the modctl(2) code for MODULE_STAT



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