Daniel Phillips  writes:
> ...or:

quoted text
>

>  	if (IS_ERR(buffer = blockread(inode->map, block)))

>  		return PTR_ERR(buffer);

>

> Anybody have an opinion on whether IS_ERR works just as well in user

> space as in kernel?

It would work if kernel reserved that range as kernel space like linux.

Well, if we want to make sure it, I think we can reserve the address

range for it.
e.g. maybe
	error_base = mmap(,MAX_ERRNO + 1,PROT_NONE,,,);
        ERR_PTR(err)

        	assert(err < 0);

                return error_base + -err;
	PTR_ERR(ptr)

        	return -(long)(ptr - error_base);
	IS_ERR(ptr)

        	return (error_base < ptr && ptr <= error_base + MAX_ERRNO);

--

OGAWA Hirofumi 
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