linux-kernel - Re: [PATCH v3] err.h: allow IS_ERR_VALUE to handle properly more types

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Date:	Tue, 9 Feb 2016 01:44:06 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Andrzej Hajda <a.hajda@...sung.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	open list <linux-kernel@...r.kernel.org>,
	Bob Peterson <rpeterso@...hat.com>
Subject: Re: [PATCH v3] err.h: allow IS_ERR_VALUE to handle properly more
 types

On Mon, Feb 08, 2016 at 01:01:32PM +0100, Arnd Bergmann wrote:

> /git/arm-soc/fs/afs/write.c: In function 'afs_file_write':
> /git/arm-soc/fs/afs/write.c:646:201: error: call to '__compiletime_assert_646' declared with attribute error: IS_ERR_VALUE takes an unsigned argument
> make[4]: *** [fs/afs/write.o] Error 1
> make[4]: Target `__build' not remade because of errors.
> make[3]: *** [fs/afs] Error 2

... and taking a look at that code, we see this:
        if (IS_ERR_VALUE(result)) {
                _leave(" = %zd", result);
                return result;
        }

        _leave(" = %zd", result);
        return result;

Further grep for that shows e.g.
        /* determine the length of the filename */
        nlen = romfs_dev_strnlen(sb, pos + ROMFH_SIZE, ROMFS_MAXFN);
        if (IS_ERR_VALUE(nlen))
                goto eio;
which is also fucked in head, seeing that nlen should simply have been
int there, with check being if (nlen < 0).  But that would've been
insufficiently future-proof, I suppose - what if somebody wishes to modify
romfs to allow 2Gb-long file names?

For sarcasm-impaired: use of IS_ERR_VALUE turns out to be a nice red flag.
Often of the "I'm too lazy to check the calling conventions, let's gamble on
IS_ERR_VALUE doing no harm and to hell with whoever will be scratching head
reading the results" variety...