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From:   ebiederm@xmission.com (Eric W. Biederman)
To:     Al Viro <viro@zeniv.linux.org.uk>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Jia He <justin.he@arm.com>, Petr Mladek <pmladek@suse.com>,
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        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Jonathan Corbet <corbet@lwn.net>,
        Al Viro <viro@ftp.linux.org.uk>,
        Heiko Carstens <hca@linux.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
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Date:   Mon, 10 May 2021 11:16:00 -0500
In-Reply-To: <YJdG8LhKBoFayOc+@zeniv-ca.linux.org.uk> (Al Viro's message of
        "Sun, 9 May 2021 02:20:32 +0000")
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Subject: Re: [PATCH RFC 1/3] fs: introduce helper d_path_fast()
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Al Viro <viro@zeniv.linux.org.uk> writes:
>
> Another thing that keeps bugging me about prepend_path() is the
> set of return values.  I mean, 0/1/2/3/-ENAMETOOLONG, and all
> except 0 are unlikely?  Might as well make that 0/1/2/3/-1, if
> not an outright 0/1/2/3/4.  And prepend() could return bool, while
> we are at it (true - success, false - overflow)...

I remember seeing that the different callers of prepend_path treated
those different cases differently.

But now that I look again the return value 3 (escaped) gets lumped
together with 2(detached).


On second look it appears that the two patterns that we actually have
are basically:

char *__d_path(const struct path *path,
	       const struct path *root,
	       char *buf, int buflen)
{
	error = prepend_path(path, root, &res, &buflen);

	if (error < 0)
		return ERR_PTR(error);
	if (error > 0)
		return NULL;
	return res;
}

char *d_absolute_path(const struct path *path,
	       char *buf, int buflen)
{
	error = prepend_path(path, &root, &res, &buflen);

	if (error > 1)
		error = -EINVAL;
	if (error < 0)
		return ERR_PTR(error);
	return res;
}

With d_absolute_path deciding that return value 1 absolute is not an
error.

That does look like there is plenty of room to refactor and make things
clearer.


Eric