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From: Aleksa Sarai <asarai@suse.de>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: Aleksa Sarai <cyphar@cyphar.com>,
	Jeff Layton <jlayton@kernel.org>,
	"J. Bruce Fields" <bfields@fieldses.org>,
	Arnd Bergmann <arnd@arndb.de>,
	David Howells <dhowells@redhat.com>,
	Shuah Khan <shuah@kernel.org>,
	Shuah Khan <skhan@linuxfoundation.org>,
	Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	Yonghong Song <yhs@fb.com>, Andrii Nakryiko <andriin@fb.com>,
	Eric Biederman <ebiederm@xmission.com>,
	Andy Lutomirski <luto@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Kees Cook <keescook@chromium.org>, Jann Horn <jannh@google.com>,
	Tycho Andersen <tycho@tycho.ws>,
	David Drysdale <drysdale@google.com>,
	Chanho Min <chanho.min@lge.com>, Oleg Nesterov <oleg@redhat.com>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
	Christian Brauner <christian@brauner.io>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	dev@opencontainers.org, containers@lists.linux-foundation.org,
	bpf@vger.kernel.org, netdev@vger.kernel.org,
	linux-alpha@vger.kernel.org, linux-api@vger.kernel.org,
	libc-alpha@sourceware.org, linux-arch@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-fsdevel@vger.kernel.org, linux-ia64@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
	linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org,
	linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
	linux-s390@vger.kernel.org, linux-sh@vger.kernel.org,
	linux-xtensa@linux-xtensa.org, sparclinux@vger.kernel.org
Subject: Re: [PATCH v16 02/12] namei: allow nd_jump_link() to produce errors
Date: Sun, 17 Nov 2019 05:09:34 +1100	[thread overview]
Message-ID: <20191116180934.fajrkc4jqcewiuqd@yavin.dot.cyphar.com> (raw)
In-Reply-To: <20191116003702.GX26530@ZenIV.linux.org.uk>

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On 2019-11-16, Al Viro <viro@zeniv.linux.org.uk> wrote:
> On Sat, Nov 16, 2019 at 11:27:52AM +1100, Aleksa Sarai wrote:
> > +	error = nd_jump_link(&path);
> > +	if (error)
> > +		path_put(&path);
> 
> > +	error = nd_jump_link(&ns_path);
> > +	if (error)
> > +		path_put(&ns_path);
> 
> > +	error = nd_jump_link(&path);
> > +	if (error)
> > +		path_put(&path);
> 
> 3 calls.  Exact same boilerplate in each to handle a failure case.
> Which spells "wrong calling conventions"; it's absolutely clear
> that we want that path_put() inside nd_jump_link().
> 
> The rule should be this: reference that used to be held in
> *path is consumed in any case.  On success it goes into
> nd->path, on error it's just dropped, but in any case, the
> caller has the same refcounting environment to deal with.
> 
> If you need the same boilerplate cleanup on failure again and again,
> the calling conventions are wrong and need to be fixed.

Will do.

> And I'm not sure that int is the right return type here, to be honest.
> void * might be better - return ERR_PTR() or NULL, so that the value
> could be used as return value of ->get_link() that calls that thing.

I don't agree, given that the few callers of ns_get_path() are
inconsistent with regards to whether they should use IS_ERR() or check
for NULL, not to mention that "void *error" reads to me as being very
odd given how common "int error" is throughout the kernel. There's also
the "error == ERR_PTR(-EAGAIN)" checks which also read as being quite
odd too.

But the main motivating factor for changing it was that the one use
where "void *" is useful (proc_ns_get_link) becomes needlessly ugly
because of the "nd_jump_link() can return errors" change:

	error = ERR_PTR(nd_jump_link(&ns_path));

Or probably (if you don't want to rely on ERR_PTR(0) == NULL):

	int err = nd_jump_link(&ns_path);
	if (err)
		error = ERR_PTR(err);

-- 
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>

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  parent reply	other threads:[~2019-11-16 18:10 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-16  0:27 [PATCH v16 00/12] open: introduce openat2(2) syscall Aleksa Sarai
2019-11-16  0:27 ` Aleksa Sarai
2019-11-16  0:27 ` [PATCH v16 01/12] nsfs: clean-up ns_get_path() signature to return int Aleksa Sarai
2019-11-16  0:27   ` Aleksa Sarai
2019-11-16  0:27 ` [PATCH v16 02/12] namei: allow nd_jump_link() to produce errors Aleksa Sarai
2019-11-16  0:27   ` Aleksa Sarai
2019-11-16  0:37   ` Al Viro
2019-11-16  0:37     ` Al Viro
2019-11-16 18:09     ` Aleksa Sarai [this message]
2019-11-16 18:09       ` Aleksa Sarai
2019-11-16  0:27 ` [PATCH v16 03/12] namei: allow set_root() " Aleksa Sarai
2019-11-16  0:27   ` Aleksa Sarai
2019-11-16  0:27 ` [PATCH v16 04/12] namei: LOOKUP_NO_SYMLINKS: block symlink resolution Aleksa Sarai
2019-11-16  0:27   ` Aleksa Sarai
2019-11-16  0:27 ` [PATCH v16 05/12] namei: LOOKUP_NO_MAGICLINKS: block magic-link resolution Aleksa Sarai
2019-11-16  0:27   ` Aleksa Sarai
2019-11-16  0:27 ` [PATCH v16 06/12] namei: LOOKUP_NO_XDEV: block mountpoint crossing Aleksa Sarai
2019-11-16  0:27   ` Aleksa Sarai
2019-11-16  0:27 ` [PATCH v16 07/12] namei: LOOKUP_BENEATH: O_BENEATH-like scoped resolution Aleksa Sarai
2019-11-16  0:27   ` Aleksa Sarai
2019-11-16  0:27 ` [PATCH v16 08/12] namei: LOOKUP_IN_ROOT: chroot-like " Aleksa Sarai
2019-11-16  0:27   ` Aleksa Sarai
2019-11-16  0:27 ` [PATCH v16 09/12] namei: LOOKUP_{IN_ROOT,BENEATH}: permit limited ".." resolution Aleksa Sarai
2019-11-16  0:27   ` Aleksa Sarai
2019-11-16  0:28 ` [PATCH v16 10/12] open: introduce openat2(2) syscall Aleksa Sarai
2019-11-16  0:28   ` Aleksa Sarai
2019-11-16  0:28 ` [PATCH v16 11/12] selftests: add openat2(2) selftests Aleksa Sarai
2019-11-16  0:28   ` Aleksa Sarai
2019-11-16  0:28 ` [PATCH v16 12/12] Documentation: path-lookup: include new LOOKUP flags Aleksa Sarai
2019-11-16  0:28   ` Aleksa Sarai

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