netdev - Re: [PATCH v18 11/13] open: introduce openat2(2) syscall

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Message-ID: <20191217063950.5oqwwqz5p3bu7t2x@yavin.dot.cyphar.com>
Date:   Tue, 17 Dec 2019 17:39:50 +1100
From:   Aleksa Sarai <cyphar@...har.com>
To:     Florian Weimer <fweimer@...hat.com>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Jeff Layton <jlayton@...nel.org>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Arnd Bergmann <arnd@...db.de>,
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        Shuah Khan <shuah@...nel.org>,
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        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
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Subject: Re: [PATCH v18 11/13] open: introduce openat2(2) syscall

On 2019-12-16, Florian Weimer <fweimer@...hat.com> wrote:
> > diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h
> > index 1d338357df8a..58c3a0e543c6 100644
> > --- a/include/uapi/linux/fcntl.h
> > +++ b/include/uapi/linux/fcntl.h
> > @@ -93,5 +93,40 @@
> >  
> >  #define AT_RECURSIVE		0x8000	/* Apply to the entire subtree */
> >  
> > +/*
> > + * Arguments for how openat2(2) should open the target path. If @resolve is
> > + * zero, then openat2(2) operates very similarly to openat(2).
> > + *
> > + * However, unlike openat(2), unknown bits in @flags result in -EINVAL rather
> > + * than being silently ignored. @mode must be zero unless one of {O_CREAT,
> > + * O_TMPFILE} are set.
> > + *
> > + * @flags: O_* flags.
> > + * @mode: O_CREAT/O_TMPFILE file mode.
> > + * @resolve: RESOLVE_* flags.
> > + */
> > +struct open_how {
> > +	__aligned_u64 flags;
> > +	__u16 mode;
> > +	__u16 __padding[3]; /* must be zeroed */
> > +	__aligned_u64 resolve;
> > +};
> > +
> > +#define OPEN_HOW_SIZE_VER0	24 /* sizeof first published struct */
> > +#define OPEN_HOW_SIZE_LATEST	OPEN_HOW_SIZE_VER0
> > +
> > +/* how->resolve flags for openat2(2). */
> > +#define RESOLVE_NO_XDEV		0x01 /* Block mount-point crossings
> > +					(includes bind-mounts). */
> > +#define RESOLVE_NO_MAGICLINKS	0x02 /* Block traversal through procfs-style
> > +					"magic-links". */
> > +#define RESOLVE_NO_SYMLINKS	0x04 /* Block traversal through all symlinks
> > +					(implies OEXT_NO_MAGICLINKS) */
> > +#define RESOLVE_BENEATH		0x08 /* Block "lexical" trickery like
> > +					"..", symlinks, and absolute
> > +					paths which escape the dirfd. */
> > +#define RESOLVE_IN_ROOT		0x10 /* Make all jumps to "/" and ".."
> > +					be scoped inside the dirfd
> > +					(similar to chroot(2)). */
> >  
> >  #endif /* _UAPI_LINUX_FCNTL_H */
> 
> Would it be possible to move these to a new UAPI header?
> 
> In glibc, we currently do not #include <linux/fcntl.h>.  We need some of
> the AT_* constants in POSIX mode, and the header is not necessarily
> namespace-clean.  If there was a separate header for openat2 support, we
> could use that easily, and we would only have to maintain the baseline
> definitions (which never change).

Sure, (assuming nobody objects) I can move it to "linux/openat2.h".

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

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