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Re: [PATCH] Add renameat2 function [BZ #17662]
- From: Yury Norov <ynorov at caviumnetworks dot com>
- To: Florian Weimer <fweimer at redhat dot com>
- Cc: libc-alpha at sourceware dot org, Alexander Viro <viro at zeniv dot linux dot org dot uk>, linux-kernel at vger dot kernel dot org, linux-fsdevel at vger dot kernel dot org, linux-api at vger dot kernel dot org
- Date: Mon, 2 Jul 2018 11:46:22 +0300
- Subject: Re: [PATCH] Add renameat2 function [BZ #17662]
- References: <20180630121447.E4C8643994575@oldenburg.str.redhat.com> <20180701214901.GA32498@yury-thinkpad> <60505ccf-a399-6320-74f5-e2e17965d25c@redhat.com>
+ Alexander Viro <viro@zeniv.linux.org.uk>, kernel maillists.
On Mon, Jul 02, 2018 at 08:48:36AM +0200, Florian Weimer wrote:
> On 07/01/2018 11:49 PM, Yury Norov wrote:
>
> > > +#ifdef __USE_GNU
> > > +/* Flags for renameat. */
> >
> > Flags for renameat2, right?
>
> Thanks, fixed.
>
> > > +# define RENAME_NOREPLACE (1 << 0)
> > > +# define RENAME_EXCHANGE (1 << 1)
> > > +# define RENAME_WHITEOUT (1 << 2)
> >
> > I really don't understand how it works. Could you / somebody explain me?
> >
> > include/uapi/linux/fs.h in kernel sources already defines this flags,
> > and this file is usually available in Linux distribution. So I don't
> > understand what for it is duplicated here. If you keep in mind
> > old linux headers or non-linux systems, I think it should be protected
> > with #ifndef guards.
>
> <linux/fs.h> undefines and defines macros not mentioned in the standards
> (and it even contains a few unrelated structs), so we cannot include it
> without _GNU_SOURCE.
>
> It might be possible to include it only for _GNU_SOURCE, but there are a
> lot of things in <linux/fs.h>, so that does not seem to be particularly
> advisable.
>
> We still support building glibc with 3.2 kernel headers, and if the
> definitions you quoted above are not available, building the test case
> would fail.
Is my understanding correct that glibc community finds <linux/fs.h>
inappropriate for their use, and prefer to re-introduce (duplicate)
its functionality locally? I think it's wrong. The right way to go
is to make kernel headers comfortable for users instead of ignoring
it.
Are you OK to switch to kernel RENAME_* definitions if they will be
located in separated small file? Like in the patch below.
Signed-off-by: Yury Norov <ynorov@caviumnetworks.com>
---
include/uapi/linux/fs.h | 4 +---
include/uapi/linux/rename.h | 12 ++++++++++++
2 files changed, 13 insertions(+), 3 deletions(-)
create mode 100644 include/uapi/linux/rename.h
diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
index c27576d471c2..46c03ea31a76 100644
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -44,9 +44,7 @@
#define SEEK_HOLE 4 /* seek to the next hole */
#define SEEK_MAX SEEK_HOLE
-#define RENAME_NOREPLACE (1 << 0) /* Don't overwrite target */
-#define RENAME_EXCHANGE (1 << 1) /* Exchange source and dest */
-#define RENAME_WHITEOUT (1 << 2) /* Whiteout source */
+#include <linux/rename.h>
struct file_clone_range {
__s64 src_fd;
diff --git a/include/uapi/linux/rename.h b/include/uapi/linux/rename.h
new file mode 100644
index 000000000000..7178f0565657
--- /dev/null
+++ b/include/uapi/linux/rename.h
@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef _UAPI_LINUX_RENAME_H
+#define _UAPI_LINUX_RENAME_H
+
+/*
+ * Definitions for rename syscall family.
+ */
+#define RENAME_NOREPLACE (1 << 0) /* Don't overwrite target */
+#define RENAME_EXCHANGE (1 << 1) /* Exchange source and dest */
+#define RENAME_WHITEOUT (1 << 2) /* Whiteout source */
+
+#endif /* _UAPI_LINUX_RENAME_H */
--
2.17.1