linux-kernel - Re: [PATCH 11/11] ext4: add cross rename support

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Date:	Fri, 17 Jan 2014 23:53:07 +1300
From:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:	Miklos Szeredi <miklos@...redi.hu>
CC:	mtk.manpages@...il.com, "J. Bruce Fields" <bfields@...ldses.org>,
	Jan Kara <jack@...e.cz>, Al Viro <viro@...iv.linux.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Howells <dhowells@...hat.com>,
	Zach Brown <zab@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	"mszeredi@...e.cz" <mszeredi@...e.cz>
Subject: Re: [PATCH 11/11] ext4: add cross rename support

Hi Miklos,

A few comments below, including one piece in the code that really must be fixed.

On 01/16/2014 11:54 PM, Miklos Szeredi wrote:
>> On Wed, Jan 15, 2014 at 7:23 PM, J. Bruce Fields <bfields@...ldses.org> wrote:
>>> Do you have a man page update somewhere for the two new flags?
> 
> Here's the updated man page (and attached the patch)
> 
> Michael, could you please review the interface?
> 
> I forgot to CC you when posing the patch series.  I can resend it if you want,
> or you can fetch the latest version of the cross-rename series from:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs.git cross-rename

[...]

>        renameat2()  has an additional flags argument.  renameat2() call with a
>        zero flags argument is equivalent to renameat().
> 
>        The flags argument is a bitfield consisting of zero or more of the fol-
>        lowing constants defined in <linux/fs.h>:
> 
>        RENAME_NOREPLACE
>               Don't  overwrite  the  target of the rename.  Return an error if
>               the target would be overwritten.
> 
>        RENAME_EXCHANGE
>               Atomically exchange the source and destination.  Both must exist
>               but  may  be of a different type (e.g. one a non-empty directory
>               and the other a symbolic link).

Somewhere here it would be good to explain the consequences if

   (flags & (RENAME_NOREPLACE | RENAME_EXCHANGE)) == 
                   (RENAME_NOREPLACE | RENAME_EXCHANGE)

Okay -- it's EINVAL, but here the man page text should say something like
"these two flags can't be specified together", right?

> RETURN VALUE
>        On success, renameat() and renameat2()  return  0.   On  error,  -1  is
>        returned and errno is set to indicate the error.
> 
> ERRORS
>        The  same errors that occur for rename(2) can also occur for renameat()
>        and  renameat2().   The  following  additional  errors  can  occur  for
>        renameat() and renameat2():
> 
>        EBADF  olddirfd or newdirfd is not a valid file descriptor.
> 
>        ENOTDIR
>               oldpath  is relative and olddirfd is a file descriptor referring
>               to a file other than a directory; or  similar  for  newpath  and
>               newdirfd
> 
>        The following additional errors are defined for renameat2():
> 
>        EOPNOTSUPP
>               The filesystem does not support a flag in flags

This is not the usual error for an invalid bit flag. Please make it EINVAL.
(See the man pages for the *at() calls that have a 'flags" argument.)

>        EINVAL Invalid combination of flags

(This is okay.)

Looks otherwise okay to me (and I agree with Bruce's comments).

Cheers,

Michael



-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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