On Thu, Mar 03, 2011 at 09:34:08AM -0500, Theodore Tso wrote:
>
> On Mar 2, 2011, at 10:24 PM, Al Viro wrote:
>
> > We have an interesting problem. Consider the following sequence
> > of syscalls:
> > mkdir("foo", 0777);
> > mkdir("bar", 0777);
> > fd1 = open("foo", O_DIRECTORY);
> > fd2 = open("bar", O_DIRECTORY);
> > rename("foo", "bar"); /* kill old bar */
>
> I must be missing something. I didn't think you could rename on
> top of a directory and have the directory disappear. Don't you get
> an error in that case? What happens if bar contains files?
ENOTEMPTY. Checked by ->rename() and yes, ext4 does that.
> We don't allow: mkdir("bar", 0777); unlink("bar");
>
> Why should this be any different?
Because it worked since 4.2BSD and got into POSIX. Replacing rename()
works; the only restrictions are
* you can't replace directory with non-directory
* you can't replace non-directory with directory
* directory being replaced shall be empty
* you can't replace a mountpoint or filesystem root
If the target is not busy, it is required to work. Whether it returns
-EBUSY for busy target is implementation-dependent and we allow that
for most of the filesystems.
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