On Monday 09 April 2018 02:59:19 Christoph Hellwig wrote:
> On Mon, Apr 09, 2018 at 09:42:41AM +0200, Pali Rohár wrote:
> > Hi! I would like to remind this my older email about race free
> > unlinking. Is there any plan to provide such support?
>
> Given that in Linux we know which directory entry a given fd refers to,
> we shouldn't even need a new syscall, but simply support the
> AT_EMPTY_PATH flag for funlinkat.
I do not think it is enough, specially in cases when hard links are in
use. Example:
fd = open("/a")
link("/a", "/b")
link("/a", "/c")
unlink("/a")
And now I want to call funlink for "fd". Which file should be unlinked?
"/b" or "/c" or none or both?
Another example:
fd = open("/a")
link("/a", "/b")
unlink("/a")
Calling funlink for fd should unlink "/b" or it should fail?
And another example:
fd = open("/a")
rename("/a", "/b")
What should funlink do for fd now?
Note that there is difference which symlink is shown in /proc/<pid>/fd
between last two examples -- even those two examples results in the same
state (if there is no race). For last example <fd> points to "/b", for
previous <fd> points to "/a (deleted)".
--
Pali Rohár
pali.rohar@xxxxxxxxx
