Messages in this thread | | | Date | Mon, 9 Apr 2018 12:10:09 +0200 | From | Pali Rohár <> | Subject | Re: Race-free unlinking of directory entries |
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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@gmail.com
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