From: David Laight <David.Laight@ACULAB.COM>
To: 'NeilBrown' <neilb@suse.de>, "J. Bruce Fields" <bfields@fieldses.org>
Cc: "Andy Lutomirski" <luto@kernel.org>,
"Linus Torvalds" <torvalds@linux-foundation.org>,
"Eric W. Biederman" <ebiederm@xmission.com>,
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Subject: RE: [PATCH v1 0/7] Remove in-tree usage of MAP_DENYWRITE
Date: Fri, 20 Aug 2021 08:25:47 +0000 [thread overview]
Message-ID: <aacb44aad4064d4b84dca97c38d0b6a0@AcuMS.aculab.com> (raw)
In-Reply-To: <162943109106.9892.7426782042253067338@noble.neil.brown.name>
From: NeilBrown
> Sent: 20 August 2021 04:45
...
> O_DENYREAD is an insane flag. If a process reads a file that some other
> process is working on, then the only which could be hurt is the reader.
> So allowing a process to ask for the open to fail if someone is writing
> might make sense. Insisting that all opens fail does not.
> Any code wanting O_DENYREAD *should* use advisory locking, and any code
> wanting to know about read denial should too.
It might make sense if O_DENYREAD | O_DENYWRITE | O_RDWR are all set.
That would be what O_EXCL ought to mean for a normal file.
So would be useful for a program that wants to update a config file.
...
> It would be nice to be able to combine O_DENYWRITE with O_RDWR. This
> combination is exactly what the kernel *should* do for swap files.
I suspect that is a common usage - eg for updating a file that contains
a log file sequence number.
...
> I'm not sure about O_DENYDELETE. It is a lock on the name. Unix has
> traditionally used lock-files to lock a name. The functionality makes
> sense for processes with write-access to the directory...
I'm not sure it makes any sense on filesystems that use inode numbers.
Which name would you protect, and how would you manage to do the test.
On windows O_DENYDELETE is pretty much the default.
Which is why software updates are such a PITA.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2021-08-20 8:26 UTC|newest]
Thread overview: 82+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-12 8:43 [PATCH v1 0/7] Remove in-tree usage of MAP_DENYWRITE David Hildenbrand
2021-08-12 8:43 ` [PATCH v1 1/7] binfmt: don't use MAP_DENYWRITE when loading shared libraries via uselib() David Hildenbrand
2021-08-12 8:43 ` [PATCH v1 2/7] kernel/fork: factor out atomcially replacing the current MM exe_file David Hildenbrand
2021-08-12 9:17 ` Christian Brauner
2021-08-12 8:43 ` [PATCH v1 3/7] kernel/fork: always deny write access to " David Hildenbrand
2021-08-12 10:05 ` Christian Brauner
2021-08-12 10:13 ` David Hildenbrand
2021-08-12 12:32 ` Christian Brauner
2021-08-12 12:38 ` David Hildenbrand
2021-08-12 16:51 ` Linus Torvalds
2021-08-12 19:38 ` David Hildenbrand
2021-08-12 8:43 ` [PATCH v1 4/7] binfmt: remove in-tree usage of MAP_DENYWRITE David Hildenbrand
2021-08-12 8:43 ` [PATCH v1 5/7] mm: remove VM_DENYWRITE David Hildenbrand
2021-08-12 8:43 ` [PATCH v1 6/7] mm: ignore MAP_DENYWRITE in ksys_mmap_pgoff() David Hildenbrand
2021-08-12 8:43 ` [PATCH v1 7/7] fs: update documentation of get_write_access() and friends David Hildenbrand
2021-08-12 12:20 ` [PATCH v1 0/7] Remove in-tree usage of MAP_DENYWRITE Florian Weimer
2021-08-12 12:47 ` David Hildenbrand
2021-08-12 16:17 ` Eric W. Biederman
2021-08-12 17:32 ` Eric W. Biederman
2021-08-12 17:35 ` Andy Lutomirski
2021-08-12 17:48 ` Eric W. Biederman
2021-08-12 18:01 ` Andy Lutomirski
2021-08-12 18:10 ` Linus Torvalds
2021-08-12 18:47 ` Eric W. Biederman
2021-08-13 9:05 ` David Laight
[not found] ` <87h7ft2j68.fsf@disp2133>
2021-08-13 20:51 ` Florian Weimer
2021-08-14 0:31 ` Linus Torvalds
2021-08-14 0:49 ` Andy Lutomirski
2021-08-14 0:54 ` Linus Torvalds
2021-08-14 0:58 ` Linus Torvalds
2021-08-14 1:57 ` Al Viro
2021-08-14 2:02 ` Al Viro
2021-08-14 9:06 ` David Hildenbrand
2021-08-14 7:53 ` Christian Brauner
2021-08-14 19:52 ` David Laight
2021-08-26 17:48 ` Andy Lutomirski
2021-08-26 21:47 ` David Hildenbrand
2021-08-26 22:13 ` Eric W. Biederman
2021-08-27 8:22 ` David Laight
2021-08-27 15:58 ` Eric W. Biederman
2021-09-01 8:28 ` David Hildenbrand
2021-08-27 10:18 ` Christian Brauner
2021-08-14 3:04 ` Matthew Wilcox
2021-08-17 16:48 ` Removing Mandatory Locks Eric W. Biederman
2021-08-17 16:50 ` David Hildenbrand
2021-08-18 9:34 ` Rodrigo Campos
2021-08-19 19:18 ` Jeff Layton
2021-08-19 20:03 ` Willy Tarreau
2021-08-19 18:39 ` Jeff Layton
2021-08-19 19:15 ` Linus Torvalds
2021-08-19 19:55 ` Eric Biggers
2021-08-19 20:18 ` Jeff Layton
2021-08-19 20:31 ` Linus Torvalds
2021-08-19 21:43 ` Jeff Layton
2021-08-19 22:32 ` Linus Torvalds
2021-08-20 8:30 ` David Laight
2021-08-23 7:55 ` Geert Uytterhoeven
2021-08-23 8:14 ` David Laight
2021-08-20 13:43 ` Steven Rostedt
2021-08-20 16:06 ` Linus Torvalds
2021-08-20 2:10 ` Matthew Wilcox
2021-08-20 6:36 ` Amir Goldstein
2021-08-20 7:14 ` Amir Goldstein
2021-08-20 12:27 ` Jeff Layton
2021-08-20 12:38 ` Willy Tarreau
2021-08-20 13:03 ` Jeff Layton
2021-08-20 13:11 ` Willy Tarreau
2021-08-20 16:30 ` Kees Cook
2021-08-20 19:17 ` H. Peter Anvin
2021-08-20 21:29 ` Jeff Layton
2021-08-21 12:45 ` Jeff Layton
2021-08-23 22:15 ` J. Bruce Fields
2021-08-20 22:31 ` Matthew Wilcox
2021-08-18 7:51 ` [PATCH v1 0/7] Remove in-tree usage of MAP_DENYWRITE Christian Brauner
2021-08-18 15:42 ` J. Bruce Fields
2021-08-19 13:56 ` Eric W. Biederman
2021-08-19 14:33 ` J. Bruce Fields
2021-08-20 12:54 ` Jeff Layton
[not found] ` <162943109106.9892.7426782042253067338@noble.neil.brown.name>
2021-08-20 8:25 ` David Laight [this message]
2021-08-12 19:24 ` David Hildenbrand
2021-08-12 18:15 ` Florian Weimer
2021-08-12 18:21 ` Linus Torvalds
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