From: Josh Triplett <email@example.com> To: "Darrick J. Wong" <firstname.lastname@example.org> Cc: "Theodore Y. Ts'o" <email@example.com>, Linus Torvalds <firstname.lastname@example.org>, Andreas Dilger <email@example.com>, Jan Kara <firstname.lastname@example.org>, Linux Kernel Mailing List <email@example.com>, firstname.lastname@example.org Subject: Re: ext4 regression in v5.9-rc2 from e7bfb5c9bb3d on ro fs with overlapped bitmaps Date: Fri, 9 Oct 2020 12:08:48 -0700 [thread overview] Message-ID: <20201009190848.GB4649@localhost> (raw) In-Reply-To: <20201009025409.GB6532@magnolia> On Thu, Oct 08, 2020 at 07:54:09PM -0700, Darrick J. Wong wrote: > On Thu, Oct 08, 2020 at 03:38:58PM -0700, Josh Triplett wrote: > > On Thu, Oct 08, 2020 at 10:54:48AM -0700, Darrick J. Wong wrote: > > > > > the head", and continued with the notion that anything other than > > > > > e2fsprogs making something to be mounted by mount(2) and handled by > > > > > fs/ext4 is being "inflicted", and if the goal didn't still seem to be > > > > > "how do we make it go away so that only e2fsprogs and the kernel ever > > > > > touch ext4". I started this thread because I'd written some userspace > > > > > code, a new version of the kernel made that userspace code stop working, > > > > > so I wanted to report that the moment I'd discovered that, along with a > > > > > potential way to address it with as little disrupton to ext4 as > > > > > possible. > > > > > > Ted: I don't think it's a good idea to make SHARED_BLOCKS disable block > > > validity checking by default. You could someday enable users to write > > > to block-sharing files by teaching ext4 how to COW, at which point you'd > > > need correct bitmaps and block validity to prevent accidental overwrite > > > of critical metadata. At that point you'd either be stuck with the > > > precedent that SHARED_BLOCKS implies noblock_validity, or you'd end up > > > breaking Josh's images again. > > > > That's a fair point (though I think a writable COW version of > > SHARED_BLOCKS would need a different flag). It'd make more sense to key > > this logic off of RO_COMPAT_READONLY or similar. But even better: > > It wouldn't require a new flag -- "rocompat" features bits mean that > "it's safe to allow userspace to read files off the disk if software > doesn't recognize this feature bit". Sure; I was more thinking that if that involved adding some data structures to track shared blocks and the need to COW, whatever mechanism that used might potentially need an incompat flag. > If someone /did/ add the code to write to files safely in the presence > of shared blocks, all they'd have to do to light up the functionality is > add it to the _SUPP define. Also, it's strange that the kernel source > doesn't even know of SHARED_BLOCKS, but that's also on Ted... It would be nice if the kernel's ext4.h header and e2fsprogs were fully in sync, yes. - Josh Triplett
next prev parent reply other threads:[~2020-10-09 19:09 UTC|newest] Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-10-04 23:17 Linux 5.9-rc8 Linus Torvalds 2020-10-05 8:14 ` ext4 regression in v5.9-rc2 from e7bfb5c9bb3d on ro fs with overlapped bitmaps Josh Triplett 2020-10-05 9:46 ` Jan Kara 2020-10-05 10:16 ` Josh Triplett 2020-10-05 16:19 ` Jan Kara 2020-10-05 16:20 ` Jan Kara 2020-10-05 17:36 ` Darrick J. Wong 2020-10-06 0:04 ` Theodore Y. Ts'o 2020-10-06 0:32 ` Josh Triplett 2020-10-06 2:51 ` Darrick J. Wong 2020-10-06 3:18 ` Theodore Y. Ts'o 2020-10-06 5:03 ` Josh Triplett 2020-10-06 6:03 ` Josh Triplett 2020-10-06 13:35 ` Theodore Y. Ts'o 2020-10-07 8:03 ` Josh Triplett 2020-10-07 14:32 ` Theodore Y. Ts'o 2020-10-07 20:14 ` Josh Triplett 2020-10-08 2:10 ` Theodore Y. Ts'o 2020-10-08 17:54 ` Darrick J. Wong 2020-10-08 22:38 ` Josh Triplett 2020-10-09 2:54 ` Darrick J. Wong 2020-10-09 19:08 ` Josh Triplett [this message] 2020-10-08 22:22 ` Josh Triplett 2020-10-09 14:37 ` Theodore Y. Ts'o 2020-10-09 20:30 ` Josh Triplett 2021-01-10 18:41 ` Malicious fs images was " Pavel Machek 2021-01-11 18:51 ` Darrick J. Wong 2021-01-11 19:39 ` Eric Biggers 2021-01-12 21:43 ` Theodore Ts'o 2021-01-12 22:28 ` Pavel Machek 2021-01-13 5:09 ` Theodore Ts'o 2020-10-08 2:57 ` Andreas Dilger 2020-10-08 19:12 ` Josh Triplett 2020-10-08 19:25 ` Andreas Dilger 2020-10-08 22:28 ` Josh Triplett
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