From: Omar Sandoval <firstname.lastname@example.org>
To: Linus Torvalds <email@example.com>
Cc: Matthew Wilcox <firstname.lastname@example.org>,
"Martin K. Petersen" <email@example.com>,
Al Viro <firstname.lastname@example.org>,
Dave Chinner <email@example.com>,
Linux API <firstname.lastname@example.org>,
Kernel Team <email@example.com>,
Dave Chinner <firstname.lastname@example.org>
Subject: Re: [PATCH RESEND x3 v9 1/9] iov_iter: add copy_struct_from_iter()
Date: Fri, 25 Jun 2021 14:07:59 -0700 [thread overview]
Message-ID: <YNZFr7oJj1nkrwJY@relinquished.localdomain> (raw)
On Fri, Jun 25, 2021 at 09:16:15AM -0700, Linus Torvalds wrote:
> On Thu, Jun 24, 2021 at 8:38 PM Matthew Wilcox <email@example.com> wrote:
> > Does it make any kind of sense to talk about doing this for buffered I/O,
> > given that we can't generate them for (eg) mmaped files?
> Sure we can.
> Or rather, some people might very well like to do it even for mutable
> data. In fact, _especially_ for mutable data.
> You might want to do things like "write out the state I verified just
> a moment ago", and if it has changed since then, you *want* the result
> to be invalid because the checksums no longer match - in case somebody
> else changed the data you used for the state calculation and
> verification in the meantime. It's very much why you'd want a separate
> checksum in the first place.
> Yeah, yeah, you can - and people do - just do things like this with a
> separate checksum. But if you know that the filesystem has internal
> checksumming support _anyway_, you might want to use it, and basically
> say "use this checksum, if the data doesn't match when I read it back
> I want to get an IO error".
> (The "data doesn't match" _could_ be just due to DRAM corruption etc,
> of course. Some people care about things like that. You want
> "verified" filesystem contents - it might not be about security, it
> might simply be about "I have validated this data and if it's not the
> same data any more it's useless and I need to re-generate it").
> Am I a big believer in this model? No. Portability concerns (across
> OS'es, across filesystems, even just across backups on the same exact
> system) means that even if we did this, very few people would use it.
> People who want this end up using an external checksum instead and do
> it outside of and separately from the actual IO, because then they can
> do it on existing systems.
> So my argument is not "we want this". My argument is purely that some
> buffered filesystem IO case isn't actually any different from the
> traditional "I want access to the low-level sector hardware checksum
> data". The use cases are basically exactly the same.
> Of course, basically nobody does that hw sector checksum either, for
> all the same reasons, even if it's been around for decades.
> So my "checksum metadata interface" is not something I'm a big
> believer in, but I really don't think it's really all _that_ different
> from the whole "compressed format interface" that this whole patch
> series is about. They are pretty much the same thing in many ways.
I see the similarity in the sense that we basically want to pass some
extra metadata down with the read or write. So then do we want to add
preadv3/pwritev3 for encoded I/O now so that checksums can use it in the
future? The encoding metadata could go in this "struct io_how", either
directly or in a separate structure with a pointer in "struct io_how".
It could get messy with compat syscalls.
next prev parent reply other threads:[~2021-06-25 21:08 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-17 23:51 [PATCH RESEND x3 v9 0/9] fs: interface for directly reading/writing compressed data Omar Sandoval
2021-06-17 23:51 ` [PATCH RESEND x3 v9 1/9] iov_iter: add copy_struct_from_iter() Omar Sandoval
2021-06-18 18:50 ` Linus Torvalds
2021-06-18 19:42 ` Al Viro
2021-06-18 19:49 ` Al Viro
2021-06-18 20:33 ` Omar Sandoval
2021-06-18 20:32 ` Omar Sandoval
2021-06-18 20:58 ` Al Viro
2021-06-18 21:10 ` Linus Torvalds
2021-06-18 21:32 ` Al Viro
2021-06-18 21:40 ` Linus Torvalds
2021-06-18 22:10 ` Omar Sandoval
2021-06-18 22:32 ` Al Viro
2021-06-19 0:43 ` Omar Sandoval
2021-06-21 18:46 ` Omar Sandoval
2021-06-21 19:33 ` Linus Torvalds
2021-06-21 20:46 ` Omar Sandoval
2021-06-21 20:53 ` Omar Sandoval
2021-06-21 20:55 ` Omar Sandoval
2021-06-22 22:06 ` Dave Chinner
2021-06-23 17:49 ` Omar Sandoval
2021-06-23 18:28 ` Linus Torvalds
2021-06-23 19:33 ` Omar Sandoval
2021-06-23 19:45 ` Al Viro
2021-06-23 20:46 ` Omar Sandoval
2021-06-23 21:39 ` Al Viro
2021-06-23 21:58 ` Omar Sandoval
2021-06-23 22:26 ` Al Viro
2021-06-24 2:00 ` Matthew Wilcox
2021-06-24 6:14 ` Omar Sandoval
2021-06-24 17:52 ` Linus Torvalds
2021-06-24 18:28 ` Omar Sandoval
2021-06-24 21:07 ` Linus Torvalds
2021-06-24 22:41 ` Martin K. Petersen
2021-06-25 3:38 ` Matthew Wilcox
2021-06-25 16:16 ` Linus Torvalds
2021-06-25 21:07 ` Omar Sandoval [this message]
2021-07-07 17:59 ` Omar Sandoval
2021-07-19 15:44 ` Josef Bacik
2021-06-24 6:41 ` Christoph Hellwig
2021-06-24 7:50 ` Omar Sandoval
2021-06-18 22:14 ` Al Viro
2021-06-17 23:51 ` [PATCH RESEND x3 v9 2/9] fs: add O_ALLOW_ENCODED open flag Omar Sandoval
2021-06-17 23:51 ` [PATCH RESEND x3 v9 3/9] fs: add RWF_ENCODED for reading/writing compressed data Omar Sandoval
2021-06-17 23:51 ` [PATCH RESEND x3 v9 4/9] btrfs: don't advance offset for compressed bios in btrfs_csum_one_bio() Omar Sandoval
2021-06-17 23:51 ` [PATCH RESEND x3 v9 5/9] btrfs: add ram_bytes and offset to btrfs_ordered_extent Omar Sandoval
2021-06-17 23:51 ` [PATCH RESEND x3 v9 6/9] btrfs: support different disk extent size for delalloc Omar Sandoval
2021-06-17 23:51 ` [PATCH RESEND x3 v9 7/9] btrfs: optionally extend i_size in cow_file_range_inline() Omar Sandoval
2021-06-17 23:51 ` [PATCH RESEND x3 v9 8/9] btrfs: implement RWF_ENCODED reads Omar Sandoval
2021-06-17 23:51 ` [PATCH RESEND x3 v9 9/9] btrfs: implement RWF_ENCODED writes Omar Sandoval
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