From: Al Viro <viro@zeniv.linux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Omar Sandoval <osandov@osandov.com>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
linux-btrfs <linux-btrfs@vger.kernel.org>,
Linux API <linux-api@vger.kernel.org>,
Kernel Team <kernel-team@fb.com>
Subject: Re: [PATCH RESEND x3 v9 1/9] iov_iter: add copy_struct_from_iter()
Date: Fri, 18 Jun 2021 19:42:41 +0000 [thread overview]
Message-ID: <YMz3MfgmbtTSQljy@zeniv-ca.linux.org.uk> (raw)
In-Reply-To: <CAHk-=whRA=54dtO3ha-C2-fV4XQ2nry99BmfancW-16EFGTHVg@mail.gmail.com>
On Fri, Jun 18, 2021 at 11:50:25AM -0700, Linus Torvalds wrote:
> I think that you may need it to be based on Al's series for that to
> work, which might be inconvenient, though.
>
> One other non-code issue: particularly since you only handle a subset
> of the iov_iter cases, it would be nice to have an explanation for
> _why_ those particular cases.
>
> IOW, have some trivial explanation for each of the cases. "iovec" is
> for regular read/write, what triggers the kvec and bvec cases?
>
> But also, the other way around. Why doesn't the pipe case trigger? No
> splice support?
Pipe ones are strictly destinations - they can't be sources. So if you
see it called for one of those, you've a bug.
Xarray ones are *not* - they can be sources, and that's missing here.
Much more unpleasant, though, is that this thing has hard dependency on
nr_seg == 1 *AND* openly suggests the use of iov_iter_single_seg_count(),
which is completely wrong. That sucker has some weird users left (as
of #work.iov_iter), but all of them are actually due to API deficiencies
and I very much hope to kill that thing off.
Why not simply add iov_iter_check_zeroes(), that would be called after
copy_from_iter() and verified that all that's left in the iterator
consists of zeroes? Then this copy_struct_from_...() would be
trivial to express through those two. And check_zeroes would also
be trivial, especially on top of #work.iov_iter. With no calls of
iov_iter_advance() at all, while we are at it...
IDGI... Omar, what semantics do you really want from that primitive?
next prev parent reply other threads:[~2021-06-18 19:42 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 [this message]
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
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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