From: Omar Sandoval <osandov@osandov.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
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>,
Dave Chinner <dchinner@redhat.com>
Subject: Re: [PATCH RESEND x3 v9 1/9] iov_iter: add copy_struct_from_iter()
Date: Mon, 21 Jun 2021 13:55:03 -0700 [thread overview]
Message-ID: <YND8p7ioQRfoWTOU@relinquished.localdomain> (raw)
In-Reply-To: <YND6jOrku2JDgqjt@relinquished.localdomain>
On Mon, Jun 21, 2021 at 01:46:04PM -0700, Omar Sandoval wrote:
> On Mon, Jun 21, 2021 at 12:33:17PM -0700, Linus Torvalds wrote:
> > On Mon, Jun 21, 2021 at 11:46 AM Omar Sandoval <osandov@osandov.com> wrote:
> > >
> > > How do we get the userspace size with the encoded_iov.size approach?
> > > We'd have to read the size from the iov_iter before writing to the rest
> > > of the iov_iter. Is it okay to mix the iov_iter as a source and
> > > destination like this? From what I can tell, it's not intended to be
> > > used like this.
> >
> > I guess it could work that way, but yes, it's ugly as hell. And I
> > really don't want a readv() system call - that should write to the
> > result buffer - to first have to read from it.
> >
> > So I think the original "just make it be the first iov entry" is the
> > better approach, even if Al hates it.
> >
> > Although I still get the feeling that using an ioctl is the *really*
> > correct way to go. That was my first reaction to the series
> > originally, and I still don't see why we'd have encoded data in a
> > regular read/write path.
> >
> > What was the argument against ioctl's, again?
>
> The suggestion came from Dave Chinner here:
> https://lore.kernel.org/linux-fsdevel/20190905021012.GL7777@dread.disaster.area/
>
> His objection to an ioctl was two-fold:
>
> 1. This interfaces looks really similar to normal read/write, so we
> should try to use the normal read/write interface for it. Perhaps
> this trouble with iov_iter has refuted that.
> 2. The last time we had Btrfs-specific ioctls that eventually became
> generic (FIDEDUPERANGE and FICLONE{,RANGE}), the generalization was
> painful. Part of the problem with clone/dedupe was that the Btrfs
> ioctls were underspecified. I think I've done a better job of
> documenting all of the semantics and corner cases for the encoded I/O
> interface (and if not, I can address this). The other part of the
> problem is that there were various sanity checks in the normal
> read/write paths that were missed or drifted out of sync in the
> ioctls. That requires some vigilance going forward. Maybe starting
> this off as a generic (not Btrfs-specific) ioctl right off the bat
> will help.
>
> If we do go the ioctl route, then we also have to decide how much of
> preadv2/pwritev2 it should emulate. Should it use the fd offset, or
> should that be an ioctl argument? Some of the RWF_ flags would be useful
> for encoded I/O, too (RWF_DSYNC, RWF_SYNC, RWF_APPEND), should it
> support those? These bring us back to Dave's first point.
Oops, I dropped Dave from the Cc list at some point. Adding him back
now.
next prev parent reply other threads:[~2021-06-21 20:55 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 [this message]
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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