From: Al Viro <viro@zeniv.linux.org.uk>
To: Omar Sandoval <osandov@osandov.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Dave Chinner <david@fromorbit.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>,
Dave Chinner <dchinner@redhat.com>
Subject: Re: [PATCH RESEND x3 v9 1/9] iov_iter: add copy_struct_from_iter()
Date: Wed, 23 Jun 2021 22:26:23 +0000 [thread overview]
Message-ID: <YNO1D++slcnNoLVU@zeniv-ca.linux.org.uk> (raw)
In-Reply-To: <YNOuiMfRO51kLcOE@relinquished.localdomain>
On Wed, Jun 23, 2021 at 02:58:32PM -0700, Omar Sandoval wrote:
> Ah, I was stuck on thinking about this calling convention:
>
> struct encoded_iov encoded_iov;
> char compressed_data[...];
> struct iovec iov[] = {
> { &encoded_iov, sizeof(encoded_iov) },
> { compressed_data, sizeof(compressed_data) },
> };
> preadv2(fd, iov, 2, -1, RWF_ENCODED);
>
> But what you described would look more like:
>
> // Needs to be large enough for maximum returned header + data.
> char buffer[...];
> struct iovec iov[] = {
> { buffer, sizeof(buffer) },
> };
> preadv2(fd, iov, 2, -1, RWF_ENCODED);
> // We should probably align the buffer.
> struct encoded_iov *encoded_iov = (void *)buffer;
> char *data = buffer + encoded_iov->size;
>
> That's a little uglier, but it should work, and allows for arbitrary
> extensions. So, among these three alternatives (fixed size structure
> with reserved space, variable size structure like above, or ioctl),
> which would you prefer?
Variable-sized structure would seem to be the easiest from the kernel
POV and the interface is the easiest to describe - "you read the
encoded data preceded by the header"...
next prev parent reply other threads:[~2021-06-23 22:26 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 [this message]
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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