linux-kernel - Re: [PATCH] fs: io_uring.c: Add skip option for __io_sqe_files

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Date:   Tue, 26 Jan 2021 12:14:21 -0500
From:   Noah Goldstein <goldstein.w.n@...il.com>
To:     Pavel Begunkov <asml.silence@...il.com>
Cc:     noah <goldstein.n@...tl.edu>, Jens Axboe <axboe@...nel.dk>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        "open list:IO_URING" <io-uring@...r.kernel.org>,
        "open list:FILESYSTEMS (VFS and infrastructure)" 
        <linux-fsdevel@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] fs: io_uring.c: Add skip option for __io_sqe_files_update

On Tue, Jan 26, 2021 at 7:29 AM Pavel Begunkov <asml.silence@...il.com> wrote:
>
> On 22/12/2020 02:10, Noah Goldstein wrote:
> > On Sun, Dec 20, 2020 at 03:18:05PM +0000, Pavel Begunkov wrote:
> >> On 20/12/2020 06:50, noah wrote:> From: noah <goldstein.n@...tl.edu>
> >>>
> >>> This patch makes it so that specify a file descriptor value of -2 will
> >>> skip updating the corresponding fixed file index.
> >>>
> >>> This will allow for users to reduce the number of syscalls necessary
> >>> to update a sparse file range when using the fixed file option.
> >>
> >> Answering the github thread -- it's indeed a simple change, I had it the
> >> same day you posted the issue. See below it's a bit cleaner. However, I
> >> want to first review "io_uring: buffer registration enhancements", and
> >> if it's good, for easier merging/etc I'd rather prefer to let it go
> >> first (even if partially).
>
> Noah, want to give it a try? I've just sent a prep patch, with it you
> can implement it cleaner with one continue.
>

 Absolutely. Will get on it ASAP.

> >>
> >> diff --git a/fs/io_uring.c b/fs/io_uring.c
> >> index 941fe9b64fd9..b3ae9d5da17e 100644
> >> --- a/fs/io_uring.c
> >> +++ b/fs/io_uring.c
> >> @@ -7847,9 +7847,8 @@ static int __io_sqe_files_update(struct io_ring_ctx *ctx,
> >>      if (IS_ERR(ref_node))
> >>              return PTR_ERR(ref_node);
> >>
> >> -    done = 0;
> >>      fds = u64_to_user_ptr(up->fds);
> >> -    while (nr_args) {
> >> +    for (done = 0; done < nr_args; done++) {
> >>              struct fixed_file_table *table;
> >>              unsigned index;
> >>
> >> @@ -7858,7 +7857,10 @@ static int __io_sqe_files_update(struct io_ring_ctx *ctx,
> >>                      err = -EFAULT;
> >>                      break;
> >>              }
> >> -            i = array_index_nospec(up->offset, ctx->nr_user_files);
> >> +            if (fd == IORING_REGISTER_FILES_SKIP)
> >> +                    continue;
> >> +
> >> +            i = array_index_nospec(up->offset + done, ctx->nr_user_files);
> >>              table = &ctx->file_data->table[i >> IORING_FILE_TABLE_SHIFT];
> >>              index = i & IORING_FILE_TABLE_MASK;
> >>              if (table->files[index]) {
> >> @@ -7896,9 +7898,6 @@ static int __io_sqe_files_update(struct io_ring_ctx *ctx,
> >>                              break;
> >>                      }
> >>              }
> >> -            nr_args--;
> >> -            done++;
> >> -            up->offset++;
> >>      }
> >>
> >>      if (needs_switch) {
>
> --
> Pavel Begunkov