linux-xfs.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Jason Xing <kerneljasonxing@gmail.com>
To: viro@zeniv.linux.org.uk
Cc: linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: About whether we should support the alignment in the generic_file_splice_read() ?
Date: Fri, 29 Nov 2019 15:50:22 +0800	[thread overview]
Message-ID: <CAL+tcoD8o5A4vgLHHp8dyFV5PmJVL5tu0h-XQavLOiAexmVLRQ@mail.gmail.com> (raw)

Hi all,

Sorry to send this email to you all. I recently noticed there're some
incompatibilities existing in the generic_file_splice_read() function
between 3.X and 4.X kernel. The result will goes wrong if we're using
sendfile() with unaligned offset in 4.X/5.X kernel. But if we do the
same in 3.X kernel, it will surely return success.

Here is the call trace:
1. Using sendfile() with unaligned offset
2. Then it runs into the kernel:
sendfile64()->do_sendfile()->do_splice_direct()->splice_direct_to_actor()->do_splice_to()->splice_read()
3. splice_read() calls the __generic_file_splice_read() in 3.X kernel,
generic_file_splice_read() in 4.X kernel.

In 3.X kernel, this function handles the alignment by using the
PAGE_SHIFT and PAGE_MASK. However, after applying this
commit(82c156f853840645604acd7c2cebcb75ed1b6652) the 4.X no longer
supports the unaligned data.

I'm wondering should we add the alignment process code back again?
Does anyone have idea about why this part got removed? Any information
and suggestions are welcome:-)

Thanks,
Jason

                 reply	other threads:[~2019-11-29  7:51 UTC|newest]

Thread overview: [no followups] expand[flat|nested]  mbox.gz  Atom feed

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=CAL+tcoD8o5A4vgLHHp8dyFV5PmJVL5tu0h-XQavLOiAexmVLRQ@mail.gmail.com \
    --to=kerneljasonxing@gmail.com \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-xfs@vger.kernel.org \
    --cc=viro@zeniv.linux.org.uk \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).