lkml.org 
[lkml]   [2010]   [May]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [PATCH v2 3/4]: sendfile: remove flags paramter of do_splice_direct()
    From
    Date
    [ Removed matthew@wil.cx since I'm getting errors in sending to that address ]


    On Sat, 2010-05-29 at 09:59 +0800, Changli Gao wrote:
    > On Fri, May 28, 2010 at 6:06 PM, Changli Gao <xiaosuo@gmail.com> wrote:
    > > On Fri, May 28, 2010 at 5:40 PM, Miklos Szeredi <miklos@szeredi.hu> wrote:
    > >> On Wed, 26 May 2010, Changli Gao wrote:
    > >>> remove flags paramter of do_splice_direct().
    > >>>
    > >>> the flags parameter of do_splice_direct() doesn't mean non-block read of
    > >>> in file,
    > >>
    > >> Actually, it does. Look at the SPLICE_F_NONBLOCK usage in
    > >> __generic_splice_file_read().
    > >>
    > >
    > > Oh, I checked the code again. You're right. However, why don't we
    > > check the flags of in file instead in __generic_file_splice_read()?
    > >
    >
    > I am afraid that __generic_file_splice_read() should not use SPLICE_F_NONBLOCK.
    >
    > Here is the comment from the commit 42324c62704365d6a3e89138dea55909d2f26afe :
    >
    > <<EOF
    > Linus introduced SPLICE_F_NONBLOCK in commit
    > 29e350944fdc2dfca102500790d8ad6d6ff4f69d
    > (splice: add SPLICE_F_NONBLOCK flag )
    >
    > It doesn't make the splice itself necessarily nonblocking (because the
    > actual file descriptors that are spliced from/to may block unless they
    > have the O_NONBLOCK flag set), but it makes the splice pipe operations
    > nonblocking.
    >
    > Linus intention was clear : let SPLICE_F_NONBLOCK control the splice
    > pipe mode only
    > EOF
    >
    > And I have greped the whole code:
    >


    > kernel/trace/trace.c: if (flags & SPLICE_F_NONBLOCK)
    >
    > besides the __generic_file_splice_read(), there are two users: relay
    > and trace. I believe they all misuse this flag.
    >


    The trace splice never blocks anyway. Since we have no good method to
    wake up a waiter. That is, we never know if it is safe to call wakeup,
    because a tracepoint may be in a section where the rq lock is held.

    The only thing that passing SPLICE_F_NONBLOCK does in that code is to
    return -EAGAIN when there is nothing in the buffer. Otherwise, it
    returns 0.

    -- Steve





    \
     
     \ /
      Last update: 2010-05-29 18:23    [W:0.023 / U:90.284 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site