[ Removed matthew@xxxxxx 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@xxxxxxxxx> wrote: > > On Fri, May 28, 2010 at 5:40 PM, Miklos Szeredi <miklos@xxxxxxxxxx> 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 -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
