On Sun, May 30, 2010 at 12:20 AM, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > [ 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. > But why not use (file->f_flags & O_NONBLOCK) instead, as tracing_splice_read_pipe() does? -- Regards， Changli Gao(xiaosuo@xxxxxxxxx) -- 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
