: sendfile: remove flags paramter of do_splice_direct()
in [Kernel]
|
Prev: [PATCHv2 2/7] USB: gadget: f_mass_storage: fsg_add() renamed to fsg_bind_config()
Next: [PATCHv2 1/7] USB: gadget: g_mass_storage: static data instead of dynamic allocation
From: Changli Gao on 28 May 2010 06:10 On Fri, May 28, 2010 at 5:40 PM, Miklos Szeredi <miklos(a)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()? -- Regards， Changli Gao(xiaosuo(a)gmail.com) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Changli Gao on 28 May 2010 22:00 On Fri, May 28, 2010 at 6:06 PM, Changli Gao <xiaosuo(a)gmail.com> wrote: > On Fri, May 28, 2010 at 5:40 PM, Miklos Szeredi <miklos(a)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: fs/splice.c: if (spd->flags & SPLICE_F_NONBLOCK) { fs/splice.c: if (flags & SPLICE_F_NONBLOCK) { fs/splice.c: if (sd->flags & SPLICE_F_NONBLOCK) fs/splice.c: if (flags & SPLICE_F_NONBLOCK) { fs/splice.c: if (flags & SPLICE_F_NONBLOCK) { fs/splice.c: if (flags & SPLICE_F_NONBLOCK) { fs/splice.c: if (!ret && ipipe->waiting_writers && (flags & SPLICE_F_NONBLOCK)) fs/splice.c: * applicable one is SPLICE_F_NONBLOCK. include/linux/splice.h:#define SPLICE_F_NONBLOCK (0x02) /* don't block on the pipe splicing (but */ kernel/relay.c: if (flags & SPLICE_F_NONBLOCK) 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. -- Regards， Changli Gao(xiaosuo(a)gmail.com) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Changli Gao on 29 May 2010 20:00 On Sun, May 30, 2010 at 12:20 AM, Steven Rostedt <rostedt(a)goodmis.org> wrote: > [ Removed matthew(a)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(a)gmail.com> wrote: >> > On Fri, May 28, 2010 at 5:40 PM, Miklos Szeredi <miklos(a)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. > But why not use (file->f_flags & O_NONBLOCK) instead, as tracing_splice_read_pipe() does? -- Regards， Changli Gao(xiaosuo(a)gmail.com) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Changli Gao on 29 May 2010 23:30
On Sun, May 30, 2010 at 8:39 AM, Steven Rostedt <rostedt(a)goodmis.org> wrote: > Probably because I copied the code from something that used > SPLICE_F_NONBLOCK ;-) > From the relay API implementation? > But userspace passes that flag too. Although, maybe I just don't > understand the API fully. > this flag is a little confusing. It is much like: flags = fcntl(pipe_fd, F_GETFL); fcntl(pipe_fd, F_SETFL, flags | O_NONBLOCK); splice(..pipe_fd..., 0); // without O_NONBLOCK fcntl(pipe_fd, F_SETFL, falgs); In fact, setting O_NONBLOCK is the only way of letting splice pipe operations non-blockable currently. When splicing, splice doesn't refer to the pipe file's f_flags. :( -- Regards， Changli Gao(xiaosuo(a)gmail.com) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |