On Sat, Dec 11, 2010 at 08:35:00PM +0000, Jacob Meuser wrote:
> On Sat, Dec 11, 2010 at 08:14:24PM +0100, Mark Kettenis wrote:
> > > Date: Wed, 8 Dec 2010 06:07:30 +0000
> > > From: Jacob Meuser <jake...@sdf.lonestar.org>
> > >
> > > I recently got a hp officejet 4500. it's a 3-in-1 printer/scanner/fax.
> > > printing works great with the hplip packages. scanning doesn't work at
> > > all.
> > >
> > > I tracked the problem to read() failing in usb_bulk_read() in libusb.
> > > errno was EINTR. so I made this function just continue when read() got
> > > EINTR. I could then scan, but not very reliably.
> > >
> > > so I went into the kernel, and tracked it to usbdi_util.c:
> > >
> > > @ usbd_bulk_transfer(usbd_xfer_handle xfer, usbd_pipe_ha
> > >
> > > error = tsleep((caddr_t)xfer, PZERO | PCATCH, lbl, 0);
> > > splx(s);
> > > if (error) {
> > > DPRINTF(("usbd_bulk_transfer: tsleep=%d\n", error));
> > > usbd_abort_pipe(pipe);
> > > return (USBD_INTERRUPTED);
> > > }
> > >
> > > on a hunch, I changed 'PZERO | PCATCH' to 'PWAIT'. then scanning became
> > > 100% reliable. even full-page 1200dpi (~525MB of data) worked
> > > perfectly.
> > >
> > > great. but, what if we need to interrupt the transfer. we don't want
> > > to hang here.
> > >
> > > well, this function takes a timeout. so, it's possible to make it
> > > return, even if the transfer stalls. but is this used? I looked
> > > at the ports that use libusb. setting 0/infinite timeout for bulk
> > > transfers is extremely rare, only set in code marked experimental
> > > or problematic. in the kernel, there are however some callers that
> > > use USBD_NO_TIMEOUT.
> > >
> > > so, I offer the following. if there's no timeout, behave like we do
> > > now and catch signals, and if there's a timeout, ignore signals.
> > >
> > > I did the same for interrupt transfers because the situation seems
> > > to be the same.
> > >
> > > thoughts?
> >
> > Sorry, but this very much feels like you're hacking around a bug in
> > the application you're using. If it installs signal handler without
> > specifying the SA_RESTART flag, it has to deal with read(2) failing
> > with EINTR.
>
> that application would be libusb itself. is a library supposed
> to be messing with signals?
to be clear, the actual read() is in usb_bulk_read() in libusb.
so, the application doesn't really know that there's a read().
I tried making libusb continue, but the problem is that when
usbd_bulk_transfer catches the signal, it aborts everything in
the pipe. restarting from there correctly is complicated,
probably not even possible in a sane way.
>
>
> > > Index: usbdi_util.c
> > > ===================================================================
> > > RCS file: /cvs/src/sys/dev/usb/usbdi_util.c,v
> > > retrieving revision 1.25
> > > diff -u -p usbdi_util.c
> > > --- usbdi_util.c 26 Jun 2008 05:42:19 -0000 1.25
> > > +++ usbdi_util.c 8 Dec 2010 04:58:49 -0000
> > > @@ -426,7 +426,7 @@ usbd_bulk_transfer(usbd_xfer_handle xfer, usbd_pipe_ha
> > > u_int16_t flags, u_int32_t timeout, void *buf, u_int32_t *size, char
> > > *lbl)
> > > {
> > > usbd_status err;
> > > - int s, error;
> > > + int s, error, pri;
> > >
> > > usbd_setup_xfer(xfer, pipe, 0, buf, *size, flags, timeout,
> > > usbd_bulk_transfer_cb);
> > > @@ -437,7 +437,8 @@ usbd_bulk_transfer(usbd_xfer_handle xfer, usbd_pipe_ha
> > > splx(s);
> > > return (err);
> > > }
> > > - error = tsleep((caddr_t)xfer, PZERO | PCATCH, lbl, 0);
> > > + pri = timeout == USBD_NO_TIMEOUT ? (PZERO | PCATCH) : PWAIT;
> > > + error = tsleep((caddr_t)xfer, pri, lbl, 0);
> > > splx(s);
> > > if (error) {
> > > DPRINTF(("usbd_bulk_transfer: tsleep=%d\n", error));
> > > @@ -467,7 +468,7 @@ usbd_intr_transfer(usbd_xfer_handle xfer, usbd_pipe_ha
> > > u_int16_t flags, u_int32_t timeout, void *buf, u_int32_t *size, char
> > > *lbl)
> > > {
> > > usbd_status err;
> > > - int s, error;
> > > + int s, error, pri;
> > >
> > > usbd_setup_xfer(xfer, pipe, 0, buf, *size, flags, timeout,
> > > usbd_intr_transfer_cb);
> > > @@ -478,7 +479,8 @@ usbd_intr_transfer(usbd_xfer_handle xfer, usbd_pipe_ha
> > > splx(s);
> > > return (err);
> > > }
> > > - error = tsleep(xfer, PZERO | PCATCH, lbl, 0);
> > > + pri = timeout == USBD_NO_TIMEOUT ? (PZERO | PCATCH) : PWAIT;
> > > + error = tsleep(xfer, pri, lbl, 0);
> > > splx(s);
> > > if (error) {
> > > DPRINTF(("usbd_intr_transfer: tsleep=%d\n", error));
>
> --
> jake...@sdf.lonestar.org
> SDF Public Access UNIX System - http://sdf.lonestar.org
--
jake...@sdf.lonestar.org
SDF Public Access UNIX System - http://sdf.lonestar.org
