Bug 4563 - read from usblp don't work
Summary: read from usblp don't work
Alias: None
Product: Drivers
Classification: Unclassified
Component: USB (show other bugs)
Hardware: i386 Linux
: P2 high
Assignee: Greg Kroah-Hartman
Depends on:
Blocks: USB
  Show dependency tree
Reported: 2005-04-30 01:33 UTC by Jean-Jacques Sarton
Modified: 2005-08-19 09:18 UTC (History)
1 user (show)

See Also:
Kernel Version: 2.6.9 2.6.10 2.6.11
Tree: Mainline
Regression: ---


Description Jean-Jacques Sarton 2005-04-30 01:33:50 UTC
Distribution:           Fedora Core 3
Hardware Environment:   EPSON Printer on Notebook
Software Environment:   Kernel 2.6.9, 2.6.10. 2.6.11, readin of Printer
                        informations via the status monitor mtink.
Problem Description:    The read() call is no more blockink as for older kernel.
                        Furthermore read may return characters which are not
                        send bay the printer.
                        The poll call don't block for the POLLIN event query.

Steps to reproduce:     cat /dev/usb/lp0 is suffincientz in order to see that 
                        the read call is not blocking. Attaching an EPSON 
                        printer via USB and querying datas fail
                        (http;// xwtools.automatix.de)
Comment 1 Greg Kroah-Hartman 2005-06-01 14:45:23 UTC
What kernel did the read() call block for you?
We need more information here.  Does the driver not work properly?
Comment 2 Jean-Jacques Sarton 2005-06-02 09:19:10 UTC
I try to read data fronn the printer and I expect that if the
printer have nothing to send to my application, the read call

On the 2.4 kernel serie the call was blocking, this is no more
the the fact with the 2.6 kernels.

In my opinion the driver dont work properl. If an application issue
an open("/dev/usb/lp0", O_RDWR); as consecutive read has to block
unless an appropriate system call make the read call non blocking.

What for data do you need ? 
Comment 3 Greg Kroah-Hartman 2005-08-18 13:51:24 UTC
Sorry, but that's not the way the driver works anymore.

Not much I can do about it...
Comment 4 Jean-Jacques Sarton 2005-08-19 08:40:21 UTC
Therefore the parallel printer port and the  usb printer port will
work differently, this is not a nice feature.
Comment 5 Greg Kroah-Hartman 2005-08-19 09:09:18 UTC
Ok, I just tested this with my printer, and 2.6.13-rc6, and it blocks if no
data is to be read from the printer.  So yes, it does work like 2.4 this way.

Perhaps your printer really is responding with data?

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