[cups.bugs] [LOW] STR #2664: usb backend busy-loops due to runloop logic error

[twaugh.redhat]

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[STR New]

A logic error in backend/runloop.c causes the usb backend to use very much
more power than it needs to.

The situation that triggers this is that backendRunLoop() is entered with
use_bc==0 and side_cb!=NULL.

When print_bytes==0 in this situation, I think that this piece of code:

     if (print_bytes || !use_bc)
       FD_SET(device_fd, &output);

is trying to add device_fd to the output set if the select() call will be
skipped.  This worked up until revision 6170, which added the side_cb
parts.

A patch to fix the logic error is attached.  Original bug report:
  https://bugzilla.redhat.com/show_bug.cgi?id=426653

Link: http://www.cups.org/str.php?L2664
Version: 1.3.5
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