misc/144696: tcdrain(3) does not work right with uart(4) driver

Uniballer nobody at igetenoughspamthanku.org
Fri Mar 12 15:20:02 UTC 2010

>Number:         144696
>Category:       misc
>Synopsis:       tcdrain(3) does not work right with uart(4) driver
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    freebsd-bugs
>State:          open
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Fri Mar 12 15:20:01 UTC 2010
>Originator:     Uniballer
>Release:        8.0-RELEASE-p2
FreeBSD ????.xxxx.com 8.0-RELEASE-p2 FreeBSD 8.0-RELEASE-p2 #0: Tue Jan  5 16:02:27 UTC 2010     root at i386-builder.daemonology.net:/usr/obj/usr/src/sys/GENERIC  i386

tcdrain(3) does not wait for serial output to complete when used with the uart(4) driver.  This worked correctly on 6.4 and 7.x with the sio(4) driver.

Loop back a serial port, write a long buffer to it, then call tcdrain(3) to wait for output to complete, and call tcflush(3) to get rid of the data.  A subsequent read will show that part of the data is in the receive buffer, probably because it was received after tcflush(3) was called because tcdrain(3) was called early.

See http://forums.freebsd.org/showthread.php?t=12154 for more info and sample code.



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