On 7 Sep 2003 at 12:32, Daniel Eischen wrote:
> On Sun, 7 Sep 2003, Dan Langille wrote:
>
> > A problem with pthreads and EOT has been identified. See PR 56274. It
> > was suggested the solution was probably just a matter of changing one of
> > the >0 tests to >=0 in uthread_write.c
> >
> > Any comments on that?
>
> I don't know that a return of 0 isn't valid for other devices.
> If this is the case, a return of 0 for blocking writes may break
> other applications.
>
> The patch isn't quite correct (at least looking at -current srcs).
> Lines 98-99 are:
>
> if (blocking && ((n < 0 && (errno == EWOULDBLOCK ||
> errno == EAGAIN)) || (n >= 0 && num < nbytes))) {
>
> This will get entered first if n == 0, and I don't think your
> proposed patch would have any effect. I think you would have
> to change the "n >= 0" above to be "n > 0" in conjunction with
> your patch.
Ahh thank you. That explains why the test results with the original
patch did not differ from -STABLE or 5.1-RELEASE. After adding your
suggestions, we have had success.
The points to note:
1. The status that stopped the writing was 0
2. It wrote 17,256 blocks, and read 17,256 blocks.
Point 1 is key to determining EOT. Point 2 is what you always want
to have...
[EMAIL PROTECTED]:~/tape-test] $ sudo ./tapetest /dev/nsa0
*rewind
Rewound /dev/nsa0
*rawfill
Begin writing blocks of 64512 bytes.
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+++++
weof_dev
Wrote EOF to /dev/nsa0
Write failed. Last block written=17256. stat=0 ERR=Unknown error: 0
*rewind
Rewound /dev/nsa0
*scan
Starting scan at file 0
17256 blocks of 64512 bytes in file 0
End of File mark.
End of File mark.
End of tape
Total files=1, blocks=17256, bytes = 1113219072
*
> This could be solved at the application level by selecting on
> the tape device and performing non-blocking writes to it. Since
> the application knows that a return of 0 is end-of-tape, it
> must also know the difference between talking to a tape device
> and talking to a regular file, socket, etc.
True. But *if* the code is wrong, it should be fixed.
FWIW, the patch follows. As always, opinions and suggestions are
welcome.
--- uthread_write.c.org Sun Sep 7 10:58:31 2003
+++ uthread_write.c Sun Sep 7 15:41:34 2003
@@ -93,7 +93,7 @@
* write:
*/
if (blocking && ((n < 0 && (errno == EWOULDBLOCK ||
- errno == EAGAIN)) || (n >= 0 && num < nbytes))) {
+ errno == EAGAIN)) || (n > 0 && num < nbytes))) {
curthread->data.fd.fd = fd;
_thread_kern_set_timeout(NULL);
@@ -131,7 +131,7 @@
* If there was an error, return partial success
* (if any bytes were written) or else the error:
*/
- } else if (n < 0) {
+ } else if (n <= 0) {
if (num > 0)
ret = num;
else
--
Dan Langille : http://www.langille.org/
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