[PATCH] : libc_r/uthread/uthread_write.c

[Dan Langille]

Daniel:  It appears the patch which was comitted didn't include 
everything it should.  I blame myself because the patch below 
contains both debugging code and is reversed.   I will submit a PR 
with a patch.  In brief, what is missing is:

+                               if (n == 0) {
+                                       break;
+                               }
+

Oops.


On 17 Sep 2003 at 10:32, Dan Langille wrote:

> On 16 Sep 2003 at 20:49, Daniel Eischen wrote:
> 
> > On Tue, 16 Sep 2003, Dan Langille wrote:
> > 
> > > I've had preliminary success with this patch.  More testing needs
> > > to be done, but in the meantime, I would appreciate reviews and
> > > comments.  The patched code is available from
> > > http://beta.freebsddiary.org/tmp/uthread_write.c and the patch
> > > appears below.
> > > 
> > > In short, the logic has been changed to ensure that if __sys_write
> > > returns zero, this value is returned by _write.
> > 
> > I think this is not quite correct.  Since libc_r is looping
> > and some data may have been read, then the partial byte count
> > should be returned, not zero.  It is possible the partial byte
> > count could also be zero in some cases, so it would result
> > in zero being returned in those instances.
> 
> I see what you mean. Please have a look at 
> http://beta.freebsddiary.org/tmp/uthread_write.c2
> The patch appears at the end of this message.
> 
> This version will return the partial byte count (which has always been
> zero in testing) but exit the loop if the return code is zero.
> 
> > I think the problem lies with the SCSI tape device. It should
> > either return 0 or -1 with errno=ENOSPC on a write that detects an
> > EOT, not partial byte count.
> 
> You are referring to sa(4)?
> 
> > If you are using libkse or
> > libthr, you will get a partial byte count and not zero because
> > the tape driver returns the (partial) bytes written.  So exiting the
> > loop in libc_r and returning 0 would only seem to correct the
> > "problem" for libc_r.
> 
> The problem  found when running under pthreads on 4.8-stable [i.e. EOT
> is not returned to the application code] is not found with libkse on
> 5.1-current.
> 
> --- uthread_write.c	Wed Sep 17 06:23:43 2003
> +++ uthread_write.c.org	Tue Sep 16 12:14:22 2003
> @@ -39,7 +39,6 @@
>  #include <unistd.h>
>  #include <pthread.h>
>  #include "pthread_private.h"
> -#include <syslog.h>
> 
>  ssize_t
>  _write(int fd, const void *buf, size_t nbytes)
> @@ -71,10 +70,6 @@
>    /* Check if file operations are to block */
>    blocking = ((_thread_fd_getflags(fd) & O_NONBLOCK) == 0);
> 
> -		setlogmask (LOG_UPTO (LOG_NOTICE));
> -		openlog("uthread_write.c", LOG_CONS | LOG_PID | LOG_NDELAY, 
> LOG_LOCAL1);
> -		syslog (LOG_NOTICE, "uthread_write.c : blocking = '%d'", 
> blocking);
> -
>    /*
>     * Loop while no error occurs and until the expected number
>     * of bytes are written if performing a blocking write:
> @@ -98,7 +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);
> 
> @@ -136,16 +131,11 @@
>      * 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
>       ret = n;
> -
> -				if (n == 0) {
> -					syslog (LOG_NOTICE, "zero has been returned in uthread_write.c;
> num = '%d'", num); -					break; -				}
> 
>     /* Check if the write has completed: */
>     } else if (num >= nbytes)
> 
> -- 
> Dan Langille : http://www.langille.org/
> 
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-- 
Dan Langille : http://www.langille.org/