Date: Fri, 14 Nov 2003 10:08:08 -0500 From: "Dan Langille" <dan@langille.org> To: Daniel Eischen <eischen@vigrid.com> Cc: hackers@freebsd.org Subject: Re: [PATCH] : libc_r/uthread/uthread_write.c Message-ID: <3FB4A988.15769.9BCCC68@localhost> In-Reply-To: <3F683824.14446.AB8FEDA@localhost> References: <Pine.GSO.4.10.10309162041380.28900-100000@pcnet5.pcnet.com>
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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/
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