RE: Encountered a Null Pointer Problem on the SCSI Layer

From: Peter Wong (wpeter@us.ibm.com)
Date: Tue Jan 29 2002 - 10:03:42 EST


Jesper,

     Let's use sd_find_queue() as an example.

     If the array pointed by rscsi_disk has been allocated,
dpnt cannot be null.

     If rscsi_disk has not been allocated, dpnt = &rscsi_disks[target]
may not be null depending on the value of target. Thus, "if (!dpnt)"
is not sufficient anyway.

     You can also look at sd_attach(), in which "if (!dpnt->device)" is
tested, not "if (!dpnt)".

Regards,
Peter

Wai Yee Peter Wong
IBM Linux Technology Center, Performance Analysis
email: wpeter@us.ibm.com

                                                                                                                                       
                      Jesper Juhl
                      <jju@dif.dk> To: "'Pete Zaitcev '" <zaitcev@redhat.com>, Peter Wong/Austin/IBM@IBMUS,
                                                "'linux-kernel@vger.kernel.org '" <linux-kernel@vger.kernel.org>
                      01/28/02 05:57 PM cc: "'Jens Axboe '" <axboe@suse.de>
                                               Subject: RE: Encountered a Null Pointer Problem on the SCSI Layer
                                                                                                                                       
                                                                                                                                       
                                                                                                                                       

> - if (!dpnt)
> + if (!dpnt->device)
> return NULL; /* No such device */

Maybe I don't understand this right, but shouldn't that be

if (!dpnt || !dpnt->device)
        return NULL; /* No such device */

?

Best regards,
Jesper Juhl
jju@dif.dk

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