Re: Need help tracing regular write activity in 5 s interval

[Padraig Brady <padraig@antefacto.com>]

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Padraig Brady wrote:
> Owen Taylor wrote:
> 
>> Padraig Brady <padraig@antefacto.com> writes:
>>
>>> I'm sure it will :-)
>>>
>>> However this it just masking the "problem"
>>
>>
>> Well, the question is, "what is the problem"?
>> Your problem is that a debug message is being output by the kernel and
>> filling your logs. If the debug message doesn't do anybody any good
>> (and it doesn't) then removing the debug message is a fine way of
>> solving the problem.
> 
> 
> True. But I thought there might be (future) side affects of
> cdrom_media_changed() always returning true. Why is it there at all?

I had a quick look at this and basically cdrom_media_changed()
is only valid when there is a disc in the drive. If the drive
is open or empty then it always returns true. There are a couple
of comments saying it's like this to catch buggy drives, but
hence the interface is broken IMHO and should be removed/fixed?

The attached test program illustrates the problem.

Padraig.


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#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <linux/ioctl.h>
#include <linux/cdrom.h>

/* drives have capabilities (CDC*) like CDC_MEDIA_CHANGED.
   These done with CDROM_SET_OPTIONS ioctl. perhaps magicdev
   should turn this off as it doesn't use anyway? */

int main(void) {
    int cd = open("/dev/cdrom", O_RDONLY|O_NONBLOCK); /* This causes VFS: disk change ... */
    while(1) {
        //int cd = open("/dev/cdrom", O_RDONLY|O_NONBLOCK);
        printf ("media changed[%d]\n", ioctl(cd, CDROM_MEDIA_CHANGED, CDSL_CURRENT));
        /*
        switch (ioctl(cd, CDROM_DRIVE_STATUS, CDSL_CURRENT)) {
            case CDS_DISC_OK: printf("DISK_OK\n"); break;
            case CDS_TRAY_OPEN: printf("TRAY_OPEN\n"); break;
            case CDS_DRIVE_NOT_READY: printf("DRIVE_NOT_READY\n"); break;
            default: printf("default\n"); break;
        }
        */
        //close(cd);
        sleep(2);
    }
}