Re: Concurrent SG_SCSI_RESET ioctls

[Douglas Gilbert <dgilbert@interlog.com>]

On 14-10-24 04:51 PM, Christoph Hellwig wrote:
> On Tue, Oct 14, 2014 at 12:42:26PM -0400, Douglas Gilbert wrote:
>> I don't mind if you change it. However I plan to release
>> sg3_utils-1.40 in the next 2 or 3 weeks, so that would
>> be the earliest a revised sg_reset would be available for
>> distros. Improving error reports is something I always
>> like to do (so ENODEV for the "in progress" case seems a
>> bit strident).
>
> Doug, are you fine with changing the error code to EAGAIN
> similar to what we get elsewhere when a O_NONBLOCK open
> would have to block?  If that's something you can prepare
> sg3_utils for I'd like to send a patch for it for the 3.19 merge
> window.

Yes, that's fine.

Just expanded the sg_reset ioctl erorr processing to this:

     switch (errno) {
     case EBUSY:
         fprintf(stderr, ME "BUSY, may be resetting now\n");
         break;
     case ENODEV:
         fprintf(stderr, ME "'no device' error, may be temporary while "
                 "device is resetting\n");
         break;
     case EAGAIN:
         fprintf(stderr, ME "try again later, may be resetting now\n");
         break;
     case EIO:
         fprintf(stderr, ME "reset (for value=0x%x) may not be "
                 "available\n", k);
         break;
     case EPERM:
     case EACCES:
         fprintf(stderr, ME "reset requires CAP_SYS_ADMIN (root) "
                 "permission\n");
         break;
     case EINVAL:
         fprintf(stderr, ME "SG_SCSI_RESET not supported (for "
                 "value=0x%x)\n", k);
     default:
         perror(ME "SG_SCSI_RESET failed");
         break;
     }

The ENODEV, EAGAIN and EPERM entries are new. In the sg_reset
implementation currently in the field they will drop down to
the default case and do a perror().

With the ioctl(SG_IO), it is sufficient to give a user permissions
on the device node (e.g. 'chmod 666 /dev/sg2; sg_turs /dev/sg2')
to pass through a command. However with ioctl(SG_SCSI_RESET),
another check is done by the ioctl and if it fails then it yields
EACCES .


Doug Gilbert