On Monday 10 December 2018 15:02:44 Thomas Schmitt wrote: > Hi, > > Gene Heskett wrote: > > Perhaps that patch could be reverted, > > It had its legitimate intentions, 10 years ago. > See > > > https://github.com/torvalds/linux/commit/210ba1d1724f5c4ed87a2ab1a21ca >861a915f734 > > and a glimpse of the following woes > http://lkml.iu.edu/hypermail//linux/kernel/0807.0/0287.html > (The culprits already suffered duely. Hehehe.)
And rather than fix it, walked away. > > The decisive change is not easy to spot. It's the loss of the function > > static int test_unit_ready(Scsi_CD *cd) > > with the line > > return sr_do_ioctl(cd, &cgc); > > sr_do_ioctl() has a waiting loop that eats "still undecided" replies > and retries at most 10 times. It still exists in the current kernel > > > https://github.com/torvalds/linux/blob/master/drivers/scsi/sr_ioctl.c > > where in line 223 ff. we can see the old timeout of 20 seconds > > if (!cgc->quiet) > sr_printk(KERN_INFO, cd, > "CDROM not ready yet.\n"); > if (retries++ < 10) { > /* sleep 2 sec and try again */ > ssleep(2); > goto retry; > } else { > /* 20 secs are enough? */ > err = -ENOMEDIUM; > break; > } > > The replacement for test_unit_ready() is a call to > scsi_test_unit_ready() which does not call a function with retry loop. > > For the purpose of sr_drive_status(), the loop is really > inappropriate. This function shall obtain the drive status and not > wait until the status of the medium is decided. > > Regrettably the subsequent correction attempts never reached the > doings of drivers/cdrom/cdrom.c function open_for_data(). By the > original change it lost its loop and never got a new one. > > My fix proposal is to create a function with such a loop and to let > open_for_data() use it instead of the call of cdo->drive_status(), > which actually is sr_drive_status(). > Currently this call is in line 1068 of > > https://github.com/torvalds/linux/blob/master/drivers/cdrom/cdrom.c > > > and the timeout made say 2 minutes, > > by which time the drive should be able to make up its mind > > 30 seconds seems to be enough for all normal situations. My longest > experiment result with various drives and media was 18 seconds. > One would have to convince the hypothetical committer why 120 is > needed. > I expect you have a better understanding than I do. What I will say is if you fix it, there will be flowery words written by several, and a hand cooler offered if you show up at my place thirsty. > But before commit comes the test and before test comes the recent > kernel on real iron. I only have code for now and feel fewly talented > for the missing steps. > > > That I think we can all agree is a PITA. > > Oh. I know some more such dumplings. > So do I, Thomas, but this is supposedly a polite list. :) > > Have a nice day :) > > Thomas -- Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene>
