Re: [9fans] devsd & media changed errors

when a disk or a cdrom reports that it has 0 sectors
devsd won't let you write to the control file. it gives

this is not true. what is true is that if you open
the ctl file and then the media changes, then you
are required to reopen the ctl file in order to start
using it. this is true of all the disk files.

russ, you are not correct. i just retried using the pc/sdata
driver.

first, if you have a blank cdrom in the tray, you can't

echo dma on>/dev/sdXX/ctl
i can't test this, but i don't believe this is true.
(see above.)

this is cut-n-paste from just now. i ejected a blank disk and reinserted it.

ladd# cat ctl
inquiry TSSTcorpCD/DVDW SH-S182MSB00 0726 0137PL
config 85C0 capabilities 0F00 dma 00550004 dmactl 00000000
ladd# echo dma on>ctl
echo: write error: media or partition has changed
ladd# echo dma on>ctl
echo: write error: media or partition has changed

scuzz is able to identify, though.

worse, if i have a drive that sometimes needs to be reset
manually. (some sata drives have loopy firmware.) i can't

echo reset>/dev/sdE5/ctl

to fix it.

i *know* this isn't true. i do this all the time (personally i think
the sdmv driver is not quite driving the disks right).

i wasn't using the sdmv50xx driver. i have had similar results with
the sdata driver and a new driver that i'm working on.

since ctl is used for things like partitioning the disk, i think
it is reasonable that if the disk has changed since you
opened the file, then you should need to reopen it.

this sounds reasonable to me.

i do find it annoying that when i reset a disk this way,
it appears to the sd framework as if the underlying
disk has changed, so all the partitions go away, and
all the open file descriptors get poisoned, but i'm not
sure this is incorrect behavior. the media did sort of
change -- it went away and came back.

i consider this a driver problem. in the ahci driver i'm currently
working on, if "new" drive has the same serial# as the old drive,
i don't report a media change.

admittedly, this is a huristic becaus you could have removed the
drive, paved it and put it back. but that might fall under the
"deserves to loose" banner. in any event, the drive can't ever
say with confidence that all the data is the same as was written.

- erik
.

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