GEOM weirdness with SD flash reader?
Nikolay Pavlov
quetzal at zone3000.net
Mon Jul 2 11:13:50 UTC 2007
On Sunday, 1 July 2007 at 22:19:11 -0600, M. Warner Losh wrote:
> In message: <4688791D.6050007 at root.org>
> Nate Lawson <nate at root.org> writes:
> : M. Warner Losh wrote:
> : > In message: <46880F1C.3020602 at root.org>
> : > Nate Lawson <nate at root.org> writes:
> : > : Yes, you're exactly right. However, shouldn't a read from a device
> : > : trigger a re-taste if the media is removable?
> : >
> : > I don't think it does. The driver is expected to poll, however...
> : >
> : > : So the fdisk of da2
> : > : should have caused it to re-read the MBR and create /dev/da2s1. I think
> : > : maybe there should be a flag set for devices with removable media that
> : > : causes the device to be re-tasted on every mount request.
> : >
> : > Is there even a removable flag to disks?
> :
> : In SCSI there is, removable flag combined with medium not present:
> :
> : da2 at umass-sim1 bus 1 target 0 lun 2
> : da2: <Generic STORAGE DEVICE 0001> Removable Direct Access SCSI-0 device
> : ^^^^^^^^^
> : da2: 40.000MB/s transfers
> : da2: Attempt to query device size failed: NOT READY, Medium not present
>
> I think you've misunderstood my point. I know that SCSI has this
> flag, but I can't find anything in GEOM that it would map to. It
> seems a common enough situation that having such a flag in GEOM would
> be beneficial and easy to implement.
>
> : What if we kicked off a thread to run every 3 seconds that did a quick
> : poll of such devices and sent a devd notify if they arrived (i.e. medium
> : present)? It wouldn't work for floppy drives, but we could make this
> : part of the da driver or something in usermode like devd itself calling
> : camcontrol?
>
> In the past, people have said that polling messes up multimedia
> access, so it hasn't happened.
>
> But wouldn't a simple daemon in userland do the same thing? Or
> parsing the output of camcontrol inquiry? Camcontrol rescan is a nop
> for these devices.
Hald is using the same tactic. My dmesg is full of poll messages when i
am using cardreader with it.
--
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- Best regards, Nikolay Pavlov. <<<-----------------------------------
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