On Fri, 15 Jan 2010, Kay Sievers wrote:
>
> blkid is udev's native tool, and we need to use it. But we need to
> optimize its use with devices like this, I guess. It's similar to
> plain old floppy drives which do not behave well when tried to read
> all sort of signatures at random places. :)
Well, to be fair, neither do some USB devices. Lots of them lock up if you
probe them beyond the end, which is why the kernel has various fixups to
make sure that the size is right etc.
> The devkit-disks-part-id thing is part of DeviceKit-disks, the HAL
> successor, and does only parse the partiton table in the first blocks
> of the volume, and nothing else. This tool will entirely go away and
> be replaced by the (now existing) partition table parsing code in
> blkid.
Ok. So the only thing worth looking at is blkid.
> > - What am I supposed to do with a disk that has no UUID? It doesn't get
> > mounted by hald at all.
>
> On GNOME, it should be Nautilus which requests the mount from the
> DeviceKit-disks service. HAL is not used anymore, and is expected not
> to be needed in future distro releases like Fedora 13.
>
> Nothing should depend on a UUID found on the volume to trigger
> automounting. The stuff you've shown earlier:
> $ blkid -o udev -p /dev/sdc1
> ID_FS_TYPE=vfat
> ID_FS_USAGE=filesystem
> should be enough to make automounting work.
Hmm. So it might be the odd timing pattern after all, and maybe udev ends
up announcing the device too early or something. And it ends up being
noticeable only when the disk is _so_ slow that even reading some minor
data off it takes half a second.
Is there some way to get a trace of what these tools do to figure out what
goes wrong?
> > And no, I can't just add a UUID to the thing. It's a piece of external
> > hardware with odd firmware that I don't control.
>
> Yeah, seems odd, that this does not work, event when it would take a
> minute. Does it show up in Nautilus, so that you can click on an icon
> to mount it, or does it not show up at all?
It does not show up at all. And I have no idea why, because the whole
udev->DeviceKit thing is pretty invisible to me (see above on the "is
there some way to see what's going on" question ;)
> After all has settled, does:
> devkit-disks --dump
> print anything useful about this device?
Appended.
> Let's find some possible way to optimize this behavior. It seems all
> comes down to optimize the blkid usage, as HAL should go away (or at
> least get crippled not to matter anymore) before the next release
> anyway.
>
> How large is the volume? If it's very small, maybe we could add logic
> to skip the probing for any RAID stuff, which can not really exist on
> such small volumes.
It's tiny. It's half a megabyte - so the "read 120kB to figure out what
format it is" (ok, so blkid only reads ~70kB, but the kernel rounds it up)
is literally a quarter of the whole disk!
So in "how long does it take to read the whole disk" terms, this device
isn't all that slow.
> Should we disable or limit the read-ahead logic with BLKRASET? That
> might possibly cut the time down to the half, right?
I agree that maybe that could be a part of the answer (since we know that
read-ahead isn't going to help), but even just 70kB is quite a bit to read
when you get just 15kB/s or so.
It would likely cut down that 8+ seconds for that one long read to just
4.5s, but with all the other reads (blkid also probes at the end etc) it
would be closer to ten seconds (rather than the current 13s+) and then
doing it twice (once for the raw disk, once for the partition) would
_still_ be unbearably long.
So for something like this, that looks more like a partitioned (and slow)
floppy than anything else, the only real solution is to read much less.
Linus
---
..
.. deleted sda/sdb information - they're the internal disks ..
..
.. The problematic disk is sdc, and this also shows a workding
.. usb memory stick at sdd
..
========================================================================
Showing information for /org/freedesktop/DeviceKit/Disks/devices/sdc
native-path: /sys/devices/pci0000:00/0000:00:1d.1/usb3/3-1/3-1:1.0/host10/target10:0:0/10:0:0:0/block/sdc
device: 8:32
device-file: /dev/sdc
by-id: /dev/disk/by-id/usb-B-EMB_USB_RAM_Disk_INST_0-0:0
by-path: /dev/disk/by-path/pci-0000:00:1d.1-usb-0:1:1.0-scsi-0:0:0:0
detected at: Fri 15 Jan 2010 07:25:24 AM PST
system internal: 0
removable: 1
has media: 1 (detected at Fri 15 Jan 2010 07:25:24 AM PST)
detects change: 1
detection by polling: 1
detection inhibitable: 1
detection inhibited: 0
is read only: 0
is mounted: 0
mount paths:
mounted by uid: 0
presentation hide: 0
presentation nopolicy: 0
presentation name:
presentation icon:
size: 505856
block size: 512
job underway: no
usage:
type:
version:
uuid:
label:
partition table:
scheme: mbr
count: 1
drive:
vendor: B-EMB
model: USB RAM Disk
revision: 1.11
serial: INST_0
detachable: 1
can spindown: 0
rotational media: 1
ejectable: 0
media:
compat:
interface: usb
if speed: 12000000 bits/s
ATA SMART: not available
========================================================================
Showing information for /org/freedesktop/DeviceKit/Disks/devices/sdc1
native-path: /sys/devices/pci0000:00/0000:00:1d.1/usb3/3-1/3-1:1.0/host10/target10:0:0/10:0:0:0/block/sdc/sdc1
device: 8:33
device-file: /dev/sdc1
by-id: /dev/disk/by-id/usb-B-EMB_USB_RAM_Disk_INST_0-0:0-part1
by-path: /dev/disk/by-path/pci-0000:00:1d.1-usb-0:1:1.0-scsi-0:0:0:0-part1
detected at: Fri 15 Jan 2010 07:25:53 AM PST
system internal: 0
removable: 0
has media: 1 (detected at Fri 15 Jan 2010 07:25:53 AM PST)
detects change: 0
detection by polling: 0
detection inhibitable: 0
detection inhibited: 0
is read only: 0
is mounted: 0
mount paths:
mounted by uid: 0
presentation hide: 0
presentation nopolicy: 0
presentation name:
presentation icon:
size: 489472
block size: 512
job underway: no
usage: filesystem
type: vfat
version: FAT12
uuid:
label:
partition:
part of: /org/freedesktop/DeviceKit/Disks/devices/sdc
scheme: mbr
number: 1
type: 0x01
flags: boot
offset: 16384
size: 505344
label:
uuid:
========================================================================
Showing information for /org/freedesktop/DeviceKit/Disks/devices/sdd
native-path: /sys/devices/pci0000:00/0000:00:1d.7/usb1/1-4/1-4:1.0/host8/target8:0:0/8:0:0:0/block/sdd
device: 8:48
device-file: /dev/sdd
by-id: /dev/disk/by-id/usb-Generic_USB_Flash_Disk_00000000000B13-0:0
by-id: /dev/disk/by-uuid/2926-0CAA
by-path: /dev/disk/by-path/pci-0000:00:1d.7-usb-0:4:1.0-scsi-0:0:0:0
detected at: Thu 14 Jan 2010 03:43:37 PM PST
system internal: 0
removable: 1
has media: 1 (detected at Thu 14 Jan 2010 03:43:37 PM PST)
detects change: 1
detection by polling: 1
detection inhibitable: 1
detection inhibited: 0
is read only: 0
is mounted: 1
mount paths: /media/2926-0CAA
mounted by uid: 501
presentation hide: 0
presentation nopolicy: 0
presentation name:
presentation icon:
size: 2021654528
block size: 512
job underway: no
usage: filesystem
type: vfat
version: FAT16
uuid: 2926-0CAA
label:
drive:
vendor: Generic
model: USB Flash Disk
revision: 0.00
serial: 00000000000B13
detachable: 1
can spindown: 0
rotational media: 1
ejectable: 0
media:
compat:
interface: usb
if speed: 480000000 bits/s
ATA SMART: not available
========================================================================
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