udev/modprobe issue

udev/modprobe issue

[Nico Schottelius]

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Good morning everybody!

I've a small problem with loading the sata_sil module, but it could be a
general issue: We use this sata-kontroller with sata-harddisks to backup
our systems. The harddisk is exchanged (while the system is running) every
day. So we load/unload sata_sil in our backup scripts, so 'hotplugging' is possible.

My problem is, that modprobe returns earlier than the attached device is usable:

----------------------------------------------------------------------
srwali01:/# modprobe sata_sil; mount /dev/sda1 /mnt/hdbackup/
mount: you must specify the filesystem type
srwali01:/# rmmod sata_sil
srwali01:/# modprobe sata_sil; ls -l /dev/sda1               
ls: /dev/sda1: No such file or directory
----------------------------------------------------------------------

So I have to do

----------------------------------------------------------------------
srwali01:/# modprobe sata_sil
srwali01:/# sleep 2
srwali01:/# mount /dev/sda1 /mnt/hdbackup
----------------------------------------------------------------------

The problem is most likely that udev is too slow or that modprobe does not
know/wait for udev:

----------------------------------------------------------------------
srwali01:/# mount | grep tmpfs | grep -v /dev/shm
tmpfs on /dev type tmpfs (rw,size=10M,mode=0755)
srwali01:/# cat /proc/sys/kernel/hotplug 
/sbin/udevsend
----------------------------------------------------------------------

My questions:

- Should modprobe wait for whatever current hotplug is so that
  the system can definitly use the device after modprobe?
- Or should there be a command-line switch to modprobe to tell it to wait
  for hotplug?
- Is the 'wait for hotplug'-idea possible to do or would it have to be a dirty
  hack in the kernel?
- Is there clean solution to wait exactly as long as
  it needs to load sata_sil and create /dev/sda*?
  Using while+ls monitoring /dev/sda* is not a solution imho.

Greetings,

Nico

P.S.: Sorry for crossposting, I am not really sure which list would have been
      the correct one to ask.

-- 
Latest project: cconfig (http://nico.schotteli.us/papers/linux/cconfig/)
Open Source nutures open minds and free, creative developers.

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Re: udev/modprobe issue

[Kay Sievers]

On Thu, Sep 29, 2005 at 09:41:40AM +0200, Nico Schottelius wrote:
> Good morning everybody!
> 
> I've a small problem with loading the sata_sil module, but it could be a
> general issue: We use this sata-kontroller with sata-harddisks to backup
> our systems. The harddisk is exchanged (while the system is running) every
> day. So we load/unload sata_sil in our backup scripts, so 'hotplugging' is possible.
> 
> My problem is, that modprobe returns earlier than the attached device is usable:
> 
> ----------------------------------------------------------------------
> srwali01:/# modprobe sata_sil; mount /dev/sda1 /mnt/hdbackup/
> mount: you must specify the filesystem type
> srwali01:/# rmmod sata_sil
> srwali01:/# modprobe sata_sil; ls -l /dev/sda1               
> ls: /dev/sda1: No such file or directory
> ----------------------------------------------------------------------
> 
> So I have to do
> 
> ----------------------------------------------------------------------
> srwali01:/# modprobe sata_sil
> srwali01:/# sleep 2
> srwali01:/# mount /dev/sda1 /mnt/hdbackup
> ----------------------------------------------------------------------
> 
> The problem is most likely that udev is too slow or that modprobe does not
> know/wait for udev:
> 
> ----------------------------------------------------------------------
> srwali01:/# mount | grep tmpfs | grep -v /dev/shm
> tmpfs on /dev type tmpfs (rw,size\x10M,mode\a55)
> srwali01:/# cat /proc/sys/kernel/hotplug 
> /sbin/udevsend
> ----------------------------------------------------------------------
> 
> My questions:
> 
> - Should modprobe wait for whatever current hotplug is so that
>   the system can definitly use the device after modprobe?

No.

> - Or should there be a command-line switch to modprobe to tell it to wait
>   for hotplug?

No.

> - Is the 'wait for hotplug'-idea possible to do or would it have to be a dirty
>   hack in the kernel?

Not possible.

> - Is there clean solution to wait exactly as long as
>   it needs to load sata_sil and create /dev/sda*?
>   Using while+ls monitoring /dev/sda* is not a solution imho.

Wait for the node, or use the device event the kernel generates for the device
you're looking for. You can catch it with a udev rule.

Kay


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Re: udev/modprobe issue

[Nico -telmich- Schottelius]

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Kay Sievers [Fri, Sep 30, 2005 at 07:12:26PM +0200]:
> [...] 
> > - Is there clean solution to wait exactly as long as
> >   it needs to load sata_sil and create /dev/sda*?
> >   Using while+ls monitoring /dev/sda* is not a solution imho.
> 
> Wait for the node, or use the device event the kernel generates for the device
> you're looking for. You can catch it with a udev rule.

Could you throw some RTFM to me so I know which device to listen to
and howto implement that in a shell script?

Nico

-- 
Latest project: cconfig (http://nico.schotteli.us/papers/linux/cconfig/)
Open Source nutures open minds and free, creative developers.

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