[linux-lvm] determing lvm support

[linux-lvm] determing lvm support

[Rich Turner]

is there any fool proof way of knowing whether or not a system has lvm
support?

right now i determine it this way:

lvm1:
look for "vgcreate" command and
look for "lvm" in /proc/devices or
look for "lvm-mod" in /lib/modules/[release]/kernel/drivers/md/*

lvm2:
look for "vgcreate" command and
look for "device-mapper" in /proc/devices or
look for "dm-mod" in /lib/modules/[release]/kernel/drivers/md/*

i think i am fairly certain with lvm1, but with lvm2 i am not sure if i
have device mapper support and a lvm command that is enough.

any ideas?

rich turner

Re: [linux-lvm] determing lvm support

[Alasdair G Kergon]

On Fri, Dec 19, 2003 at 04:47:18PM -0800, Rich Turner wrote:
> lvm2:
> look for "vgcreate" command and
Better to check for the new 'lvm' base command: other commands are
links to it: check that running 'lvm version' produces complete output.
That will also confirm that device-mapper is available in the live
kernel and that /dev/mapper/control is set up correctly.
(See device-mapper/scripts/devmap_mknod.sh)

> look for "device-mapper" in /proc/devices or
It's better to check for that in /proc/misc, which will tell you whether
or not device-mapper support is present in the running kernel.

> look for "dm-mod" in /lib/modules/[release]/kernel/drivers/md/*
Better to attempt to load the module with modprobe and then do the
tests above to check it worked.
 
Alasdair
-- 
agk@uk.sistina.com

Re: [linux-lvm] determing lvm support

[Luca Berra]

On Sat, Dec 20, 2003 at 12:30:23PM +0000, Alasdair G Kergon wrote:
>On Fri, Dec 19, 2003 at 04:47:18PM -0800, Rich Turner wrote:
>> lvm2:
>> look for "vgcreate" command and
>Better to check for the new 'lvm' base command: other commands are
>links to it: check that running 'lvm version' produces complete output.
>That will also confirm that device-mapper is available in the live
>kernel and that /dev/mapper/control is set up correctly.
>(See device-mapper/scripts/devmap_mknod.sh)
>
Besides that is there any way to reliably check if dm is loaded from a
c program, besides calling dm_task_run(), which is noisy if the driver
is not loaded? I don't want the user to see an error if she's not
running device-mapper.
it the moment i try to open dm_dir()/control, is that ok?

L.

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Luca Berra -- bluca@comedia.it
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Re: [linux-lvm] determing lvm support

[Micah Anderson]

On Fri, 19 Dec 2003, Rich Turner wrote:

> is there any fool proof way of knowing whether or not a system has lvm
> support?
> 
> right now i determine it this way:
> 
> lvm1:

> look for "lvm-mod" in /lib/modules/[release]/kernel/drivers/md/*

> lvm2:
> look for "dm-mod" in /lib/modules/[release]/kernel/drivers/md/*

The only problem with this step is that many kernels (any
production-level server of mine at least) do not use loadable modules,
but instead build LVM support striaght into the kernel. In these cases
your tests for the modules will fail. 

Re: [linux-lvm] determing lvm support

[Alasdair G Kergon]

On Sat, Dec 20, 2003 at 02:35:41PM +0100, Luca Berra wrote:
> Besides that is there any way to reliably check if dm is loaded from a
> c program, besides calling dm_task_run(), which is noisy if the driver
> is not loaded? I don't want the user to see an error if she's not
> running device-mapper.

Look at using dm_log_init() to provide a function that
suppresses all output.

> it the moment i try to open dm_dir()/control, is that ok?
That should work OK bypassing libdevmapper.
Otherwise, try dm_task_get_driver_version() after disabling log output.
 
Alasdair
-- 
agk@uk.sistina.com

Re: [linux-lvm] determing lvm support

[Luca Berra]

On Sat, Dec 20, 2003 at 11:30:51PM +0000, Alasdair G Kergon wrote:
>On Sat, Dec 20, 2003 at 02:35:41PM +0100, Luca Berra wrote:
>> Besides that is there any way to reliably check if dm is loaded from a
>> c program, besides calling dm_task_run(), which is noisy if the driver
>> is not loaded? I don't want the user to see an error if she's not
>> running device-mapper.
>
>Look at using dm_log_init() to provide a function that
>suppresses all output.
I'll look at it, but it seems i cannot restore the previous log function
then, i think it's easier to bypass the lib for my particular case.
Thanks a lot for your answers.

Regards,
L.


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Luca Berra -- bluca@comedia.it
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Re: [linux-lvm] determing lvm support

[Alasdair G Kergon]

On Sun, Dec 21, 2003 at 09:08:02AM +0100, Luca Berra wrote:
> >Look at using dm_log_init() to provide a function that
> I'll look at it, but it seems i cannot restore the previous log function
I'll fix it so people can.

Alasdair
-- 
agk@uk.sistina.com

Re: [linux-lvm] determing lvm support

[Rich Turner]

On Sat, 2003-12-20 at 04:30, Alasdair G Kergon wrote:
> On Fri, Dec 19, 2003 at 04:47:18PM -0800, Rich Turner wrote:
> > lvm2:
> > look for "vgcreate" command and
> Better to check for the new 'lvm' base command: other commands are
> links to it: check that running 'lvm version' produces complete output.
> That will also confirm that device-mapper is available in the live
> kernel and that /dev/mapper/control is set up correctly.
> (See device-mapper/scripts/devmap_mknod.sh)
if i have 'device-mapper' and 'lvm version' produces complete output, is
there anything else to check if lvm is supported on the system?

is 'device-mapper' used for anything else besides lvm?

does the kernel need to be built with 'lvm' support (which i believe was
true with lvm1-created 'lvm-mod'), or does building a kernel for 'lvm'
support just create 'dm-mod' loadable module/builtin 'dm-mod' kernel
support?

> > look for "device-mapper" in /proc/devices or
> It's better to check for that in /proc/misc, which will tell you whether
> or not device-mapper support is present in the running kernel.
why is it better to check in /proc/misc? when device-mapper support is
loaded, it shows up in both /proc/misc as well as /proc/devices.

> 
> > look for "dm-mod" in /lib/modules/[release]/kernel/drivers/md/*
> Better to attempt to load the module with modprobe and then do the
> tests above to check it worked.
>  
> Alasdair

Re: [linux-lvm] determing lvm support

[Alasdair G Kergon]

On Mon, Dec 22, 2003 at 08:03:34AM -0800, Rich Turner wrote:
> > > look for "device-mapper" in /proc/devices or
> > It's better to check for that in /proc/misc, which will tell you whether
> > or not device-mapper support is present in the running kernel.
> why is it better to check in /proc/misc? when device-mapper support is
> loaded, it shows up in both /proc/misc as well as /proc/devices.

You can only guarantee its appearance in /proc/devices while you
have a device active.

Alasdair
-- 
agk@uk.sistina.com