Re: dracut does not mount iscsi targets specified using --mount option

[Cong Wang <amwang-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On Fri, 2012-04-20 at 09:51 -0400, Vivek Goyal wrote:
> On Thu, Apr 19, 2012 at 10:59:17AM +0200, Harald Hoyer wrote:
> > Am 19.04.2012 00:28, schrieb Vivek Goyal:
> > > Hi,
> > > 
> > > I am trying to dump kernel vmcore to an software iscsi target (kdump).
> > > kdump specifies the dump destination using "--mount" option. But dracut
> > > does not even include the "iscsi" module and associated device is not
> > > mounted in second kernel.
> > > 
> > > Following is the dracut command line as called by /sbin/mkdumprd.
> > > 
> > > dracut -m kdumpbase --add dash --add fstab-sys --add kernel-modules -c /dev/null -I /sbin/makedumpfile --mount '/dev/mapper/vg-lv_root / ext4 rw,seclabel,relatime,user_xattr,barrier=1,data=ordered' --mount '/dev/mapper/mpatha /mnt/common ext4 rw,seclabel,relatime,user_xattr,barrier=1,stripe=16,data=ordered' -M -f /boot/initramfs-3.3.2-1.fc17.x86_64kdump.img 3.3.2-1.fc17.x86_64
> > 
> > "-m kdumpbase" - This tells dracut to only use the kdumpbase dracut module
> > So, because the iscsi dracut module is not added, dracut does not even check() it.
> > 
> > Why is it "-m kdumpbase" and not "--add kdumpbase" ???
> 
> I don't know why -m is being used instead of --add. I tried changing it
> to --add and uncompressed initramfs size changed from 36MB to 72MB.
> 
> To me 32MB size itself is big. IIRc, in RHEL6 using our own mkinitrd, we had
> uncomressed initrd size close to 25MB.
> 
> In kdump environment we work in very restricted memory conditions.
> Currently we reserve 128MB and there are calls to reduce it further. This
> 128MB should load kernel, initramfs and run all the tools in initramfs
> to actually save the vmcore to the target.
> 
> So we need to figure out how can we reduce the size of initramfs for
> kdump case. In the next mail I will add the output of --debug both for
> -m kdumpbase and --add kdumpbase.
> 
> From kdump perspective, we only need to mount targets as specified by
> --mount option. We might not want to mount even root and it depends on
> kdump.conf. If root is needed, we will pass that too on command line
> using --mount. So this is little different from -H option.
> 
> Can we modify dracut in such a way so that it packs only those modules
> need to mount targets as specified --mount options?

Yeah, I noticed this too, I think this is due to the dracut module
"kernel-modules" includes more than enough kernel modules into
initramfs, thus the size increased so much.

Harald, if you have any idea to improve this? We need to find a way to
tell "kernel-modules" module to only include the ones we want.

Thanks.