Re: [PATCH 0/4] Dump core correctly to the bind mounted target

[Dave Young]

On 03/04/15 at 01:07am, Minfei Huang wrote:
> Enhance kdump to support bind mounted target, since kdump cann't parse
> the bind mounted path.
>
> Following is the testcases which kdump can generate the core sucessfully.
> rootfs, default path / specified path
> rootfs with bind mounted path which is in the rootfs device
>    # cat /etc/kdump | grep ^path
>    path /var/crash
>    # mount -o bind /var/crash /mnt/crash
> rootfs with bind mounted path which is not in the rootfs device
>    # cat /etc/kdump | grep ^path
>    path /var/crash
>    # mount /dev/vdb /mnt
>    # mount -o bind /var/crash /mnt/crash
> no-rootfs
> no-rootfs with bind mounted path which is in the same device
> no-rootfs with bind mounted path which is not in the same device
> nfs
> nfs with bind mounted path which is under the nfs mount point path
>    # cat /etc/kdump | grep ^nfs
>    nfs 192.168.122.134:/opt/crash
>    # cat /etc/kdump | grep ^path
>    path /var/crash
>    # mount.nfs 192.168.122.134:/opt/crash /mnt/nfs
>    # mount -o bind /mnt/nfs/var/crash /mnt/nfs/dump
> nfs with bind mounted path which is not under the nfs mount point path
>    # cat /etc/kdump | grep ^nfs
>    nfs 192.168.122.134:/opt/crash
>    # cat /etc/kdump | grep ^path
>    path /var/crash
>    # mount.nfs 192.168.122.134:/opt/crash /mnt/nfs
>    # mount -o bind /mnt/nfs/var/crash /mnt/dump
> nfs which don't specify the nfs option in the /etc/kdump, with bind mounted path which is under the nfs mount point path 
>    # cat /etc/kdump | grep ^nfs
>    # mount.nfs 192.168.122.134:/opt/crash /mnt/nfs
>    # cat /etc/kdump | grep ^path
>    path /mnt/nfs/var/crash
>    # mount -o bind /mnt/nfs/var/crash /mnt/nfs/dump
> nfs which don't specify the nfs option in the /etc/kdump, with bind mounted path which is not under the nfs mount point path 
>    # cat /etc/kdump | grep ^nfs
>    # mount.nfs 192.168.122.134:/opt/crash /mnt/nfs
>    # cat /etc/kdump | grep ^path
>    path /mnt/nfs/var/crash
>    # mount -o bind /mnt/nfs/var/crash /mnt/dump
> ext4
> ext4 with bind mounted path which is under the ext4 mount point path
> ext4 with bind mounted path which is not under the ext4 mount point path
> btrfs
> btrfs with subvolume which mounts under mount point path
> btrfs with subvolume which does not mount under mount point path
>
> Minfei Huang (4):
>   kdump-lib: Add new function to cut out the substring
>   kdump-lib: Add the new function to enhance bind mounted judgement
>   kdump-lib: Get the mount point correctly, if the device has several
>     mount point
>   dracut-module-setup: Fix the incorrect dumping target, if the path is
>     bind mounted
>
> dracut-module-setup.sh | 49 +++++++++++++++++++++++++++++++++++-----
>  kdump-lib.sh           | 61 +++++++++++++++++++++++++++++++++++++++++++++++++-
>  mkdumprd               | 32 +++++++++++++++++++-------
>  3 files changed, 128 insertions(+), 14 deletions(-)

There's some problems ie. umount original directory and only keep bind mounted one.

The cases looks complicated, I agree with Bao that it increases code complexity
dramaticlly so how about do it like below:

1) document that we do not support bind mount
2) for atomic, two ways to resolve the problem:
   *) they can pack a different kdump.conf with different default path 
   *) we can fix it by conditionally set default path for atomic

Thanks
Dave