fadump: fix dump capture failure to root disk
    
    Resolves: bz1952652
    Upstream: fedora
    Conflict: none
    
    commit d0e9c51e0de57273a99af8484515f213b8414e65
    Author: Hari Bathini <hbathini@linux.ibm.com>
    Date:   Thu Apr 22 18:21:59 2021 +0530
    
        fadump: fix dump capture failure to root disk
    
        If the dump target is the root disk, kdump scripts add an entry in
        /etc/fstab for root disk with /sysroot as the mount point. The root
        disk, passed through root=<> kernel commandline parameter, is mounted
        at /sysroot in read-only mode before switching from initial ramdisk.
        So, in fadump mode, a remount of /sysroot to read-write mode is needed
        to capture dump successfully, because /sysroot is already mounted as
        read-only based on root=<> boot parameter.
    
        Commit e8ef4db8ff91 ("Fix dump_fs mount point detection and fallback
        mount") removed initialization of $_op variable, the variable holding
        the options the dump target was mounted with, leading to the below
        error as remount was skipped:
    
          kdump[586]: saving to /sysroot/var/crash/127.0.0.1-2021-04-22-07:22:08/
          kdump.sh[587]: mkdir: cannot create directory '/sysroot/var/crash/127.0.0.1-2021-04-22-07:22:08/': Read-only file system
          kdump[589]: saving vmcore failed
    
        Restore $_op variable initialization in dump_fs() function to fix this.
    
        Fixes: e8ef4db8ff91 ("Fix dump_fs mount point detection and fallback mount")
        Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
        Acked-by: Kairui Song <kasong@redhat.com>
    
    Signed-off-by: Tao Liu <ltao@redhat.com>