On Wednesday, 29 March 2017 11:04:09 CEST Гюльнара Невежина wrote:

 Many thanks for a quick reply,

 > see also
 > https://bugzilla.redhat.com/show_bug.cgi?id=1413499#c5

 Looks like the same issue as mine. But any way - a full log of
 guestmount, running it with -v -x and host + VM info are attached,
 probably I've missed something important in the output.

Indeed, the log shows that as well:

  mount -o ro /dev/sda2 /sysroot/
  [ 2.673870] SGI XFS with ACLs, security attributes, large block/inode numbers, no debug enabled
  [ 2.674968] SGI XFS Quota Management subsystem
  [ 2.675522] XFS (sda2): bad version
  [ 2.675754] XFS (sda2): SB validate failed
  mount: wrong fs type, bad option, bad superblock on /dev/sda2,
         missing codepage or helper program, or other error
         In some cases useful info is found in syslog - try
         dmesg | tail or so

  guestfsd: error: /dev/sda2 on / (options: 'ro'): mount: wrong fs type, bad option, bad superblock on /dev/sda2,
         missing codepage or helper program, or other error
         In some cases useful info is found in syslog - try
         dmesg | tail or so
  guestfsd: main_loop: proc 73 (mount_ro) took 0.07 seconds

so you need a RHEL/CentOS 7 (or another distro with a kernel >= 3.16)
to mount that XFS filesystem.
 

--
Pino Toscano