Hmm .. kernel bug perhaps?  Does using the -v option provide
any more information?

It works for me on Fedora 19 / libguestfs 1.23.22, although
that doesn't really mean much.

Some other questions:

 - How was the ISO file prepared?  Perhaps the ISO is faulty.

 - Does the following command work on the host:
   mkdir /tmp/loop; mount -o loop file.iso /tmp/loop

I can reproduce this with:

kernel-3.10.0-29.el7.x86_64
libguestfs-1.22.6-8.el7.x86_64

The reproducer is:

$ mkdir /tmp/empty
$ genisoimage -o /tmp/test.iso /tmp/empty
$ guestfish -v -N fs -m /dev/sda1 upload /tmp/test.iso /test.iso : mkdir /loop : mount-loop /test.iso /loop

There's not very much information in the verbose output, in
particular no kernel error messages, just:

mount -o loop /sysroot/test.iso /sysroot/loop
mount: /sysroot/test.iso: failed to setup loop device: No such file or directory
guestfsd: error: /test.iso on /loop: mount: /sysroot/test.iso: failed to setup loop device: No such file or directory
libguestfs: error: mount_loop: /test.iso on /loop: mount: /sysroot/test.iso: failed to setup loop device: No such file or directory
libguestfs: closing guestfs handle 0x7f4e38a75bb0 (state 2)
guestfsd: main_loop: proc 129 (mount_loop) took 0.07 seconds
guestfsd: main_loop: new request, len 0x28

Same, in virt-rescue:

><rescue> mkdir /tmp/empty
><rescue> genisoimage -o /tmp/test.iso /tmp/empty
Total translation table size: 0
Total rockridge attributes bytes: 0
Total directory bytes: 0
Path table size(bytes): 10
Max brk space used 0
174 extents written (0 MB)
><rescue> mkdir /tmp/loop
><rescue> mount -o loop /tmp/test.iso /tmp/loop
mount: /tmp/test.iso: failed to setup loop device: No such file or directory

stracing the final command in virt-rescue shows the real error
is lack of /dev/loop devices:

readlink("/tmp", 0x7fffea3fe610, 4096)  = -1 EINVAL (Invalid argument)
readlink("/tmp/loop", 0x7fffea3fe610, 4096) = -1 EINVAL (Invalid argument)
readlink("/dev", 0x7fffea3fe610, 4096)  = -1 EINVAL (Invalid argument)
readlink("/run", 0x7fffea3fe610, 4096)  = -1 EINVAL (Invalid argument)
readlink("/sys", 0x7fffea3fe610, 4096)  = -1 EINVAL (Invalid argument)
readlink("/proc", 0x7fffea3fe610, 4096) = -1 EINVAL (Invalid argument)
stat("/dev/loop", 0x7fffea4005f0)       = -1 ENOENT (No such file or directory)
stat("/dev/loop0", 0x7fffea3ff540)      = -1 ENOENT (No such file or directory)
open("/sys/block/loop0/dev", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
readlink("/tmp", 0x7fffea3fe650, 4096)  = -1 EINVAL (Invalid argument)
readlink("/tmp/test.iso", 0x7fffea3fe650, 4096) = -1 EINVAL (Invalid argument)
open("/tmp/test.iso", O_RDWR|O_CLOEXEC) = 3
open("/dev/loop0", O_RDWR|O_CLOEXEC)    = -1 ENOENT (No such file or directory)
close(3)                                = 0
write(2, "mount: ", 7mount: )                  = 7
write(2, "/tmp/test.iso: failed to setup l"..., 42/tmp/test.iso: failed to setup loop device) = 42
write(2, ": ", 2: )                       = 2
write(2, "No such file or directory\n", 26No such file or directory
) = 26

><rescue> ls -l /dev/loop*
ls: cannot access /dev/loop*: No such file or directory
><rescue> ls -l /sys/block/loop*
ls: cannot access /sys/block/loop*: No such file or directory

Loading the kernel module explicitly makes it work:

><rescue> modprobe loop
[  159.545716] loop: module loaded
><rescue> mount -o loop /tmp/test.iso /tmp/loop

So the question would be why the kernel module needs to be
loaded explicitly or isn't loaded automatically?

kmod/systemd playing silly buggers again.  Here is the fix:

https://github.com/libguestfs/libguestfs/commit/e2895b19bb2be67c01172cdd0634553c21923605

Verified with libguestfs-1.22.6-16.el7.x86_64

$ mkdir /tmp/empty
$ genisoimage -o /tmp/test.iso /tmp/empty
$ guestfish -v -N fs -m /dev/sda1 upload /tmp/test.iso /test.iso : mkdir /loop : mount-loop /test.iso /loop


Execute no error

This request was resolved in Red Hat Enterprise Linux 7.0.

Contact your manager or support representative in case you have further questions about the request.