LTP: fix test case fchown04 issue

[shaikshavali1]

The original test case performs the below tests:

1. fchown(2) returns -1 and sets errno to EPERM if the effective
   user id of the process does not match the owner of the file
   and the process is not a superuser.
2. fchown(2) returns -1 and sets errno to EBADF if the file
   descriptor of the specified file is not valid.
3. fchown(2) returns -1 and sets errno to EROFS if the named file
   resides on a read-only file system.

Problem/issue:
This test case causing oom killer to be invoked and causing
kernel panic. This is because the test case invokes test framework
function "tst_acquire_device" which creates a 256MB of .img file
and binds with a loop device. This is not supported because the
default size of LKL memory is set to 32M. This is kept low due to
the limited size of EPC (Enclave page cache) and to avoid page
cache being swapped out.
Also, the test case invokes "tst_mkfs" framework function which
inturn invokes mkfs utility command with the help of system() syscall.
It is recommended to use root file system, but, this test case
needs a read-only filesystem to test one of the sub-test case.
we don't have a read-only file system mounted in sgx-lkl.
Hence, disabling the code related to the mount and sub test case.

Modifications:

1. Disable the 3rd subtest case
2. Disable the code which creates file system, mount, and unmount the filesystem.
   Review-1:
3. Added the code to create a loop device and mount. This need some changes to lsds/sgx-lkl repo, new PR is raised LTP: Pass ext4 block device to enclave sgx-lkl#764
4. Enabled the 3rd sub test case.

[davidchisnall]

I still believe that the correct way of fixing tests like this is to add either partitions or separate block devices to our test environment that provide the required file systems. We could easily add a separate 256MB block device for tests like this and do the mkfs on the outside.

[SeanTAllen]

This needs a corresponding PR on sgx-lkl so that CI is run with this change. Please speak to @hukoyu if you aren't familiar with how to do that.

[shaikshavali1]

I still believe that the correct way of fixing tests like this is to add either partitions or separate block devices to our test environment that provide the required file systems. We could easily add a separate 256MB block device for tests like this and do the mkfs on the outside.

@davidchisnall, Is this below approach is fine.

1. create a disk image file in sgxlkl-miniroot-fs.img.master
   dd if=/dev/zero of=testfs_ext4.img bs=1M count=265
2. format this to ext4
   mkfs -t ext4 testfs_ext4.img
3. Update the Framework/test case to pick this testfs_ext4.img and bind it with any available loop device.
4. mount this loop device in the test case and perform the test.

[prp]

Why do you want to use a loop device here? Can't you mount a separate block device using SGX-LKL, similar to what we do in some of our other CI tests?

[shaikshavali1]

@davidchisnall, @prp, I updated the changes as per your suggestion. In this PR and PR: lsds/sgx-lkl#750

[hukoyu]

LGTM. After lsds/sgx-lkl#764 and #65 are merged this fix will work.

[hukoyu]

LGTM. After lsds/sgx-lkl#764 and #65 are merged this fix will work.

@davidchisnall both of dependent PRs merged. This PR is ready to be merged if you approve.