Fix #306

[taigrr]

Please see #306
The HEAD of main already fails existing test cases, and this patch causes those test cases to pass.

tai@juggernaut:~/code/foss/ghw/pkg/snapshot[jaypipes ?]$ go test
--- FAIL: TestCloneSystemTree (0.07s)
    clonetree_linux_test.go:85: Expected nil err, but got open /sys/devices/system/node/node0/hugepages/hugepages-1048576kB/demote: permission denied
FAIL
exit status 1
FAIL    github.com/jaypipes/ghw/pkg/snapshot    0.076s
tai@juggernaut:~/code/foss/ghw/pkg/snapshot[jaypipes ?]$ git co hugepages-demote
Switched to branch 'hugepages-demote'
Your branch is up to date with 'origin/hugepages-demote'.
tai@juggernaut:~/code/foss/ghw/pkg/snapshot[hugepages-demote ?]$ go test
PASS
ok      github.com/jaypipes/ghw/pkg/snapshot    0.100s
tai@juggernaut:~/code/foss/ghw/pkg/snapshot[hugepages-demote ?]$

[taigrr]

Looks like the project is using go <= 1.15. I'll update the code to be more backwards compatible.

[ffromani]

the proper fix would be to NOT copy the write-only files, we had some examples of this already. But we can improve later, this seems like a good enough fix. Thanks!

[taigrr]

Aha, I referenced the code here:

ghw/pkg/snapshot/clonetree_block_linux.go

Lines 122 to 130 in c82d7b1

	buf, err := ioutil.ReadFile(fp)
	if err != nil {
	if errors.Is(err, os.ErrPermission) {
	// example: /sys/devices/virtual/block/zram0/compact is 0400
	trace("permission denied reading %q - skipped\n", fp)
	continue
	}
	return err
	}

[ffromani]

Aha, I referenced the code here:

ghw/pkg/snapshot/clonetree_block_linux.go

Lines 122 to 126 in c82d7b1

	buf, err := ioutil.ReadFile(fp)
	if err != nil {
	if errors.Is(err, os.ErrPermission) {
	// example: /sys/devices/virtual/block/zram0/compact is 0400
	trace("permission denied reading %q - skipped\n", fp)

sure, again this fix is good! we can perhaps improve even more, but this can wait a bit. Better to have a working ghw-snapshot sooner than later.

If I get some more ghw time this week, I'll perhaps post a further refinement.

[jaypipes]

@taigrr hey, sorry for the late response here, just wanted to say thank you for the bug report and the fix! :)

[taigrr]

@jaypipes no worries, we got there :)