On 04/15/2016 04:48 AM, Dmitry Mishin wrote:
I am reviewing recent VZ7 libploop commits, in particular, this one:
https://src.openvz.org/projects/OVZ/repos/ploop/commits/36df847b9
I left a question there, let me repeat it here in a hope someone
answers.
Igor Sukhihcommitted36df847b99c
<https://src.openvz.org/projects/OVZ/repos/ploop/commits/36df847b99c92557c69255ebfb00d4cc74cb51ac>Yesterday
ploop_copy_init(): open folder with O_DIRECTORY flag
...
- _h->mntfd = open(mnt, O_RDONLY);
+ _h->mntfd = open(mnt, O_RDONLY|O_NONBLOCK|O_DIRECTORY);
1. What's the reason for adding O_NONBLOCK here? As far as I can
see, it doesn't
change anything at all (neither in this open(), nor in subsequent
syncfs(), ioctl()
and close())? I went as far as the kernel sources to check that
O_NONBLOCK
doesn't affect syncfs() call, but maybe I'm mistaken?
Added accidentally, you are right, it doesn't change anything.
2. What's the reason for adding O_DIRECTORY? Ideally, the changelog
should say why we're doing it, not what we do (as it's pretty clear
from the patch itself).
It does exactly as specified – enforces open file to be a directory.
See, I am not asking what it does -- it's pretty clear from open(2) man
page.
What I am interested in is the reason _why_ it was added. A bug report
this change is trying to fix, or a train of thought leading to this
change, etc.
Ideally this is what the changelog message should tell us.
Any problems with this enforcement?
No, I don't foresee any problems, more to say, this extra check might
actually do some good.
Kir.
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