On Wed, Nov 1, 2017 at 4:42 PM, Vivek Goyal <vgoyal@xxxxxxxxxx> wrote:
> On Mon, Oct 30, 2017 at 10:27:25PM +0200, Amir Goldstein wrote:
>> From: Chandan Rajendra <chandan@xxxxxxxxxxxxxxxxxx>
>>
>> For stat(2) on lowerdir non-dir entries in non-samefs case, this commit
>> provides unique values for st_dev. The unique values are obtained by
>> allocating anonymous bdevs for each of the lowerdirs in the overlayfs
>> instance.
>
> Hi Amir, Chandan,
>
> In the commit message, can we also mention what's the current behavior
> and why this new behavior beneficial/desirable.
>
This is the blurb from the uptodate patch on my branch:
For non-samefs setup, to make sure that st_dev/st_ino pair
is unique across the system, we return a unique anonymous
st_dev for stat(2) of lower layer inode.
A bit fatter, but not fat enough...
Actually, it is not accurate, because st_dev/st_ino pair of pure
upper is still same values as underlying inode for non-samefs so the
values are not unique among all inodes in the system.
I can't remember if there was a reason for not allocating anonymous bdev
for upper or if it just because we did not need it to guaranty uniqueness
of st_dev/st_ino *among* overlay inodes while guarantying constant
st_dev/st_ino across copy up.
I will update commit message.
Thanks,
Amir.
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