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SubjectRe: [PATCH v4 1/2] hugetlb: use f_mode & FMODE_HUGETLBFS to identify hugetlbfs files
On 6/15/20 1:24 AM, Miklos Szeredi wrote:
> On Sat, Jun 13, 2020 at 8:53 AM Amir Goldstein <> wrote:
>>> I also looked at normal filesystem lower and hugetlbfs upper. Yes, overlayfs
>>> allows this. This is somewhat 'interesting' as write() is not supported in
>>> hugetlbfs. Writing to files in the overlay actually ended up writing to
>>> files in the lower filesystem. That seems wrong, but overlayfs is new to me.
> Yes, this very definitely should not happen.
>> I am not sure how that happened, but I think that ovl_open_realfile()
>> needs to fixup f_mode flags FMODE_CAN_WRITE | FMODE_CAN_READ
>> after open_with_fake_path().
> Okay, but how did the write actually get to the lower layer?
> I failed to reproduce this. Mike, how did you trigger this?

My apologies!!!

I reviewed my testing and found that it was incorrectly writing to the
lower filesystem. Writing to any file in the union will fail.
Mike Kravetz

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