Re: Btrfs Issues

[Ruoxin Jiang <rj2394@columbia.edu>]

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Hi Satoru,

I'm so sorry for the late reply! I rewrote the test programs to invoke
syscalls in the conventional way and added a few comments. Please find
attached the revised report.

As to your questions on "mmap", you are totally right that the first
mmap in the original 1/min.cpp is irrelevant. The original program was
automatically generated from a fuzzer I used and I hope the revised
ones to be much more understandable.

Thanks,
Amy

On Sun, Sep 17, 2017 at 11:10 PM, Satoru Takeuchi
<satoru.takeuchi@gmail.com> wrote:
> At Wed, 13 Sep 2017 11:53:35 -0400,
> Ruoxin Jiang wrote:
>>
>> [1  <text/plain; UTF-8 (7bit)>]
>> Hello,
>>
>> We are researchers from Columbia University, New York. As part of our
>> current research we have found some semantic discrepancies between
>> btrfs and other popular filesystems.
>>
>> We have attached two cases. The first one involves an invalid O_DIRECT
>> write() that fails back to buffered write instead of failing with
>> error EINVAL. In directory 2, we discovered that btrfs calculates
>> write_bytes in __btrfs_buffered_write differently from that in
>> generic_perform_writes in fs/mmap.c. This can cause inconsistent
>> behavior between btrfs and other filesystems when program invokes the
>> same writev/write() syscall.
>>
>> In each directory, you will find a Readme.md describing the issue and
>> pointing to the code that may cause the problem. For your convenience,
>> we also included test programs (min.cpp) and instructions in Readme to
>> help reproduce the issues.
>>
>> We would appreciate very much if you could confirm the two cases at
>> your conveniences.
>
> I took a look at your test programs, btrfs_issues/{1,2}/min.cpp. It looks
> very hard to read since you call syscalls in odd ways and all flags are
> hardcoded as literal hexadecimal numbers. Could rewrite these program
> to improve readability?
>
> In addition, I have two questions about btrfs_issues/1/min.cpp.
>
> 1. Why you set 'filename' as the 1st argument of mmap()?
> 2. What's the purpose of mmap() call? I guess mmap() is not related to issue 1.
>
> Thanks,
> Satoru
>
>>
>> Thanks,
>> Amy
>> [2 btrfs_issues.tar.gz <application/x-gzip (base64)>]
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-- 
Ruoxin(Amy) Jiang
Columbia University, M.S. Computer Science
347-277-5455

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