Re: Btrfs Issues

[Satoru Takeuchi <satoru.takeuchi@gmail.com>]

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)>]