mfu: copy much more xattrs

[KoyamaSohei]

When copying files using dcp or dsync, extended attributes such as project id are also copied.

Resolves #553.

[ofaaland]

Thanks for your contribution @KoyamaSohei, I have one concern.

[KoyamaSohei]

@ofaaland Could you please review again?

I fixed to copy only fsx_projid and FS_XFLAG_PROJINHERIT

[ofaaland]

@KoyamaSohei Thanks for this improvement.

Please do some testing to and report the performance impact of your code change, preferably on a parallel file system like Lustre which may have high throughput but higher latency than something local like xfs.

Please also modify your commit message to reflect that mfu is copying projectid ; the commit message still makes it sounds like it's copying many xattrs.

[KoyamaSohei]

We compared the execution time when copying lustre-release 10 times on Lustre using dcp.

There was a significant decrease in performance ...

without projid	with projid
6.730	35.203
6.661	16.111
6.381	12.757
6.189	9.895
6.023	7.868
8.082	11.188
9.612	16.068
10.529	20.939
10.450	15.777
11.078	9.029

[ofaaland]

We compared the execution time when copying lustre-release 10 times on Lustre using dcp.

There was a significant decrease in performance ...
without projid with projid
6.730 35.203
6.661 16.111
6.381 12.757
6.189 9.895
6.023 7.868
8.082 11.188
9.612 16.068
10.529 20.939
10.450 15.777
11.078 9.029

I think we should try and fix that before we merge this. For our site, for example, we don't yet use projectid at all, so this would be a big performance hit for no benefit.

I wonder if this is because we are sort-of opening each file twice, once for getxattr(2) and once for open(2) in preparation for the ioctl(FS_IOC_FSGETXATTR). If that's true, refactoring the code to to call open once and then use that fd for both fgetxattr and ioctl might improve performance.

Before you do that refactoring work, though, maybe you can figure out with some careful experiments whether that's where the time is going, or whether we're spending it elsewhere.