linux-ext4 - Re: [RFC PATCH] ext4: add link file support for {GET,SET}XATTR ioctl

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Date:   Thu, 31 Jan 2019 14:41:06 +1100
From:   Dave Chinner <david@...morbit.com>
To:     Wang Shilong <wangshilong1991@...il.com>
Cc:     linux-ext4@...r.kernel.org, linux-fs@...r.kernel.org,
        linux-xfs@...r.kernel.org, Wang Shilong <wshilong@....com>,
        Andreas Dilger <adilger@...ger.ca>, Li Xi <lixi@....com>
Subject: Re: [RFC PATCH] ext4: add link file support for {GET,SET}XATTR ioctl

On Thu, Jan 31, 2019 at 10:47:12AM +0900, Wang Shilong wrote:
> From: Wang Shilong <wshilong@....com>
> 
> Currently there is no way to change project ID of
> symlink file itself, this is important to implement
> Directory quota for an existed directory.

This seems like something open(O_PATH|O_NOFOLLOW) should allow.
from open(2):

	If pathname is a symbolic link and the O_NOFOLLOW flag is
	also specified, then the call returns a file  descriptor
	referring  to  the symbolic  link.  This  file  descriptor
	can  be used as the dirfd argument in calls to fchownat(2),
	fstatat(2), linkat(2), and read¿ linkat(2) with an empty
	pathname to have the calls operate on the symbolic link.

Changing the project id is the equivalent of fchownat().....

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com