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Date:   Sun, 7 Nov 2021 17:46:30 -0800
From:   Jeremy Allison <jra@samba.org>
To:     Steve French <smfrench@gmail.com>
Cc:     Julian Sikorski <belegdol@gmail.com>,
        CIFS <linux-cifs@vger.kernel.org>
Subject: Re: Permission denied when chainbuilding packages with mock
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On Sun, Nov 07, 2021 at 04:50:21PM -0600, Steve French wrote:
>That is interesting ... and weird.   Why would POSIX allow doing
>something write related (fsync) without write permission?

It's not POSIX, it's Linux :-).

It also operates on meta-data, so if the buffer cache
has any pending changes on a read-only fd, then fsync(fd)
will flush them.

man 2 fsync.

..
        As well as flushing the file data, fsync() also  flushes  the  metadata
        information associated with the file (see inode(7)).

I think cifsfs needs to keep track of the file modes
and silently return success on a read-only fd even
if mounted without nostrictsync.