From: Valerie Aurora <vaurora@redhat.com>
To: linux-fsdevel@vger.kernel.org
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
Erez Zadok <ezk@cs.sunysb.edu>,
"J. R. Okajima" <hooanon05@yahoo.co.jp>,
Christoph Hellwig <hch@infradead.org>
Subject: Union mounts and fchown/fchmod/utimensat
Date: Fri, 26 Mar 2010 18:45:34 -0400 [thread overview]
Message-ID: <20100326224533.GB29874@shell> (raw)
In the current union mount design, files that will be modified are
copied up from the lower layer file system to the top layer at open()
time. However, there are three cases in which metadata can be
modified through a file descriptor opened O_RDONLY: fchown(),
fchmod(), and utimensat(). Currently, we only copy up a file before
it is open, never after. Implementing these system calls would
require replacing the read-only open file descriptor from the lower
file system with a new file descriptor from the topmost layer - in
other words, a huge nasty hack.
My question: How often do applications actually attempt fchown(),
fchmod(), or utimensat() on an O_RDONLY file descriptor? Would it
break a lot of applications if a union mount file returned EBADF or
EPERM in this case?
-VAL
next reply other threads:[~2010-03-26 22:45 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-03-26 22:45 Valerie Aurora [this message]
2010-03-27 15:43 ` Union mounts and fchown/fchmod/utimensat J. R. Okajima
2010-03-29 18:39 ` Valerie Aurora
2010-03-29 23:48 ` Jamie Lokier
2010-03-30 11:16 ` Theodore Tso
2010-03-30 20:30 ` Valerie Aurora
2010-03-30 21:31 ` Valerie Aurora
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