From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christopher Head Subject: Tapdisk O_DIRECT breaks read-only-ness Date: Thu, 10 Jul 2008 21:02:06 -0700 Message-ID: <4876DB3E.2060707@cs.ubc.ca> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hi all, It looks like some time ago a patch was applied to the Tapdisk backend drivers to add O_DIRECT to the open system calls whenever possible. However, on line 141 of tools/blktap/drivers/block-sync.c, at least as of revision 16947:f66bb3b80661 of Xen 3.2, it looks like there's a slight logic error: this line is where the open() system call is repeated without O_DIRECT (in case O_DIRECT fails), but instead of passing in o_flags as the second parameter, O_RDWR|O_LARGEFILE is passed directly. This means that if tap:sync is unable to open a file with O_DIRECT, it will then attempt to open the file read-write even if the original request was for a read-only open. Chris -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.9 (GNU/Linux) Comment: GnuPT 2.7.2 Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iEYEARECAAYFAkh22z0ACgkQiD2svb/jCb7WMACbBCK02IfXqXJ76X1gZHgdFUM8 y/QAoJGIuljAh1O/tNBD5zeuMlxU8Om7 =kp2J -----END PGP SIGNATURE-----