-----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----- _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Samuel Thibault
2008-Jul-11 10:23 UTC
Re: [Xen-devel] Tapdisk O_DIRECT breaks read-only-ness
Christopher Head, le Thu 10 Jul 2008 21:02:06 -0700, a écrit :> 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.tapdisk: in case O_DIRECT fails, retry again with o_flags but O_DIRECT, instead of fixed value O_RD_WR | O_LARGEFILE Signed-off-by: Samuel Thibault <samuel.thibault@eu.citrix.com> diff -r 06d80308aa2e tools/blktap/drivers/block-sync.c --- a/tools/blktap/drivers/block-sync.c Thu Jul 10 19:23:55 2008 +0100 +++ b/tools/blktap/drivers/block-sync.c Fri Jul 11 11:21:58 2008 +0100 @@ -129,7 +129,7 @@ /* Maybe O_DIRECT isn''t supported. */ o_flags &= ~O_DIRECT; - fd = open(name, O_RDWR | O_LARGEFILE); + fd = open(name, o_flags); if (fd != -1) DPRINTF("WARNING: Accessing image without" "O_DIRECT! (%s)\n", name); _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel