From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Richard Weinberger Subject: Re: [uml-devel] [PATCH 1/1] hostfs: fix UML crash Date: Mon, 18 Oct 2010 22:03:42 +0200 References: <1287419814-20086-1-git-send-email-richard@nod.at> <201010182131.33385.richard@nod.at> In-Reply-To: MIME-Version: 1.0 Content-Type: Text/Plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <201010182203.42690.richard@nod.at> To: Geert Uytterhoeven Cc: Andrew Morton , toralf.foerster@gmx.de, jdike@addtoit.com, linux-kernel@vger.kernel.org, user-mode-linux-devel@lists.sourceforge.net, viro@zeniv.linux.org.uk List-ID: Am Montag 18 Oktober 2010, 21:43:44 schrieb Geert Uytterhoeven: > On Mon, Oct 18, 2010 at 21:31, Richard Weinberger wrote: > > Am Montag 18 Oktober 2010, 21:22:31 schrieb Geert Uytterhoeven: > >> On Mon, Oct 18, 2010 at 20:40, Andrew Morton > > > > wrote: > >> > On Mon, 18 Oct 2010 18:36:54 +0200 Richard Weinberger > > > > wrote: > >> >> 365b1818 resized f_spare within struct statfs. > >> >> hostfs accesses f_spare directly and needs an update. > >> >> > >> >> Signed-off-by: Richard Weinberger > >> >> Reported-by: Toralf F__rster > >> >> Tested-by: Toralf F__rster > >> >> --- > >> >> fs/hostfs/hostfs_user.c | 2 +- > >> >> 1 files changed, 1 insertions(+), 1 deletions(-) > >> >> > >> >> diff --git a/fs/hostfs/hostfs_user.c b/fs/hostfs/hostfs_user.c > >> >> index 6777aa0..ce2f168 100644 > >> >> --- a/fs/hostfs/hostfs_user.c > >> >> +++ b/fs/hostfs/hostfs_user.c > >> >> @@ -388,6 +388,6 @@ int do_statfs(char *root, long *bsize_out, long > >> >> long *blocks_out, spare_out[1] = buf.f_spare[1]; > >> >> spare_out[2] = buf.f_spare[2]; > >> >> spare_out[3] = buf.f_spare[3]; > >> >> - spare_out[4] = buf.f_spare[4]; > >> >> + > >> >> return 0; > >> >> } > >> > > >> > Thanks. > >> > > >> > Is there any reason for hostfs to be playing with the f_spare field at > >> > all? > >> > >> It just copies it from struct statfs64 on the host to struct kstatfs > >> on the guest. > >> Probably a memcpy() is more future-safe, if it's combined with a > >> BUILD_BUG_ON(sizeof(statfs64.f_spare) != sizeof(kstatfs.f_spare)). > >> > >> Still, currently it doesn't copy the recently added f_flags field. > >> To protect against future changes like that, an explicit > >> BUILD_BUG_ON(sizeof(kstatfs.f_spare) != 4*sizeof(long)) may be even > >> better... IMHO using kstatfs within ubd_user.c is not very nice because is a internal kernel struct. > > Anyway, why do we need to copy f_spare from the host to the guest? > > I'm quite sure it can be omitted. > > I guess it wants to preserve fields that are added in the future, > which may be useful > if the host is more recent than the guest. Good point! Thanks, //richard