From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:60509) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZhOF9-0002Dc-Tj for qemu-devel@nongnu.org; Wed, 30 Sep 2015 16:44:52 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZhOF8-0001el-UK for qemu-devel@nongnu.org; Wed, 30 Sep 2015 16:44:51 -0400 Date: Wed, 30 Sep 2015 16:44:42 -0400 From: Jeff Cody Message-ID: <20150930204442.GF29557@localhost.localdomain> References: <1443542050-26720-1-git-send-email-rjones@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1443542050-26720-1-git-send-email-rjones@redhat.com> Subject: Re: [Qemu-devel] [Qemu-block] [PATCH] block/raw-posix: Open file descriptor O_RDWR to work around glibc posix_fallocate emulation issue. List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Richard W.M. Jones" Cc: kwolf@redhat.com, codonell@redhat.com, dgilbert@redhat.com, qemu-block@nongnu.org, qemu-devel@nongnu.org On Tue, Sep 29, 2015 at 04:54:10PM +0100, Richard W.M. Jones wrote: > https://bugzilla.redhat.com/show_bug.cgi?id=1265196 > > The following command fails on an NFS mountpoint: > > $ qemu-img create -f qcow2 -o preallocation=falloc disk.img 262144 > Formatting 'disk.img', fmt=qcow2 size=262144 encryption=off cluster_size=65536 preallocation='falloc' lazy_refcounts=off > qemu-img: disk.img: Could not preallocate data for the new file: Bad file descriptor > > The reason turns out to be because NFS doesn't support the > posix_fallocate call. glibc emulates it instead. However glibc's > emulation involves using the pread(2) syscall. The pread syscall > fails with EBADF if the file descriptor is opened without the read > open-flag (ie. open (..., O_WRONLY)). > > I contacted glibc upstream about this, and their response is here: > > https://bugzilla.redhat.com/show_bug.cgi?id=1265196#c9 > > There are two possible fixes: Use Linux fallocate directly, or (this > fix) work around the problem in qemu by opening the file with O_RDWR > instead of O_WRONLY. > > Signed-off-by: Richard W.M. Jones > BZ: https://bugzilla.redhat.com/show_bug.cgi?id=1265196 > --- > block/raw-posix.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/block/raw-posix.c b/block/raw-posix.c > index 30df8ad..86f8562 100644 > --- a/block/raw-posix.c > +++ b/block/raw-posix.c > @@ -1648,7 +1648,7 @@ static int raw_create(const char *filename, QemuOpts *opts, Error **errp) > goto out; > } > > - fd = qemu_open(filename, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY, > + fd = qemu_open(filename, O_RDWR | O_CREAT | O_TRUNC | O_BINARY, > 0644); > if (fd < 0) { > result = -errno; > -- > 2.5.0 > > Reviewed-by: Jeff Cody