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 <rjo...@redhat.com> > 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 <jc...@redhat.com>