Re: [Qemu-devel] [PATCH] block/raw-posix: Open file descriptor O_RDWR to work around glibc posix_fallocate emulation issue.

[Richard W.M. Jones]

On Fri, Oct 02, 2015 at 03:36:04PM +0100, Peter Maydell wrote:
> On 29 September 2015 at 16:54, Richard W.M. Jones <address@hidden> 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
> 
> "You are not authorized to access bug #1265196."
> 
> Any chance of a working URL if we're going to immortalize it
> in QEMU's git log?

Sorry about that.  I have now made the bug public -- there was
absolutely no reason why it was private before.

Rich.

-- 
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