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Re: [Qemu-devel] [PATCH] block/raw-posix: Open file descriptor O_RDWR to
From: |
Peter Maydell |
Subject: |
Re: [Qemu-devel] [PATCH] block/raw-posix: Open file descriptor O_RDWR to work around glibc posix_fallocate emulation issue. |
Date: |
Fri, 2 Oct 2015 15:36:04 +0100 |
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?
thanks
-- PMM