Re: [Qemu-devel] [PATCHv7 0/5] block: add native support for NFS

[Peter Lieven <pl@kamp.de>]

On 29.01.2014 14:59, Stefan Hajnoczi wrote:
> On Wed, Jan 29, 2014 at 09:50:20AM +0100, Peter Lieven wrote:
>> This adds v6 of the NFS protocol driver + qemu-iotest adjustments.
>>
>> v6->v7:
>>   - removed unsused and partially non-existing libnfs header file includes [Stefan]
>>   - adjusted usage of qemu_opts_create_nofail [Stefan]
>>   - removed patch to fix output of qemu-iotest 067
>>   - only blacklist qemu-iotest 020 for NFS do not change proto from generic to file [Fam]
> It compiles now but I can't create an image on my /home NFS export:
>
> $ ./qemu-img create -f qcow2 'nfs://127.0.0.1/home/stefanha/qemu/test-nfs.img?uid=1000&gid=1000' 8G
> Formatting 'nfs://127.0.0.1/home/stefanha/qemu/test-nfs.img?uid=1000&gid=1000', fmt=qcow2 size=8589934592 encryption=off cluster_size=65536 lazy_refcounts=off
> qemu-img: nfs://127.0.0.1/home/stefanha/qemu/test-nfs.img?uid=1000&gid=1000: Failed to create file: nfs_creat_async failed
>
> I added printfs to the code, block/nfs.c is mounting /home/stefanha/qemu
> and tries to create the file /test-nfs.img.
>
> I'm using the Linux kernel NFS server.  Unfortunately I don't have more
> time to debug this but I'd like to test this feature successfully before
> merging it into QEMU.  Any ideas why libnfs refuses to create the file?
> (It's failing in nfs_lookuppath_async() with "Path is empty".)
>
> Ronnie: libnfs clobbers the nfs->rpc error string so you cannot see the
> detailed error message:
>
> In this case nfs_creat() clobbers the error with "Failed to create file:
> nfs_creat_async failed".  In fact the message was "Out of memory: failed
> to start parsing the path components" from nfs_creat_async(), but that's
> clobbering the true error too.  It really should be "Path is empty" from
> nfs_lookuppath_async().
>
> It would be nice to preserve the full error string, otherwise the user
> cannot make sense of the problem.
>
> Stefan
I do not understand why your path is empty...

Running almost the same test:

~/git/qemu$ ./qemu-img create -f qcow2 'nfs://127.0.0.1/home/lieven/git/qemu/test-nfs.img?uid=1000&gid=1000' 8G
Formatting 'nfs://127.0.0.1/home/lieven/git/qemu/test-nfs.img?uid=1000&gid=1000', fmt=qcow2 size=8589934592 encryption=off cluster_size=65536 lazy_refcounts=off
qemu-img: nfs://127.0.0.1/home/lieven/git/qemu/test-nfs.img?uid=1000&gid=1000: Failed to mount nfs share: mount/mnt call failed with "RPC error: Mount failed with error MNT3ERR_ACCES(13) Permission denied(13)"

I have to run as root or specify 'insecure' option in /etc/exports

~/git/qemu$ sudo ./qemu-img create -f qcow2 'nfs://127.0.0.1/home/lieven/git/qemu/test-nfs.img?uid=1000&gid=1000' 8G
Formatting 'nfs://127.0.0.1/home/lieven/git/qemu/test-nfs.img?uid=1000&gid=1000', fmt=qcow2 size=8589934592 encryption=off cluster_size=65536 lazy_refcounts=off

The last succeeds without problems.

Peter