Re: [Qemu-trivial] [Qemu-devel] [PATCH] nbd: fix trim/discard commands with a length bigger than NBD_MAX_BUFFER_SIZE

[Quentin Casasnovas <quentin.casasnovas@oracle.com>]

On Tue, May 10, 2016 at 02:34:18PM -0600, Eric Blake wrote:
> On 05/06/2016 02:45 AM, Quentin Casasnovas wrote:
> > When running fstrim on a filesystem mounted through qemu-nbd with
> > --discard=on, fstrim would fail with I/O errors:
> > 
> >   $ fstrim /k/spl/ice/
> >   fstrim: /k/spl/ice/: FITRIM ioctl failed: Input/output error
> > 
> > and qemu-nbd was spitting these:
> > 
> >   nbd.c:nbd_co_receive_request():L1232: len (94621696) is larger than max len (33554432)
> 
> Your patch duplicates what is already present in qemu:
> 
> commit eb38c3b67018ff8069e4f674a28661931a8a3e4f
> Author: Paolo Bonzini <pbonzini@redhat.com>
> Date:   Thu Jan 7 14:32:42 2016 +0100
> 
>     nbd-server: do not check request length except for reads and writes
> 
>     Only reads and writes need to allocate memory correspondent to the
>     request length.  Other requests can be sent to the storage without
>     allocating any memory, and thus any request length is acceptable.
> 
>     Reported-by: Sitsofe Wheeler <sitsofe@yahoo.com>
>     Cc: qemu-block@nongnu.org
>     Reviewed-by: Max Reitz <mreitz@redhat.com>
>     Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> 
> For the purposes of qemu-stable, it's better to backport the existing
> patch than to write a new version of it.
> 

Ha sorry I missed this! I wouldn't have tried to debug/fix myself otherwise :)

> It also helps to state what version of qemu you were testing, as it is
> obviously not the (soon-to-be-released) version 2.6 which already has
> the fix.
>

I was using qemu-2.5.0-rc3 on Gentoo but this was also verified on some
Debian systems which appears to be on 1.1.2+dfsg-6a+deb7u12 and on Ubuntu
Xenial 2.0.0+dfsg-2ubuntu1.22.

I wrote the patch on top of https://github.com/bonzini/qemu.git:master
(a7e00e2) which didn't contain the fix last Friday.

Anyway, cool if the fix is going into mainline :)

Quentin