Re: [Qemu-devel] [PATCH] Raise 9pfs mount_tag limit from 32 to 255 bytes

[Aneesh Kumar K.V]

On Thu, 29 Sep 2011 11:34:21 +0100, "Daniel P. Berrange" <address@hidden> wrote:
> From: "Daniel P. Berrange" <address@hidden>
> 
> The Linux guest kernel does not appear to have a problem handling
> a mount_tag larger than 32 bytes. Increase the limit to 255 bytes,
> though perhaps it can be made larger still, or not limited at all ?
> 
> Tested with a 3.0.4 kernel and a mount_tag 255 bytes in length.
> 
> * hw/9pfs/virtio-9p.h: Change MAX_TAG_LEN to 255


mount_tag is passed via pci config space, do we want to have 255 bytes
out of that for device identification. Is this change driven by 
the virt-manager UI where we specify source and target directory for
file system ?. I would like to understand how that target
directory is used in case of other user like NFS ?. If this is something
used to get automout (I am not sure how we drive such an automount) of
those mounts points, then it should be ok for VirtFS to generate mount tag 
internally
which will fit 32 byte limit and use the target directory for
automounting the mount point using the internally generated mount tag


> 
> Signed-off-by: Daniel P. Berrange <address@hidden>
> ---
>  hw/9pfs/virtio-9p.h |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/hw/9pfs/virtio-9p.h b/hw/9pfs/virtio-9p.h
> index 17d44b4..b133b33 100644
> --- a/hw/9pfs/virtio-9p.h
> +++ b/hw/9pfs/virtio-9p.h
> @@ -144,7 +144,7 @@ struct V9fsPDU
>  /* The ID for virtio console */
>  #define VIRTIO_ID_9P    9
>  #define MAX_REQ         128
> -#define MAX_TAG_LEN     32
> +#define MAX_TAG_LEN     255
> 
>  #define BUG_ON(cond) assert(!(cond))
> 

-aneesh