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From: | Anthony Liguori |
Subject: | Re: [Qemu-devel] [PATCH] Raise 9pfs mount_tag limit from 32 to 255 bytes |
Date: | Tue, 01 Nov 2011 13:27:56 -0500 |
User-agent: | Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.21) Gecko/20110831 Lightning/1.0b2 Thunderbird/3.1.13 |
On 10/20/2011 10:13 AM, Daniel P. Berrange wrote:
On Fri, Oct 07, 2011 at 04:49:13PM +0530, Aneesh Kumar K.V wrote:On Fri, 7 Oct 2011 10:27:56 +0100, "Daniel P. Berrange"<address@hidden> wrote:On Thu, Sep 29, 2011 at 04:22:16PM +0100, Daniel P. Berrange wrote:On Thu, Sep 29, 2011 at 08:23:49PM +0530, Aneesh Kumar K.V wrote: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 255mount_tag is passed via pci config space, do we want to have 255 bytes out of that for device identification.How big is the config space available for each 9pfs device and what other info does it need to keep there ?Does anyone have an clear answer for this ? I've done some tests with ever larger mount tags, and managed to increase the MAX_TAG_LEN value to 1023 before I started getting guest failures. So if the config space is really 1023 bytes in size, it doesn't seem too unrealistic to allow 255 bytes of it for the mount_tag, or at the very least increase it from 32 to 128 ?Last time we discussed this Anthony wanted to keep the config space usage minimal, hence we agreed on the size 32 bytes.Ping ? Anyone .... Does anyone have any clear information about the per-device config space we have available ? As above I'd really like us to raise the mount_tag length even just a little bit higher for QEMU 1.0, if we have the PCI config space available to play with.
Yes, PCI PIO space is very small. I think 128 is even pushing it.Why not add a feature that exchanges the tag through another mechanism such that there doesn't need to be a limit? It could be as simple as adding an fsstat .L operation or something like that.
Regards, Anthony Liguori
Regards, Daniel
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