Re: [libvirt] [PATCH v2 3/3] Cache result of QEMU capabilities extraction
On Mon, Mar 10, 2014 at 12:50:20PM -0600, Eric Blake wrote:
On 03/10/2014 10:54 AM, Daniel P. Berrange wrote:
> Extracting capabilities from QEMU takes a notable amount of time
> when all QEMU binaries are installed. Each system emulator
> needs about 200-300ms multiplied by 26 binaries == ~5-8 seconds.
>
> This change causes the QEMU driver to save an XML file containing
> the content of the virQEMUCaps object instance in the cache
> dir eg /var/cache/libvirt/qemu/capabilities/$SHA256(binarypath).xml
> or $HOME/.cache/libvirt/qemu/cache/capabilities/$SHA256(binarypath).xml
> + */
> +static int
> +virQEMUCapsLoadCache(virQEMUCapsPtr qemuCaps, const char *filename,
> + time_t *qemuctime, time_t *selfctime)
> +{
> + if (virXPathLongLong("string(./qemuctime)", ctxt, &l) < 0) {
> + virReportError(VIR_ERR_XML_ERROR, "%s",
> + _("missing qemuctime in QEMU capabilities XML"));
> + qemuCaps->usedQMP = virXPathBoolean("count(.//usedQMP) > 0",
Why ./qemuctime but .//usedQMP? What difference does // make in XPath?
That's a bug, but thanks to xpath it just happens to still work.
./foo means match '<foo>' as an immediate child of current node.
.//foo means match '<foo>' as an arbitrarily deep child of the
current node.
> +static int
> +virQEMUCapsSaveCache(virQEMUCapsPtr qemuCaps, const char *filename)
> +{
> + virBuffer buf = VIR_BUFFER_INITIALIZER;
> + const char *xml = NULL;
> + int ret = -1;
> + size_t i;
> +
> + virBufferAddLit(&buf, "<qemuCaps>\n");
> +
> + virBufferAsprintf(&buf, "
<qemuctime>%llu</qemuctime>\n",
Conflicts with Laine's work to require virBufferAddIndent() rather than
hard-coding indentation. Will be interesting to see who gets in first :)
Well it doesn't conflict so much as mean Laine has more work todo :-P
> +static void
> +virQEMUCapsReset(virQEMUCapsPtr qemuCaps)
> +{
> + size_t i;
> +
> + virBitmapClearAll(qemuCaps->flags);
> + qemuCaps->version = qemuCaps->kvmVersion = 0;
> + qemuCaps->arch = VIR_ARCH_NONE;
Shouldn't you also reset qemuCaps->usedQMP and qemuCaps->ctime, to get
the struct back to a known-default state? Or is this only ever going to
be used just before freeing the struct, at which point all the
reset-to-0 code is wasted CPU cycles?
It should reset usedQMP, but not ctime - the ctime value always
matches the current QEMU binary and we don't overwrite that when
loading the XML.
Regards,
Daniel
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