[libvirt] [PATCH] Allow for URI aliases when connecting to libvirt

[Eric Blake]

On 10/13/2011 04:53 AM, Daniel P. Berrange wrote:
> From: "Daniel P. Berrange"<berrange at redhat.com>
>
> I finally got fed up of typing URIs when using virsh....
>
> This adds support for a libvirt client configuration file
> either /etc/libvirt/libvirt.conf for privileged clients,
> or $HOME/.libvirt/libvirt.conf for unprivileged clients.

Cool idea!

Potential problem - our testsuite uses -c test:///default (or similar); 
there's a case where we _don't_ want to use alias lookup.  But I guess 
if valid alias names cannot contain ':', then the presence of ':' in the 
target name is sufficient to prove that we don't want to use aliases. 
[This is a review as I go reply, so I'll see what the code actually does...]

> +<h2>
> +<a name="URI_config">Configuring URI aliases</a>
> +</h2>
> +
> +<p>
> +To simplify live for administrators, it is possible to setup URI aliases in a

s/live/life/

> +libvirt client configuration file. The configuration file is<code>/etc/libvirt/libvirt.conf</code>
> +for the root user, or<code>$HOME/.libvirt/libvirt.conf</code>  for any unprivileged user.

Really?  Shouldn't it instead be that /etc is for qemu:///system, and 
$HOME/.libvirt is for any user, _including root_, for qemu:///session.

> +<p>
> +  A URI alias should be a string made up from the characters
> +<code>a-Z, 0-9, _, -</code>. Following the<code>=</code>
> +  can be any libvirt URI string, including arbitrary URI parameters.
> +  URI aliases will apply to any application opening a libvirt
> +  connection, unless it has explicitly passed the<code>VIR_CONNECT_NO_ALIASES</code>
> +  parameter to<code>virConnectOpenAuth</code>.

Should we document that aliases are not consulted if the non-NULL 
connection name includes ':'?

> +++ b/include/libvirt/libvirt.h.in
> @@ -843,7 +843,8 @@ typedef virNodeMemoryStats *virNodeMemoryStatsPtr;
>    * Flags when opening a connection to a hypervisor
>    */
>   typedef enum {
> -    VIR_CONNECT_RO = 1,    /* A readonly connection */
> +    VIR_CONNECT_RO         = (1<<  0),  /* A readonly connection */
> +    VIR_CONNECT_NO_ALIASES = (1<<  1),  /* Don't try to resolve URI aliases */

At first glance, I didn't see a use for this bit: it seems like the 
decision to use aliases is unambiguous - if the name contains ':', there 
is no alias, and if it lacks ':', then the only way it can succeed is if 
an alias lookup is successful.  Oh, I see - you use 
VIR_CONNECT_NO_ALIASES to force failure rather than attempt an alias 
lookup for the case where name has no ':'.  Okay, it makes sense.

>   }
>
> +static char *
> +virConnectConfigFile(void)
> +{
> +    char *path;
> +    if (geteuid() == 0) {
> +        if (virAsprintf(&path, "%s/libvirt/libvirt.conf",
> +                        SYSCONFDIR)<  0)
> +            goto no_memory;

Hmm, while I asked above whether qemu:///session for root should use 
~root/.libvirt, the code matches your documentation.  So if you like my 
idea, then this needs a tweak (probably pass in a parameter for whether 
the connection itself is system vs. session).

> +static int
> +virConnectOpenFindURIAliasMatch(virConfValuePtr value, const char *alias, char **uri)
> +{
> +    virConfValuePtr entry;
> +    if (value->type != VIR_CONF_LIST) {
> +        virLibConnError(VIR_ERR_INTERNAL_ERROR, "%s",

Fair enough - only a coding error would trigger this error.

> +                        _("Expected a list for 'uri_aliases' config parameter"));
> +        return -1;
> +    }
> +
> +    entry = value->list;
> +    while (entry) {
> +        char *offset;
> +        size_t safe;
> +
> +        if (entry->type != VIR_CONF_STRING) {
> +            virLibConnError(VIR_ERR_INTERNAL_ERROR, "%s",

Wouldn't VIR_ERR_CONF_SYNTAX go better here?

> +                            _("Expected a string for 'uri_aliases' config parameter list entry"));
> +            return -1;
> +        }
> +
> +        if (!(offset = strchr(entry->str, '='))) {
> +            virLibConnError(VIR_ERR_INTERNAL_ERROR,

and here

> +                            _("Malformed 'uri_aliases' config entry '%s', expected 'alias=uri://host/path'"),
> +                            entry->str);
> +            return -1;
> +        }
> +
> +        safe  = strspn(entry->str, "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789_-");
> +        if (safe<  (offset - entry->str)) {
> +            virLibConnError(VIR_ERR_INTERNAL_ERROR,

and here

> +static int
> +virConnectOpenResolveURIAlias(const char *alias, char **uri)
> +{
> +    char *config = NULL;
> +    int ret = -1;
> +    virConfPtr conf = NULL;
> +    virConfValuePtr value = NULL;
> +
> +    *uri = NULL;
> +
> +    /* Short circuit to avoid doing URI alias resolution
> +     * when it clearly isn't an alias */
> +    if (strchr(alias, '/') ||
> +        strchr(alias, ':'))
> +        return 0;

Aha, I was right - no alias lookup on full URIs.

> diff --git a/src/libvirt.conf b/src/libvirt.conf
> new file mode 100644
> index 0000000..ffe8c21
> --- /dev/null
> +++ b/src/libvirt.conf
> @@ -0,0 +1,13 @@
> +

Why a leading blank line?

ACK with nits fixed.

-- 
Eric Blake   eblake at redhat.com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org