[libvirt] [PATCHv3 1/4] nodeinfo: enable nodeGetCPUCount for older kernels

[Eric Blake]

On 11/13/2012 05:54 AM, Viktor Mihajlovski wrote:
> Since /sys/devices/system/cpu/present is not available on
> older kernels like on RHEL 5.x nodeGetCPUCount will
> fail there. The fallback implemented is to scan for
> /sys/devices/system/cpu/cpuNN entries.
> 
> Signed-off-by: Viktor Mihajlovski <mihajlov at linux.vnet.ibm.com>
> ---
>  src/nodeinfo.c | 33 ++++++++++++++++++++++++++++-----
>  1 file changed, 28 insertions(+), 5 deletions(-)

>  #ifdef __linux__
> -    /* XXX should we also work on older kernels, like RHEL5, that lack
> -     * cpu/present and cpu/online files?  Those kernels also lack cpu
> -     * hotplugging, so it would be a matter of finding the largest
> -     * cpu/cpuNN directory, and returning NN + 1 */
> -    return linuxParseCPUmax(SYSFS_SYSTEM_PATH "/cpu/present");
> +    /* to support older kernels, like RHEL5, that lack
> +     * cpu/present we fall back to count cpu/cpuNN
> +     * entries.
> +     */
> +    char *cpupath = NULL;
> +    int i = 0;
> +
> +    if (virFileExists(SYSFS_SYSTEM_PATH "/cpu/present")) {
> +        i = linuxParseCPUmax(SYSFS_SYSTEM_PATH "/cpu/present");
> +    } else if (virFileExists(SYSFS_SYSTEM_PATH "/cpu/cpu0")) {
> +        do {
> +            i++;
> +            VIR_FREE(cpupath);
> +            if (virAsprintf(&cpupath, "%s/cpu/cpu%d",
> +                            SYSFS_SYSTEM_PATH, i) < 0) {
> +                virReportOOMError();
> +                return -1;
> +            }
> +        } while (virFileExists(cpupath));

The assumption here is that any kernel lacking cpu/present also lacks
hotplug, and therefore the cpuNN will be consecutive and we aren't going
to miss anything.  You removed that assumption from the comment, but I
think it is important to leave in.

ACK.  I'm firing up my RHEL 5 VM to test this before I push with this
comment change, but it looks sane.

diff --git i/src/nodeinfo.c w/src/nodeinfo.c
index cea3775..4589b77 100644
--- i/src/nodeinfo.c
+++ w/src/nodeinfo.c
@@ -978,9 +978,10 @@ int
 nodeGetCPUCount(void)
 {
 #ifdef __linux__
-    /* to support older kernels, like RHEL5, that lack
-     * cpu/present we fall back to count cpu/cpuNN
-     * entries.
+    /* To support older kernels that lack cpu/present, such as 2.6.18
+     * in RHEL5, we fall back to count cpu/cpuNN entries; this assumes
+     * that such kernels also lack hotplug, and therefore cpu/cpuNN
+     * will be consecutive.
      */
     char *cpupath = NULL;
     int i = 0;


-- 
Eric Blake   eblake at redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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