Re: [libvirt] [PATCH v2] domain: fix parsing of memory tunables on 32-bit machines

Commit 6c9a8a4 (Oct 2014) exposed a long-standing issue on 32-bit machines: code related to virDomainSetMemoryParameters has always been documented as using a 64-bit limit, but it was implemented by calling virDomainParseMemory which enforced an 'unsigned long' limit. Since VIR_DOMAIN_MEMORY_PARAM_UNLIMITED capped to a long is -1, but virDomainParseScaledValue no longer accepts negative values, an attempt to use 2^53-1 as a hard memory limit started failing the testsuite. However, the problem with capping things artificially low has existed for much longer - ever since commits 4888f0fb and 2e22f23 (Mar 2012) switched internal tracking from 'unsigned long' to 'unsigned long long' (prior to that time, the cap was a side-effect of the choice of types). We _have_ to cap the balloon memory values, (no thanks to baked in 'unsigned long' of API such as virDomainSetMaxMemory or virDomainGetInfo with no

counterpart API that guarantees 64-bit access to those numbers) but memory parameters have never needed the artificial limit. At any rate, the solution is to make the parser function gain a parameter, and only do the reduced 32-bit cap for the values that are constrained due to API. * src/conf/domain_conf.h (_virDomainMemtune): Add comments. * src/conf/domain_conf.c (virDomainParseMemory): Add parameter. (virDomainDefParseXML): Adjust callers. Signed-off-by: Eric Blake <eblake(a)redhat.com&gt; --- src/conf/domain_conf.c | 25 ++++++++++++++----------- src/conf/domain_conf.h | 14 ++++++++------ 2 files changed, 22 insertions(+), 17 deletions(-) diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c index 39befb0..c594325 100644 --- a/src/conf/domain_conf.c +++ b/src/conf/domain_conf.c @@ -6373,19 +6373,22 @@ virDomainParseScaledValue(const char *xpath, /* Parse a memory element located at XPATH within CTXT, and store the - * result into MEM. If REQUIRED, then the value must exist; - * otherwise, the value is optional. The value is in blocks of 1024. - * Return 0 on success, -1 on failure after issuing error. */ + * result into MEM, in blocks of 1024. If REQUIRED, then the value + * must exist; otherwise, the value is optional. The value must not + * exceed VIR_DOMAIN_MEMORY_PARAM_UNLIMITED once scaled; additionally, + * if CAPPED is true, the value must fit within an unsigned long (only + * matters on 32-bit platforms). Return 0 on success, -1 on failure + * after issuing error. */