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cache: scan kallsyms for kernel symbols

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With monolithic kernels we can't actually modprobe
for cache modules as they are already compiled-in
and policy modules do not export version symbol.

Reported issue on list:
https://www.redhat.com/archives/dm-devel/2017-March/msg00061.html

Fix will try to look for explicit kernel symbols first before
calling modprobe.
This commit is contained in:
Zdenek Kabelac 2017-03-31 17:07:21 +02:00
parent 13ca11cc14
commit 970df59f91
1 changed files with 40 additions and 5 deletions
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45
lib/cache_segtype/cache.c
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@ -258,6 +258,39 @@ static void _destroy(struct segment_type *segtype)
}
#ifdef DEVMAPPER_SUPPORT
/*
* Parse and look for kernel symbol in /proc/kallsyms
* this could be our only change to figure out there is
* cache policy symbol already in the monolithic kernel
* where 'modprobe dm-cache-smq' will simply not work
*/
static int _lookup_kallsyms(const char *symbol)
{
static const char _syms[] = "/proc/kallsyms";
int ret = 0;
char *line = NULL;
size_t len;
FILE *s;
if (!(s = fopen(_syms, "r")))
log_sys_debug("fopen", _syms);
else {
while (getline(&line, &len, s) != -1)
if (strstr(line, symbol)) {
ret = 1; /* Found symbol */
log_debug("Found kernel symbol%s.", symbol); /* space is in symbol */
break;
}
free(line);
if (fclose(s))
log_sys_debug("fclose", _syms);
}
return ret;
}
static int _target_present(struct cmd_context *cmd,
const struct lv_segment *seg __attribute__((unused)),
unsigned *attributes __attribute__((unused)))
@ -270,14 +303,15 @@ static int _target_present(struct cmd_context *cmd,
unsigned cache_alias;
const char feature[12];
const char module[12]; /* check dm-%s */
const char ksymbol[12]; /* check for kernel symbol */
const char *aliasing;
} _features[] = {
/* Assumption: cache >=1.9 always aliases MQ policy */
{ 1, 10, CACHE_FEATURE_METADATA2, 0, "metadata2" },
/* Assumption: cache >=1.9 always aliases MQ policy */
{ 1, 9, CACHE_FEATURE_POLICY_SMQ, CACHE_FEATURE_POLICY_MQ, "policy_smq", "cache-smq",
" and aliases cache-mq" },
{ 1, 8, CACHE_FEATURE_POLICY_SMQ, 0, "policy_smq", "cache-smq" },
{ 1, 3, CACHE_FEATURE_POLICY_MQ, 0, "policy_mq", "cache-mq" },
" smq_exit", " and aliases cache-mq" },
{ 1, 8, CACHE_FEATURE_POLICY_SMQ, 0, "policy_smq", "cache-smq", " smq_exit" },
{ 1, 3, CACHE_FEATURE_POLICY_MQ, 0, "policy_mq", "cache-mq", " mq_init" },
};
static const char _lvmconf[] = "global/cache_disabled_features";
static unsigned _attrs = 0;
@ -323,7 +357,8 @@ static int _target_present(struct cmd_context *cmd,
}
if (((maj > _features[i].maj) ||
(maj == _features[i].maj && min >= _features[i].min)) &&
module_present(cmd, _features[i].module)) {
((_features[i].ksymbol[0] && _lookup_kallsyms(_features[i].ksymbol)) ||
module_present(cmd, _features[i].module))) {
log_debug_activation("Cache policy %s is available%s.",
_features[i].module,
_features[i].aliasing ? : "");