模块API之each_symbol_section

bool each_symbol_section(bool (*fn)(const struct symsearch *arr,
struct module *owner,
void *data), void *data);
函数用于在kernel中所有的symbol的区域执行fn这个函数，目前只有看到在find_symbol 这个函数中使用，用于找到对应的symbol
const struct kernel_symbol *find_symbol(const char *name,
struct module **owner,
const s32 **crc,
bool gplok,
bool warn)
{
struct find_symbol_arg fsa;

fsa.name = name;
fsa.gplok = gplok;
fsa.warn = warn;

if (each_symbol_section(find_symbol_in_section, &fsa)) {
if (owner)
*owner = fsa.owner;
if (crc)
*crc = fsa.crc;
return fsa.sym;
}

pr_debug("Failed to find symbol %s\n", name);
return NULL;
}
其源码分析如下：

bool each_symbol_section(bool (*fn)(const struct symsearch *arr,
struct module *owner,
void *data),
void *data)
{
struct module *mod;
//非模块的symbol的范围
static const struct symsearch arr[] = {
{ __start___ksymtab, __stop___ksymtab, __start___kcrctab,
NOT_GPL_ONLY, false },
{ __start___ksymtab_gpl, __stop___ksymtab_gpl,
__start___kcrctab_gpl,
GPL_ONLY, false },
{ __start___ksymtab_gpl_future, __stop___ksymtab_gpl_future,
__start___kcrctab_gpl_future,
WILL_BE_GPL_ONLY, false },
#ifdef CONFIG_UNUSED_SYMBOLS
{ __start___ksymtab_unused, __stop___ksymtab_unused,
__start___kcrctab_unused,
NOT_GPL_ONLY, true },
{ __start___ksymtab_unused_gpl, __stop___ksymtab_unused_gpl,
__start___kcrctab_unused_gpl,
GPL_ONLY, true },
#endif
};

module_assert_mutex_or_preempt();
// 首先搜索非模块的symbol
if (each_symbol_in_section(arr, ARRAY_SIZE(arr), NULL, fn, data))
return true;
//模块的symbol的范围
list_for_each_entry_rcu(mod, &modules, list) {
struct symsearch arr[] = {
{ mod->syms, mod->syms + mod->num_syms, mod->crcs,
NOT_GPL_ONLY, false },
{ mod->gpl_syms, mod->gpl_syms + mod->num_gpl_syms,
mod->gpl_crcs,
GPL_ONLY, false },
{ mod->gpl_future_syms,
mod->gpl_future_syms + mod->num_gpl_future_syms,
mod->gpl_future_crcs,
WILL_BE_GPL_ONLY, false },
#ifdef CONFIG_UNUSED_SYMBOLS
{ mod->unused_syms,
mod->unused_syms + mod->num_unused_syms,
mod->unused_crcs,
NOT_GPL_ONLY, true },
{ mod->unused_gpl_syms,
mod->unused_gpl_syms + mod->num_unused_gpl_syms,
mod->unused_gpl_crcs,
GPL_ONLY, true },
#endif
};

if (mod->state == MODULE_STATE_UNFORMED)
continue;
// 搜索模块的symbol
if (each_symbol_in_section(arr, ARRAY_SIZE(arr), mod, fn, data))
return true;
}
return false;
}
这个函数的实现可以分为两部分，kernel 中的symbol 分别模块的symbol 和 非模块的symbol，其范围分别从两个arr 数组中可以得到。再得到这两种symbol
保存的区域后调用each_symbol_in_section 在每种symbol 区域执行fn函数
static bool each_symbol_in_section(const struct symsearch *arr,
unsigned int arrsize,
struct module *owner,
bool (*fn)(const struct symsearch *syms,
struct module *owner,
void *data),
void *data)
{
unsigned int j;

for (j = 0; j < arrsize; j++) {
if (fn(&arr[j], owner, data))
return true;
}

return false;
如果fn函数返回ture，则each_symbol_section也返回ture