Michael,
It's not clear to me how this function works:
+ * Get cpu map (possible, online, etc.) address from cpu mask (since 2.6.29)
+ */
+static ulong
+get_cpu_map_addr_from_mask(const char *type)
+{
+ ulong cpu_mask_addr, cpu_map_addr;
+ char cpu_mask_symbol[32];
+ char *cpu_mask_buf;
+ int cpu_mask_size;
+
+ sprintf(cpu_mask_symbol, "cpu_%s_mask", type);
+
+ if (!symbol_exists(cpu_mask_symbol))
+ return 0;
+
+ cpu_mask_addr = symbol_value(cpu_mask_symbol);
+ cpu_mask_size = STRUCT_SIZE("cpumask");
+ cpu_mask_buf = malloc(cpu_mask_size);
+ if (!cpu_mask_buf)
+ error(FATAL, "get_cpu_map_addr_from_mask: out of memory\n");
+ readmem(cpu_mask_addr, KVADDR, cpu_mask_buf, cpu_mask_size,
+ cpu_mask_symbol, FAULT_ON_ERROR);
+ cpu_map_addr = ULONG(cpu_mask_buf + MEMBER_OFFSET("cpumask", "bits"));
+ free(cpu_mask_buf);
+
+ return cpu_map_addr;
+}
The caller to this function expects the address of a cpumask_t
data structure. As I understand it, both before and after 2.6.29,
the cpumask data structure looks like:
typedef struct cpumask {
unsigned long int bits[<variable-based-upon-NR_CPUS>];
} cpumask_t;
And pre-2.6.29, the 3 "cpu_xxxx_map" symbols were all statically
defined cpumask structures:
cpumask_t cpu_online_mask;
cpumask_t cpu_possible_mask;
cpumask_t cpu_present_mask;
Whereas now the 3 symbols don't exist except as #define's like so:
#define cpu_possible_map (*(cpumask_t *)cpu_possible_mask)
#define cpu_online_map (*(cpumask_t *)cpu_online_mask)
#define cpu_present_map (*(cpumask_t *)cpu_present_mask)
and -- if I understand the code correctly -- each cpu_xxxx_mask
is just a pointer to a cpumask data structure.
So when the caller needs the address of the relevant cpumask data structure
why doesn't your cpu_map_addr_from_mask() function simply do something
like:
get_symbol_data(cpu_mask_symbol, sizeof(void *), &tmp);
return tmp;
i.e., which would read the contents of the cpu_mask_symbol, which
is the pointer that the caller wants.
Instead, your function reads in the whole data structure, where
the cpumask.bits[] array typically contains several items, i.e.,
enough longs to contain NR_CPUS bits. Then, with ULONG(), it is
essentially reading the unsigned long value found in the first
bit[] array item, or:
cpumask.bits[0];
and therefore returning the *bitmask* contained in the first unsigned
long in the bit[] array -- instead of the *address* of the cpumask
data structure. How can that work?
Or am I missing something?
(Sorry -- I just started looking at this again, but I don't have
a test kernel of this vintage to play with...)
Dave
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