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resolv: Introduce free list for resolv_conf index slosts

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This commit is contained in:
Florian Weimer
2017-07-03 15:01:34 +02:00
parent aef16cc8a4
commit e237357a5a
4 changed files with 142 additions and 32 deletions
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71
resolv/resolv_conf.c
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@ -28,9 +28,12 @@
struct resolv_conf_array object. The intent of this construction
is to make reasonably sure that even if struct __res_state objects
are copied around and patched by applications, we can still detect
accesses to stale extended resolver state. */
accesses to stale extended resolver state. The array elements are
either struct resolv_conf * pointers (if the LSB is cleared) or
free list entries (if the LSB is set). The free list is used to
speed up finding available entries in the array. */
#define DYNARRAY_STRUCT resolv_conf_array
#define DYNARRAY_ELEMENT struct resolv_conf *
#define DYNARRAY_ELEMENT uintptr_t
#define DYNARRAY_PREFIX resolv_conf_array_
#define DYNARRAY_INITIAL_SIZE 0
#include <malloc/dynarray-skeleton.c>
@ -55,6 +58,10 @@ struct resolv_conf_global
the array element is overwritten with NULL. */
struct resolv_conf_array array;
/* Start of the free list in the array. The MSB is set if this
field has been initialized. */
uintptr_t free_list_start;
/* Cached current configuration object for /etc/resolv.conf. */
struct resolv_conf *conf_current;
@ -194,15 +201,17 @@ resolv_conf_get_1 (const struct __res_state *resp)
contexts exists, so returning NULL is correct. */
return NULL;
size_t index = resp->_u._ext.__glibc_extension_index ^ INDEX_MAGIC;
struct resolv_conf *conf;
struct resolv_conf *conf = NULL;
if (index < resolv_conf_array_size (&global_copy->array))
{
conf = *resolv_conf_array_at (&global_copy->array, index);
assert (conf->__refcount > 0);
++conf->__refcount;
uintptr_t *slot = resolv_conf_array_at (&global_copy->array, index);
if (!(*slot & 1))
{
conf = (struct resolv_conf *) *slot;
assert (conf->__refcount > 0);
++conf->__refcount;
}
}
else
conf = NULL;
put_locked_global (global_copy);
return conf;
}
@ -550,17 +559,20 @@ decrement_at_index (struct resolv_conf_global *global_copy, size_t index)
{
if (index < resolv_conf_array_size (&global_copy->array))
{
/* Index found. Deallocate the struct resolv_conf object once
the reference counter reaches. Free the array slot. */
struct resolv_conf **slot
= resolv_conf_array_at (&global_copy->array, index);
struct resolv_conf *conf = *slot;
if (conf != NULL)
/* Index found. */
uintptr_t *slot = resolv_conf_array_at (&global_copy->array, index);
/* Check that the slot is not already part of the free list. */
if (!(*slot & 1))
{
struct resolv_conf *conf = (struct resolv_conf *) *slot;
conf_decrement (conf);
/* Clear the slot even if the reference count is positive.
Slots are not shared. */
*slot = NULL;
/* Put the slot onto the free list. */
if (global_copy->free_list_start == 0)
/* Not yet initialized. */
*slot = 1;
else
*slot = global_copy->free_list_start;
global_copy->free_list_start = (index << 1) | 1;
}
}
}
@ -580,24 +592,21 @@ __resolv_conf_attach (struct __res_state *resp, struct resolv_conf *conf)
/* Try to find an unused index in the array. */
size_t index;
{
size_t size = resolv_conf_array_size (&global_copy->array);
bool found = false;
for (index = 0; index < size; ++index)
if (global_copy->free_list_start & 1)
{
struct resolv_conf **p
= resolv_conf_array_at (&global_copy->array, index);
if (*p == NULL)
{
*p = conf;
found = true;
break;
}
/* Unlink from the free list. */
index = global_copy->free_list_start >> 1;
uintptr_t *slot = resolv_conf_array_at (&global_copy->array, index);
global_copy->free_list_start = *slot;
assert (global_copy->free_list_start & 1);
/* Install the configuration pointer. */
*slot = (uintptr_t) conf;
}
if (!found)
else
{
size_t size = resolv_conf_array_size (&global_copy->array);
/* No usable index found. Increase the array size. */
resolv_conf_array_add (&global_copy->array, conf);
resolv_conf_array_add (&global_copy->array, (uintptr_t) conf);
if (resolv_conf_array_has_failed (&global_copy->array))
{
put_locked_global (global_copy);