flex_array: allow 0 length elements

flex_arrays are supposed to be a replacement for:
kmalloc(num_elements * sizeof(element))

If kmalloc is given 0 num_elements or a 0 size element it will happily return
ZERO_SIZE_PTR.  Which looks like a valid allocation, but which will explode if
something actually try to use it.  The current flex_array code will return an
equivalent result if num_elements is 0, but will fail to work if
sizeof(element) is 0.  This patch allows allocation to work even for 0 size
elements.  It will cause flex_arrays to explode though if they are used.
Imitating the kmalloc behavior.

Based-on-patch-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Eric Paris <eparis@redhat.com>
Acked-by: Dave Hansen <dave@linux.vnet.ibm.com>

diff --git a/lib/flex_array.c b/lib/flex_array.c
index 854b57b..cab7621 100644 (file)
--- a/lib/flex_array.c
+++ b/lib/flex_array.c
@@ -88,8 +88,11 @@ struct flex_array *flex_array_alloc(int element_size, unsigned int total,
                                        gfp_t flags)
 {
        struct flex_array *ret;
-       int max_size = FLEX_ARRAY_NR_BASE_PTRS *
-                               FLEX_ARRAY_ELEMENTS_PER_PART(element_size);
+       int max_size = 0;
+
+       if (element_size)
+               max_size = FLEX_ARRAY_NR_BASE_PTRS *
+                          FLEX_ARRAY_ELEMENTS_PER_PART(element_size);
 
        /* max_size will end up 0 if element_size > PAGE_SIZE */
        if (total > max_size)
@@ -183,15 +186,18 @@ __fa_get_part(struct flex_array *fa, int part_nr, gfp_t flags)
 int flex_array_put(struct flex_array *fa, unsigned int element_nr, void *src,
                        gfp_t flags)
 {
-       int part_nr = fa_element_to_part_nr(fa, element_nr);
+       int part_nr;
        struct flex_array_part *part;
        void *dst;
 
        if (element_nr >= fa->total_nr_elements)
                return -ENOSPC;
+       if (!fa->element_size)
+               return 0;
        if (elements_fit_in_base(fa))
                part = (struct flex_array_part *)&fa->parts[0];
        else {
+               part_nr = fa_element_to_part_nr(fa, element_nr);
                part = __fa_get_part(fa, part_nr, flags);
                if (!part)
                        return -ENOMEM;
@@ -211,15 +217,18 @@ EXPORT_SYMBOL(flex_array_put);
  */
 int flex_array_clear(struct flex_array *fa, unsigned int element_nr)
 {
-       int part_nr = fa_element_to_part_nr(fa, element_nr);
+       int part_nr;
        struct flex_array_part *part;
        void *dst;
 
        if (element_nr >= fa->total_nr_elements)
                return -ENOSPC;
+       if (!fa->element_size)
+               return 0;
        if (elements_fit_in_base(fa))
                part = (struct flex_array_part *)&fa->parts[0];
        else {
+               part_nr = fa_element_to_part_nr(fa, element_nr);
                part = fa->parts[part_nr];
                if (!part)
                        return -EINVAL;
@@ -264,6 +273,8 @@ int flex_array_prealloc(struct flex_array *fa, unsigned int start,
 
        if (end >= fa->total_nr_elements)
                return -ENOSPC;
+       if (!fa->element_size)
+               return 0;
        if (elements_fit_in_base(fa))
                return 0;
        start_part = fa_element_to_part_nr(fa, start);
@@ -291,14 +302,17 @@ EXPORT_SYMBOL(flex_array_prealloc);
  */
 void *flex_array_get(struct flex_array *fa, unsigned int element_nr)
 {
-       int part_nr = fa_element_to_part_nr(fa, element_nr);
+       int part_nr;
        struct flex_array_part *part;
 
+       if (!fa->element_size)
+               return NULL;
        if (element_nr >= fa->total_nr_elements)
                return NULL;
        if (elements_fit_in_base(fa))
                part = (struct flex_array_part *)&fa->parts[0];
        else {
+               part_nr = fa_element_to_part_nr(fa, element_nr);
                part = fa->parts[part_nr];
                if (!part)
                        return NULL;
@@ -353,7 +367,7 @@ int flex_array_shrink(struct flex_array *fa)
        int part_nr;
        int ret = 0;
 
-       if (!fa->total_nr_elements)
+       if (!fa->total_nr_elements || !fa->element_size)
                return 0;
        if (elements_fit_in_base(fa))
                return ret;