* [RFC][PATCH] introduce SIZE_MAX
@ 2012-04-19 4:27 Xi Wang
2012-04-20 23:03 ` Andrew Morton
0 siblings, 1 reply; 3+ messages in thread
From: Xi Wang @ 2012-04-19 4:27 UTC (permalink / raw)
To: linux-kernel
Cc: Alex Elder, Andrew Morton, David Airlie, Pekka Enberg, Xi Wang
ULONG_MAX is often used to check for integer overflow when calculating
allocation size. While ULONG_MAX happens to work on most systems,
there is no guarantee that `size_t' must be the same size as `long'.
This patch introduces SIZE_MAX, the maximum value of `size_t', to
improve portability and readability for allocation size validation.
Signed-off-by: Xi Wang <xi.wang@gmail.com>
---
This patch uses ceph and drm for demonstration purpose. I will resend
and split the patch if the new macro is found useful.
---
fs/ceph/snap.c | 2 +-
include/drm/drm_mem_util.h | 4 ++--
include/linux/kernel.h | 1 +
include/linux/slab.h | 2 +-
4 files changed, 5 insertions(+), 4 deletions(-)
diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
index f04c096..e5206fc 100644
--- a/fs/ceph/snap.c
+++ b/fs/ceph/snap.c
@@ -331,7 +331,7 @@ static int build_snap_context(struct ceph_snap_realm *realm)
/* alloc new snap context */
err = -ENOMEM;
- if (num > (ULONG_MAX - sizeof(*snapc)) / sizeof(u64))
+ if (num > (SIZE_MAX - sizeof(*snapc)) / sizeof(u64))
goto fail;
snapc = kzalloc(sizeof(*snapc) + num*sizeof(u64), GFP_NOFS);
if (!snapc)
diff --git a/include/drm/drm_mem_util.h b/include/drm/drm_mem_util.h
index 6bd325f..19a2404 100644
--- a/include/drm/drm_mem_util.h
+++ b/include/drm/drm_mem_util.h
@@ -31,7 +31,7 @@
static __inline__ void *drm_calloc_large(size_t nmemb, size_t size)
{
- if (size != 0 && nmemb > ULONG_MAX / size)
+ if (size != 0 && nmemb > SIZE_MAX / size)
return NULL;
if (size * nmemb <= PAGE_SIZE)
@@ -44,7 +44,7 @@ static __inline__ void *drm_calloc_large(size_t nmemb, size_t size)
/* Modeled after cairo's malloc_ab, it's like calloc but without the zeroing. */
static __inline__ void *drm_malloc_ab(size_t nmemb, size_t size)
{
- if (size != 0 && nmemb > ULONG_MAX / size)
+ if (size != 0 && nmemb > SIZE_MAX / size)
return NULL;
if (size * nmemb <= PAGE_SIZE)
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 645231c..b795ee5 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -35,6 +35,7 @@
#define LLONG_MAX ((long long)(~0ULL>>1))
#define LLONG_MIN (-LLONG_MAX - 1)
#define ULLONG_MAX (~0ULL)
+#define SIZE_MAX (~(size_t)0)
#define STACK_MAGIC 0xdeadbeef
diff --git a/include/linux/slab.h b/include/linux/slab.h
index a595dce..67d5d94 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -242,7 +242,7 @@ size_t ksize(const void *);
*/
static inline void *kmalloc_array(size_t n, size_t size, gfp_t flags)
{
- if (size != 0 && n > ULONG_MAX / size)
+ if (size != 0 && n > SIZE_MAX / size)
return NULL;
return __kmalloc(n * size, flags);
}
--
1.7.5.4
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [RFC][PATCH] introduce SIZE_MAX
2012-04-19 4:27 [RFC][PATCH] introduce SIZE_MAX Xi Wang
@ 2012-04-20 23:03 ` Andrew Morton
2012-04-21 2:59 ` Xi Wang
0 siblings, 1 reply; 3+ messages in thread
From: Andrew Morton @ 2012-04-20 23:03 UTC (permalink / raw)
To: Xi Wang; +Cc: linux-kernel, Alex Elder, David Airlie, Pekka Enberg
On Thu, 19 Apr 2012 00:27:51 -0400
Xi Wang <xi.wang@gmail.com> wrote:
> ULONG_MAX is often used to check for integer overflow when calculating
> allocation size. While ULONG_MAX happens to work on most systems,
> there is no guarantee that `size_t' must be the same size as `long'.
>
> This patch introduces SIZE_MAX, the maximum value of `size_t', to
> improve portability and readability for allocation size validation.
>
> ...
>
> @@ -331,7 +331,7 @@ static int build_snap_context(struct ceph_snap_realm *realm)
>
> /* alloc new snap context */
> err = -ENOMEM;
> - if (num > (ULONG_MAX - sizeof(*snapc)) / sizeof(u64))
> + if (num > (SIZE_MAX - sizeof(*snapc)) / sizeof(u64))
> goto fail;
> snapc = kzalloc(sizeof(*snapc) + num*sizeof(u64), GFP_NOFS);
> if (!snapc)
hm, yes, I suppose that's better - hardwiring the assumption that
size_t has type unsigned long is pretty ugly.
Will we need something for ssize_t also?
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [RFC][PATCH] introduce SIZE_MAX
2012-04-20 23:03 ` Andrew Morton
@ 2012-04-21 2:59 ` Xi Wang
0 siblings, 0 replies; 3+ messages in thread
From: Xi Wang @ 2012-04-21 2:59 UTC (permalink / raw)
To: Andrew Morton; +Cc: linux-kernel, Alex Elder, David Airlie, Pekka Enberg
On Apr 20, 2012, at 7:03 PM, Andrew Morton wrote:
> Will we need something for ssize_t also?
Did you mean something like SSIZE_MAX for replacing LONG_MAX? That's
a good question since we have ssize_t.
I tried to grep `LONG_MAX' and `size'. The only place I have found
so far is the following:
fs/xfs/xfs_aops.c:1247, in __xfs_get_blocks()
if (mapping_size > LONG_MAX)
mapping_size = LONG_MAX;
bh_result->b_size = mapping_size;
Not sure if SSIZE_MAX works better here (`b_size' is size_t).
- xi
^ permalink raw reply [flat|nested] 3+ messages in thread
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2012-04-19 4:27 [RFC][PATCH] introduce SIZE_MAX Xi Wang
2012-04-20 23:03 ` Andrew Morton
2012-04-21 2:59 ` Xi Wang
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