[libvirt] [PATCH 1/4] memory: make it safer to expand arrays
Eric Blake
eblake at redhat.com
Sat Aug 14 16:23:53 UTC 2010
Note - I did _not_ update HACKING. Do we have a makefile rule
for doing an auto-xsl translation from hacking.html.in yet, or
is something I'll have to do manually before pushing this?
* src/util/memory.h (VIR_REALLOC_N): Update docs.
(VIR_EXPAND_N, VIR_SHRINK_N): New macros.
(virAlloc, virAllocN, virReallocN, virAllocVar, virFree): Add some
gcc attributes.
* src/util/memory.c (virExpandN, virShrinkN): New functions.
(virReallocN): Update docs.
* docs/hacking.html.in: Prefer newer interfaces over
VIR_REALLOC_N, since uninitialized memory can bite us.
---
docs/hacking.html.in | 24 +++++++++++--------
src/util/memory.c | 59 +++++++++++++++++++++++++++++++++++++++++++++++++-
src/util/memory.h | 51 ++++++++++++++++++++++++++++++++++++++-----
3 files changed, 117 insertions(+), 17 deletions(-)
diff --git a/docs/hacking.html.in b/docs/hacking.html.in
index deab530..4cc92f4 100644
--- a/docs/hacking.html.in
+++ b/docs/hacking.html.in
@@ -332,11 +332,11 @@
Use of the malloc/free/realloc/calloc APIs is deprecated in the libvirt
codebase, because they encourage a number of serious coding bugs and do
not enable compile time verification of checks for NULL. Instead of these
- routines, use the macros from memory.h
+ routines, use the macros from memory.h.
</p>
<ul>
- <li><p>eg to allocate a single object:</p>
+ <li><p>To allocate a single object:</p>
<pre>
virDomainPtr domain;
@@ -347,11 +347,11 @@
}
</pre></li>
- <li><p>eg to allocate an array of objects</p>
+ <li><p>To allocate an array of objects</p>
<pre>
virDomainPtr domains;
- int ndomains = 10;
+ size_t ndomains = 10;
if (VIR_ALLOC_N(domains, ndomains) < 0) {
virReportOOMError();
@@ -359,7 +359,7 @@
}
</pre></li>
- <li><p>eg to allocate an array of object pointers</p>
+ <li><p>To allocate an array of object pointers</p>
<pre>
virDomainPtr *domains;
@@ -371,18 +371,22 @@
}
</pre></li>
- <li><p>eg to re-allocate the array of domains to be longer</p>
+ <li><p>To re-allocate the array of domains to be 10 elements longer</p>
<pre>
- ndomains = 20
-
- if (VIR_REALLOC_N(domains, ndomains) < 0) {
+ if (VIR_EXPAND_N(domains, ndomains, 10) < 0) {
virReportOOMError();
return NULL;
}
</pre></li>
- <li><p>eg to free the domain</p>
+ <li><p>To trim an array of domains to have one less element</p>
+
+<pre>
+ VIR_SHRINK_N(domains, ndomains, 1);
+</pre></li>
+
+ <li><p>To free the domain</p>
<pre>
VIR_FREE(domain);
diff --git a/src/util/memory.c b/src/util/memory.c
index dd1216b..e95aa47 100644
--- a/src/util/memory.c
+++ b/src/util/memory.c
@@ -1,6 +1,7 @@
/*
* memory.c: safer memory allocation
*
+ * Copyright (C) 2010 Red Hat, Inc.
* Copyright (C) 2008 Daniel P. Berrange
*
* This library is free software; you can redistribute it and/or
@@ -24,6 +25,7 @@
#include <stddef.h>
#include "memory.h"
+#include "ignore-value.h"
#if TEST_OOM
@@ -141,7 +143,7 @@ int virAllocN(void *ptrptr, size_t size, size_t count)
* 'count' elements, each 'size' bytes in length. Update 'ptrptr'
* with the address of the newly allocated memory. On failure,
* 'ptrptr' is not changed and still points to the original memory
- * block. The newly allocated memory is filled with zeros.
+ * block. Any newly allocated memory in 'ptrptr' is uninitialized.
*
* Returns -1 on failure to allocate, zero on success
*/
@@ -165,6 +167,61 @@ int virReallocN(void *ptrptr, size_t size, size_t count)
}
/**
+ * virExpandN:
+ * @ptrptr: pointer to pointer for address of allocated memory
+ * @size: number of bytes per element
+ * @countptr: pointer to number of elements in array
+ * @add: number of elements to add
+ *
+ * Resize the block of memory in 'ptrptr' to be an array of
+ * '*countptr' + 'add' elements, each 'size' bytes in length.
+ * Update 'ptrptr' and 'countptr' with the details of the newly
+ * allocated memory. On failure, 'ptrptr' and 'countptr' are not
+ * changed. Any newly allocated memory in 'ptrptr' is zero-filled.
+ *
+ * Returns -1 on failure to allocate, zero on success
+ */
+int virExpandN(void *ptrptr, size_t size, size_t *countptr, size_t add)
+{
+ int res;
+
+ if (*countptr + add < *countptr) {
+ errno = ENOMEM;
+ return -1;
+ }
+ res = virReallocN(ptrptr, size, *countptr + add);
+ if (res == 0) {
+ memset(*(char **)ptrptr + (size * *countptr), 0, size * add);
+ *countptr += add;
+ }
+ return res;
+}
+
+/**
+ * virShrinkN:
+ * @ptrptr: pointer to pointer for address of allocated memory
+ * @size: number of bytes per element
+ * @countptr: pointer to number of elements in array
+ * @remove: number of elements to remove
+ *
+ * Resize the block of memory in 'ptrptr' to be an array of
+ * '*countptr' - 'remove' elements, each 'size' bytes in length.
+ * Update 'ptrptr' and 'countptr' with the details of the newly
+ * allocated memory. If 'remove' is larger than 'countptr', free
+ * the entire array.
+ */
+void virShrinkN(void *ptrptr, size_t size, size_t *countptr, size_t remove)
+{
+ if (remove < *countptr)
+ ignore_value(virReallocN(ptrptr, size, *countptr -= remove));
+ else {
+ virFree(ptrptr);
+ *countptr = 0;
+ }
+}
+
+
+/**
* Vir_Alloc_Var:
* @ptrptr: pointer to hold address of allocated memory
* @struct_size: size of initial struct
diff --git a/src/util/memory.h b/src/util/memory.h
index 60e2be6..98ac2b3 100644
--- a/src/util/memory.h
+++ b/src/util/memory.h
@@ -46,14 +46,21 @@
/* Don't call these directly - use the macros below */
-int virAlloc(void *ptrptr, size_t size) ATTRIBUTE_RETURN_CHECK;
-int virAllocN(void *ptrptr, size_t size, size_t count) ATTRIBUTE_RETURN_CHECK;
-int virReallocN(void *ptrptr, size_t size, size_t count) ATTRIBUTE_RETURN_CHECK;
+int virAlloc(void *ptrptr, size_t size) ATTRIBUTE_RETURN_CHECK
+ ATTRIBUTE_NONNULL(1);
+int virAllocN(void *ptrptr, size_t size, size_t count) ATTRIBUTE_RETURN_CHECK
+ ATTRIBUTE_NONNULL(1);
+int virReallocN(void *ptrptr, size_t size, size_t count) ATTRIBUTE_RETURN_CHECK
+ ATTRIBUTE_NONNULL(1);
+int virExpandN(void *ptrptr, size_t size, size_t *count, size_t add)
+ ATTRIBUTE_RETURN_CHECK ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(3);
+void virShrinkN(void *ptrptr, size_t size, size_t *count, size_t remove)
+ ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(3);
int virAllocVar(void *ptrptr,
size_t struct_size,
size_t element_size,
- size_t count) ATTRIBUTE_RETURN_CHECK;
-void virFree(void *ptrptr);
+ size_t count) ATTRIBUTE_RETURN_CHECK ATTRIBUTE_NONNULL(1);
+void virFree(void *ptrptr) ATTRIBUTE_NONNULL(1);
/**
* VIR_ALLOC:
@@ -87,12 +94,44 @@ void virFree(void *ptrptr);
*
* Re-allocate an array of 'count' elements, each sizeof(*ptr)
* bytes long and store the address of allocated memory in
- * 'ptr'. Fill the newly allocated memory with zeros
+ * 'ptr'. If 'ptr' grew, the added memory is uninitialized.
*
* Returns -1 on failure, 0 on success
*/
# define VIR_REALLOC_N(ptr, count) virReallocN(&(ptr), sizeof(*(ptr)), (count))
+/**
+ * VIR_EXPAND_N:
+ * @ptr: pointer to hold address of allocated memory
+ * @count: variable tracking number of elements currently allocated
+ * @add: number of elements to add
+ *
+ * Re-allocate an array of 'count' elements, each sizeof(*ptr)
+ * bytes long, to be 'count' + 'add' elements long, then store the
+ * address of allocated memory in 'ptr' and the new size in 'count'.
+ * The new elements are filled with zero.
+ *
+ * Returns -1 on failure, 0 on success
+ */
+# define VIR_EXPAND_N(ptr, count, add) \
+ virExpandN(&(ptr), sizeof(*(ptr)), &(count), add)
+
+/**
+ * VIR_SHRINK_N:
+ * @ptr: pointer to hold address of allocated memory
+ * @count: variable tracking number of elements currently allocated
+ * @remove: number of elements to remove
+ *
+ * Re-allocate an array of 'count' elements, each sizeof(*ptr)
+ * bytes long, to be 'count' - 'remove' elements long, then store the
+ * address of allocated memory in 'ptr' and the new size in 'count'.
+ * If 'count' <= 'remove', the entire array is freed.
+ *
+ * No return value.
+ */
+# define VIR_SHRINK_N(ptr, count, remove) \
+ virShrinkN(&(ptr), sizeof(*(ptr)), &(count), remove)
+
/*
* VIR_ALLOC_VAR_OVERSIZED:
* @M: size of base structure
--
1.7.2.1
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