block/backup: support bitmap sync modes for non-bitmap backups

[qemu.git] / HACKING

diff --git a/HACKING b/HACKING
index 058aa8fd491243cc1838f0d2ab759afc4b0453d1..0fc3e0fc04fe6ad00ceb954c25319aa522d5af64 100644 (file)
--- a/HACKING
+++ b/HACKING
@@ -1,10 +1,28 @@
 1. Preprocessor
 
+1.1. Variadic macros
+
 For variadic macros, stick with this C99-like syntax:
 
 #define DPRINTF(fmt, ...)                                       \
     do { printf("IRQ: " fmt, ## __VA_ARGS__); } while (0)
 
+1.2. Include directives
+
+Order include directives as follows:
+
+#include "qemu/osdep.h"  /* Always first... */
+#include <...>           /* then system headers... */
+#include "..."           /* and finally QEMU headers. */
+
+The "qemu/osdep.h" header contains preprocessor macros that affect the behavior
+of core system headers like <stdint.h>.  It must be the first include so that
+core system headers included by external libraries get the preprocessor macros
+that QEMU depends on.
+
+Do not include "qemu/osdep.h" from header files since the .c file will have
+already included it.
+
 2. C types
 
 It should be common sense to use the right type, but we have collected
@@ -100,6 +118,15 @@ Please note that g_malloc will exit on allocation failure, so there
 is no need to test for failure (as you would have to with malloc).
 Calling g_malloc with a zero size is valid and will return NULL.
 
+Prefer g_new(T, n) instead of g_malloc(sizeof(T) * n) for the following
+reasons:
+
+  a. It catches multiplication overflowing size_t;
+  b. It returns T * instead of void *, letting compiler catch more type
+     errors.
+
+Declarations like T *v = g_malloc(sizeof(*v)) are acceptable, though.
+
 Memory allocated by qemu_memalign or qemu_blockalign must be freed with
 qemu_vfree, since breaking this will cause problems on Win32.
 
@@ -158,6 +185,10 @@ painful. These are:
  * you may assume that right shift of a signed integer duplicates
    the sign bit (ie it is an arithmetic shift, not a logical shift)
 
+In addition, QEMU assumes that the compiler does not use the latitude
+given in C99 and C11 to treat aspects of signed '<<' as undefined, as
+documented in the GNU Compiler Collection manual starting at version 4.0.
+
 7. Error handling and reporting
 
 7.1 Reporting errors to the human user