[Qemu-devel] [PATCH 2/5] CODING_STYLE: add C type rules

[Blue Swirl]

Add C type rules from libvirt HACKING. Also include
a description of special QEMU scalar types.

Signed-off-by: Blue Swirl <address@hidden>
---
 CODING_STYLE |   56 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 56 insertions(+), 0 deletions(-)

diff --git a/CODING_STYLE b/CODING_STYLE
index c4c09ab..3f10d72 100644
--- a/CODING_STYLE
+++ b/CODING_STYLE
@@ -92,3 +92,59 @@ indentation to track nesting:
 #if defined(HAVE_POSIX_FALLOCATE) && !defined(HAVE_FALLOCATE)
 # define fallocate(a,ignored,b,c) posix_fallocate(a,b,c)
 #endif
+
+6. C types
+
+Use the right type.
+
+6.1. Scalars
+
+If you're using "int" or "long", odds are good that there's a better type.
+If a variable is counting something, be sure to declare it with an
+unsigned type.
+If it's memory-size-related, use size_t (use ssize_t only if required).
+If it's file-size related, use uintmax_t, or maybe off_t.
+If it's file-offset related (i.e., signed), use off_t.
+If it's just counting small numbers use "unsigned int";
+(on all but oddball embedded systems, you can assume that that
+type is at least four bytes wide).
+
+In the event that you require a specific width, use a standard type like
+int32_t, uint32_t, uint64_t, etc.  The specific types are mandatory for
+vmstate.
+
+Don't use Linux kernel internal types like u32, __u32 or __le32.
+
+Use target_phys_addr_t for hardware physical addresses except pcibus_t
+for PCI addresses.  Use target_ulong (or abi_ulong) for CPU
+virtual addresses, however devices should not need to use target_ulong.
+
+While using "bool" is good for readability, it comes with minor caveats:
+ - Don't use "bool" in places where the type size must be constant across
+   all systems, like public interfaces and on-the-wire protocols.
+ - Don't compare a bool variable against the literal, "true",
+   since a value with a logical non-false value need not be "1".
+   I.e., don't write "if (seen == true) ...".  Rather, write "if (seen)...".
+
+Of course, take all of the above with a grain of salt.  If you're about
+to use some system interface that requires a type like size_t, pid_t or
+off_t, use matching types for any corresponding variables.
+
+Also, if you try to use e.g., "unsigned int" as a type, and that
+conflicts with the signedness of a related variable, sometimes
+it's best just to use the *wrong* type, if "pulling the thread"
+and fixing all related variables would be too invasive.
+
+Finally, while using descriptive types is important, be careful not to
+go overboard.  If whatever you're doing causes warnings, or requires
+casts, then reconsider or ask for help.
+
+6.2. Pointers
+
+Ensure that all of your pointers are "const-correct".
+Unless a pointer is used to modify the pointed-to storage,
+give it the "const" attribute.  That way, the reader knows
+up-front that this is a read-only pointer.  Perhaps more
+importantly, if we're diligent about this, when you see a non-const
+pointer, you're guaranteed that it is used to modify the storage
+it points to, or it is aliased to another pointer that is.
-- 
1.6.2.4