[PATCH 3/3] Add section on function return values to CodingStyle

[PATCH 3/3] Add section on function return values to CodingStyle

[Alan Stern]

This patch (as776) adds a new chapter to Documentation/CodingStyle,
explaining the circumstances under which a function should return
0 for failure and non-zero for success as opposed to a negative
error code for failure and 0 for success.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>

Index: mm/Documentation/CodingStyle
===================================================================
--- mm.orig/Documentation/CodingStyle
+++ mm/Documentation/CodingStyle
@@ -532,6 +532,40 @@ appears outweighs the potential value of
 something it would have done anyway.
 
 
+		Chapter 16: Function return values and names
+
+Functions can return values of many different kinds, and one of the
+most common is a value indicating whether the function succeeded or
+failed.  Such a value can be represented as an error-code integer
+(-Exxx = failure, 0 = success) or a "succeeded" boolean (0 = failure,
+non-zero = success).
+
+Mixing up these two sorts of representations is a fertile source of
+difficult-to-find bugs.  If the C language included a strong distinction
+between integers and booleans then the compiler would find these mistakes
+for us... but it doesn't.  To help prevent such bugs, always follow this
+convention:
+
+	If the name of a function is an action or an imperative command,
+	the function should return an error-code integer.  If the name
+	is a predicate, the function should return a "succeeded" boolean.
+
+For example, "add work" is a command, and the add_work() function returns 0
+for success or -EBUSY for failure.  In the same way, "PCI device present" is
+a predicate, and the pci_dev_present() function returns 1 if it succeeds in
+finding a matching device or 0 if it doesn't.
+
+All EXPORTed functions must respect this convention, and so should all
+public functions.  Private (static) functions need not, but it is
+recommended that they do.
+
+Functions whose return value is the actual result of a computation, rather
+than an indication of whether the computation succeeded, are not subject to
+this rule.  Generally they indicate failure by returning some out-of-range
+result.  Typical examples would be functions that return pointers; they use
+NULL or the ERR_PTR mechanism to report failure.
+
+
 
 		Appendix I: References