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authorAlan Stern <stern@rowland.harvard.edu>2006-09-29 02:01:21 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2006-09-29 09:18:22 -0700
commitc16a02d6f5fcfe05dc6fd40aa80a8e1d055300db (patch)
tree9335cbe024a12723395a92f5aeca7111700a0766 /Documentation/CodingStyle
parentfdf8cb0909b531f9ae8f9b9d7e4eb35ba3505f07 (diff)
downloadlinux-c16a02d6f5fcfe05dc6fd40aa80a8e1d055300db.tar.gz
[PATCH] Add section on function return values to CodingStyle
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> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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@@ -532,6 +532,40 @@ appears outweighs the potential value of the hint that tells gcc to do
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