From: Alan Stern Date: Fri, 29 Sep 2006 09:01:21 +0000 (-0700) Subject: [PATCH] Add section on function return values to CodingStyle X-Git-Tag: v2.6.19-rc1~687 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c16a02d6f5fcfe05dc6fd40aa80a8e1d055300db;p=linux-2.6 [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 Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/Documentation/CodingStyle b/Documentation/CodingStyle index 6d2412ec91..29c18966b0 100644 --- a/Documentation/CodingStyle +++ b/Documentation/CodingStyle @@ -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