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Date: Mon, 28 Aug 2006 16:29:51 -0400 (EDT) From: Alan Stern <stern@...land.harvard.edu> To: Andrew Morton <akpm@...l.org>, Ingo Molnar <mingo@...hat.com> cc: Kernel development list <linux-kernel@...r.kernel.org> Subject: [PATCH 3/3] 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@...land.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 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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