Date: Fri, 16 Dec 2016 13:15:01 -0500 From: Rich Felker <dalias@...c.org> To: musl@...ts.openwall.com Subject: getsubopt behavior POSIX leaves a lot about getsubopt under-specified: http://pubs.opengroup.org/onlinepubs/9699919799/functions/getsubopt.html It's not clear what happens to any of the pointed-to objects in the case where no keys match, but it seems generally agreed upon that *optionp advances to the next option (or end of string) and that the separator ',' if any is nulled out. What's explicitly not specified is what happens to *valuep when getsubopt returns -1 (no key match): "APPLICATION USAGE The value of *valuep when getsubopt() returns -1 is unspecified. Historical implementations provide various incompatible extensions to allow an application to access the suboption text that was not found in the keylistp array." Glibc updates *valuep to point to the original value of *optionp (the whole "unrecognized_key=value" component, with any final ',' nulled out). This is rather useless, since the caller can just save the old value of *optionp and use it when getsubopt returns -1, but I found some code in v4l2-ctl that depends on it: https://git.linuxtv.org/v4l-utils.git/tree/utils/v4l2-ctl/v4l2-ctl-common.cpp?id=fd7e1db71eabbb81ff20a2ab97948612ef061edf#n693 On the other hand, FreeBSD nulls the pointer at *valuep, any final ',', AND any '=' character in the unrecognized subopt string, so that the "unrecognized_key=value" component is not even easily recoverable: https://github.com/freebsd/freebsd/blob/22c7ee83f61dc73c60942c528108e8b6220ed350/lib/libc/stdlib/getsubopt.c Reportedly Solaris and other sysv-type implementations match the glibc behavior. musl currently nulls the pointer at *valuep but doesn't clobber the '='. Being that POSIX allows any of them (by leaving it unspecified) and that the BSD behavior is actively destructive and undesirable (and perhaps not even conforming in that it clobbers data it doesn't seem to be specified to clobber), my leaning is to adopt the glibc/sysv behavior. Note that the Linux man page documents the glibc behavior without documenting as an extensions: "Otherwise, -1 is returned and *valuep is the entire name[=value] string." Source: http://man7.org/linux/man-pages/man3/getsubopt.3.html Thoughts? Rich
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