On 1/7/19 11:17 AM, Max Reitz wrote: > On 03.01.19 10:47, Richard W.M. Jones wrote: >> On FreeBSD 11.2: >> >> $ nbdkit memory size=1M --run './qemu-io -f raw -c "aio_write 0 512" $nbd' >> Parsing error: non-numeric argument, or extraneous/unrecognized suffix -- >> aio_write >> >> After main option parsing, we reinitialize optind so we can parse each >> command. However reinitializing optind to 0 does not work on FreeBSD. >> What happens when you do this is optind remains 0 after the option >> parsing loop, and the result is we try to parse argv[optind] == >> argv[0] == "aio_write" as if it was the first parameter. >> >> The FreeBSD manual page says: >> >> In order to use getopt() to evaluate multiple sets of arguments, or to >> evaluate a single set of arguments multiple times, the variable optreset >> must be set to 1 before the second and each additional set of calls to >> getopt(), and the variable optind must be reinitialized. > > [...] > >> Note I didn't set optreset. It's not present in glibc and the "hard >> reset" is not necessary in this context. > > But it sure sounds like FreeBSD requires you to set it, doesn't it?
The reason BSD and glibc have a hard reset path is because of hidden state - both BSD and glibc track state that remembers if the options began with '+' or '-' (both of those are extensions beyond POSIX), and whether POSIXLY_CORRECT was set. Beyond that hidden state is a corner case of one more piece of state that you can trigger using only POSIX: if the user passes './prog -ab' while you had code: swich (getopt(argc, argv, "ab")) { case 'a': optind = 1; ... then things fall apart for both BSD and glibc, because getopt() has to track invisible state in order to remember that the next call will process the -b portion of the merged short-option in argv[optind==1] rather than repeating the -a half and before moving on to optind==2. But this latter corner case can only happen when getopt() did not return -1. At the end of the day, both GNU optind=0 and BSD optreset=1 are sufficient to force a hard reset of all hidden state. But if you don't use POSIX extensions, and always run getopt() until a -1 return, then setting optind=1 is a portable soft reset, regardless of how the hidden state is implemented, and regardless of how (or even if) libc offers a hard reset, even though POSIX itself is currently lacking that mention. (I should probably file a POSIX defect to get that wording listed in POSIX) -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org
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