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Re: [Qemu-devel] [PATCH] qemu-io: Reinitialize optind correctly before p
Re: [Qemu-devel] [PATCH] qemu-io: Reinitialize optind correctly before parsing inner command.
Wed, 2 Jan 2019 17:21:08 -0600
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On 12/30/18 12:09 PM, Richard W.M. Jones wrote:
> On FreeBSD 11.2:
> $ ./qemu-io -f raw -c "aio_write 0 512" "nbd:localhost:10809"
> Parsing error: non-numeric argument, or extraneous/unrecognized suffix --
> After main option parsing, we reinitialize optind so we can parse each
> command. The error happens when parsing the aio_write command. After
> the aio_write getopt loop, optind == 0 and argv[optind] points to the
> command name ("aio_write" in this case). The code fails because it
> tries to parse argv[optind] (which it thinks is the first argument) as
> an integer.
> In fact optind _starts_ the loop as 0, because we set it to 0.
> 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.
> (From the rest of the man page it is clear that optind must be
> reinitialized to 1).
> Unfortunately this conflicts with the glibc man page which says:
> A program that scans multiple argument vectors, or rescans the same
> vector more than once, and wants to make use of GNU extensions such as
> '+' and '-' at the start of optstring, or changes the value of
> POSIXLY_CORRECT between scans, must reinitialize getopt() by resetting
> optind to 0, rather than the traditional value of 1. (Resetting to 0
> forces the invocation of an internal initialization routine that
> rechecks POSIXLY_CORRECT and checks for GNU extensions in optstring.)
The glibc manual implies that setting optind = 1 is a weak reset
(sufficient if you are NOT using either leading '+' or '-', and if you
do NOT expect POSIXLY_CORRECT to have changed value since the last
time), and that optind = 0 is a hard reset needed only when the weak
reset is insufficient.
> Reinitialize optind to either 0 or 1 depending on whether we're using
> glibc or not.
> I didn't set optreset - it's not present in glibc and it doesn't seem
> to make any difference on FreeBSD.
BSD has optreset as its way of forcing hard reset (instead of optind=0),
but both platforms allow optind=1 for soft reset.
> Signed-off-by: Richard W.M. Jones <address@hidden>
> qemu-io-cmds.c | 4 ++++
> 1 file changed, 4 insertions(+)
Given that none of our uses of getopt() in qemu-io-cmds.c rely on
leading '+' or '-', and that we don't call setenv() to change
POSIXLY_CORRECT on the fly, I think the simpler patch is to just blindly
set optind = 1 when we want a soft reset, as a hard reset is overkill
for our needs.
> diff --git a/qemu-io-cmds.c b/qemu-io-cmds.c
> index 2c39124036..ca4e258579 100644
> --- a/qemu-io-cmds.c
> +++ b/qemu-io-cmds.c
> @@ -114,7 +114,11 @@ static int command(BlockBackend *blk, const cmdinfo_t
> *ct, int argc,
> +#ifdef __GNU_LIBRARY__
> optind = 0;
> + optind = 1;
and thus we don't need the #ifdef __GNU_LIBRARY__ code, nor the syntax
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org
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