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Re: [PATCH] iotests: Quote $cmd in _send_qemu_cmd


From: Max Reitz
Subject: Re: [PATCH] iotests: Quote $cmd in _send_qemu_cmd
Date: Tue, 15 Dec 2020 13:14:36 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0

On 15.12.20 12:43, Kevin Wolf wrote:
Am 14.12.2020 um 18:58 hat Max Reitz geschrieben:
With bash 5.1, the output of the following script (which creates an
array with a single element, then takes a single-element slice from that
array, and echos the result) changes:

   a=("double  space")
   a=${a[@]:0:1}
   echo "$a"

from "double space" to "double  space", i.e. all white space is
preserved as-is.  This is probably what we actually want here (judging
from the "...to accommodate pathnames with spaces" comment), but before
5.1, we have to quote the ${} slice to get the same behavior.

In any case, without quoting, the reference output of many iotests is
different between bash 5.1 and pre-5.1, which is not very good.  We
should fix it by quoting here, and then adjusting all the reference
output of all iotests using _send_qemu_cmd accordingly.  (The only
ones we do not need to change are those that do not have multiple
consecutive whitespaces in their _send_qemu_cmd parameters.)

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
Alternatively, we could explicitly collapse all whitespace sequences
into single spaces, but I believe that would defeat the purpose of
"accomodat[ing] pathnames with spaces".

I agree that quoting is the better alternative.

The whole thing shouldn't be needed if callers propertly quote
filenames. If I understand correctly, these lines just try to merge
back filenames that have been split into multiple words because the
caller wasn't careful. But we can't reliably do that because we don't
know which and how much whitespace was removed.

No, without quoting here, the slice operation will actually collapse spaces inside of array elements, as shown in the commit message (a=("x y") creates an array with a single element that just has two spaces in it). If the caller didn’t quote, then quoting in _send_qemu_cmd wouldn’t help either, because the whitespace would no longer be present in $@.

Most callers of _send_qemu_cmd actually do something like this:

_send_qemu_cmd \
    $QEMU_HANDLE \
    "{ 'execute': 'something',
       'arguments': ... }" \
    'return'

So they do quote all of their arguments, and actually only pass three (or four, with success_or_failure=y), so basically the slicing is generally unnecessary and we’d just need cmd=$1 (not $2, because _send_qemu_cmd likes to invoke “shift”).

In fact, if you do that on top of this patch (cmd=$1 instead of the fancy slice), you’ll see that the only test that then doesn’t pass is 102. I think that’s because it has this one _send_qemu_cmd invocation that forgot to pass $QEMU_HANDLE...?

So, alternatively to quoting the slice, we could also just set cmd=$1 and fix 102.

I used this script to verify that the git-diff only changes whitespace
(except for the hunk in common.qemu):

   https://gist.github.com/XanClic/41cfcc2ac4619421883e8a97790f5c9e

'git diff --word-diff' is good enough for me.

Learn a new thing every day.

This seems to be based on your branch (312.out doesn't exist yet for
me), so instead of merging, you can just have my:

Reviewed-by: Kevin Wolf <kwolf@redhat.com>

In any case (because perhaps we just want cmd=$1, I don’t know), thanks. :)

Max




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