Re: Fix nptl/tst-cancel7 for non-bash shells

["Carlos O'Donell" <carlos at systemhalted dot org>]

On Mon, Oct 29, 2012 at 12:02 PM, Rich Felker <dalias@aerifal.cx> wrote:
> On Mon, Oct 29, 2012 at 09:37:34AM -0400, Carlos O'Donell wrote:
>> On Sun, Oct 28, 2012 at 9:15 PM, Rich Felker <dalias@aerifal.cx> wrote:
>> > This issue caused me to take a look at the implementation of system's
>> > handling of cancellation, which turns out to have a serious bug:
>> >
>> > http://sourceware.org/bugzilla/show_bug.cgi?id=14782
>> >
>> > It should be easy to fix; the fix is a purely-red patch (all -'s).
>>
>> While your analysis looks correct the more interesting question to me
>> is "Why was this added in the first place?" Can you dig a bit more and
>> see if we can determine the reason for the deviation from the standard?
>> Clearly we went to a lot of work to implement the current behaviour and
>> I'd like to know why.
>
> Where would you suggest I start? "system" is not the easiest function
> to search the bug tracker for, but I just did and the only resolved
> bugs I found related to system were invalid (requests for it to close
> the parent's file descriptors or catch the SIGCHLD). As such, I don't
> think this code was written to fix any bug.

I recommend:

(1) Use gitweb to browse the history of the changes in the files
    and lines of code that implement the change. Alternatively use
    `git blame`, `git log` and `git diff ...`.

(2) Try to track the changes down to a commit.

(3) With commit in hand cross-reference the mailing list i.e. libc-hacker
    and libc-alpha, and find the post related to the commit.
    The related post usually has an explanation about why the author
    made the change.

You might get to (3) and find no such reference in which case we did
our due-diligence and we're done.

Cheers,
Carlos.