Re: [Xen-devel] [PATCH v2 3/5] libxl: xsrestrict QEMU

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Stefano Stabellini writes ("[PATCH v2 3/5] libxl: xsrestrict QEMU"):
> Check whether QEMU supports the xsrestrict option, by parsing its --help
> output. Store the result on xenstore for future reference on a per QEMU
> binary basis, so that device_model_override still works fine with it.
...
> +    pid = fork();
> +    if (pid < 0)
> +        return ERROR_FAIL;

Sadly, direct use of fork is forbidden.  See the doc comment for
libxl__ev_child_fork.

I hereby volunteer to fix this.  But we should probably wait for this
series to settle down a bit first, as what you have done is suitable
for testing with xl, at least.

For now, please add a note to the commit message subject ("WIP" or
"RFC" or something).


And, I spotted this:

> +    /* father parses the output */

Normally we use "parent" rather than imputing gender to processes...


> +    s = libxl__strdup(gc, dm);
> +    libxl__replace_chr(gc, s, '/', '_');
> +    s = libxl__sprintf(gc, "libxl/%s/%s", s, opt);
> +    buf = libxl__xs_read(gc, XBT_NULL, s);
> +    if (buf != NULL)
> +        return !strcmp(buf, "1");

This cacheing mechanism is pretty nasty.  Wouldn't it be better to
save the qemu help output in a disk file, or something ?


Ian.

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