Re: [PATCH v5 14/50] mutli-process: build remote command line args

[Elena Ufimtseva]

On Wed, Mar 04, 2020 at 11:00:32AM +0000, Daniel P. Berrangé wrote:
> On Mon, Mar 02, 2020 at 02:39:37PM -0800, Elena Ufimtseva wrote:
> > On Mon, Mar 02, 2020 at 05:47:45PM +0000, Daniel P. Berrangé wrote:
> > > On Mon, Mar 02, 2020 at 06:36:13PM +0100, Philippe Mathieu-Daudé wrote:
> > > > typo "multi" in patch subject.
> > > >
> > Thank Philippe, will fix.
> >  
> > > > On 2/24/20 9:55 PM, Jagannathan Raman wrote:
> > > > > From: Elena Ufimtseva <address@hidden>
> > > > > 
> > > > > Signed-off-by: Elena Ufimtseva <address@hidden>
> > > > > Signed-off-by: Jagannathan Raman <address@hidden>
> > > > > Signed-off-by: John G Johnson <address@hidden>
> > > > > ---
> > > > >   v4 -> v5:
> > > > >    - Added "exec" suboption to get the executable's name
> > > > >    - Addressed feedback about variable names
> > > > >    - Removed redundant check for spawning a process
> > > > > 
> > > > >   hw/proxy/qemu-proxy.c         | 68 
> > > > > +++++++++++++++++++++++++++++++++----------
> > > > >   include/hw/proxy/qemu-proxy.h |  2 +-
> > > > >   2 files changed, 54 insertions(+), 16 deletions(-)
> > > > > 
> > > > > diff --git a/hw/proxy/qemu-proxy.c b/hw/proxy/qemu-proxy.c
> > > > > index 828bbd7..d792e86 100644
> > > > > --- a/hw/proxy/qemu-proxy.c
> > > > > +++ b/hw/proxy/qemu-proxy.c
> > > > > @@ -19,19 +19,50 @@
> > > > >   static void pci_proxy_dev_realize(PCIDevice *dev, Error **errp);
> > > > > +static int add_argv(char *opts_str, char **argv, int argc)
> > > > > +{
> > > > > +    int max_args = 64;
> > > > > +
> > > > > +    if (argc < max_args - 1) {
> > > > > +        argv[argc++] = opts_str;
> > > > > +        argv[argc] = 0;
> > > > > +    } else {
> > > > > +        return 0;
> > > > > +    }
> > > > > +
> > > > > +    return argc;
> > > > > +}
> > > > > +
> > > > > +static int make_argv(char *opts_str, char **argv, int argc)
> > > > > +{
> > > > > +    int max_args = 64;
> > > > > +
> > > > > +    char *p2 = strtok(opts_str, " ");
> > > > > +    while (p2 && argc < max_args - 1) {
> > > > > +        argv[argc++] = p2;
> > > > > +        p2 = strtok(0, " ");
> > > > > +    }
> > > > > +    argv[argc] = 0;
> > > > 
> > > > Is there a GLib function to do that?
> > >
> > 
> > Hi Daniel
> > 
> > > g_shell_parse_argv() perhaps
> > >
> > 
> > Thanks for the suggestion.
> > 
> > >   
> > > https://developer.gnome.org/glib/stable/glib-Shell-related-Utilities.html
> > > 
> > > 
> > > Though my preference would be to avoid the need to do this at all, by
> > > not accepting a raw shell command line string in the first place.
> > >
> > Can you please clarify? Did you mean that it would be better if Qemu somehow
> > verifies the options and then passes it to a remote process via a message?
> 
> I've not been able to trace the code paths back all the way, so I can't
> point to where I think needs fixing. I assuming that something, somewhere
> in this patch series should starts out with a binary name and a list of argv
> as an array of char *. ie a "char **argv".  At some point this array gets
> mashed together into a single 'char *' string where all the argv are separated
> by a space. This patch now tries to parse this and turn it back into a
> "char **argv" array.
> 
> So my key point is that we should try hard to avoid this intermediate
> shell command line string stage entirely. Always keep the argv in an array
> form, and never mash them together such that they then need parsing again.
>
Hi Daniel

Thank you for explanation.
At this point there is no intermediate stage as we grab the arguments
as a raw string from the command line option -remote:

-remote rid=8,exec=qemu-scsi-dev,command="-drive 
id=drive_image2,,file=/root/remote-process-disk.img"

So the command="" string is being later parsed into the array and remote process
gets spawned with the "char **argv".

Stefan expressed his concern that its not convenient to use due to
the double escaping commas, spaces, quotes and we do agree with that.
We were seeking an advice on what is the better approach.

Few things we discussed internally is to have the remote drive
command line options passed over by messages or using QMP.

Thank you!
Elena


> I understand this is probably more complex, because we're having to pass
> this across processes, via QemuOpts IIUC, but I still believe it is important
> to have this data kept in array format if at all practical.
> 
> Regards,
> Daniel
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