Re: [Qemu-devel] [PATCH 04/27] vl: convert -m to qemu_opts_parse()

[Igor Mammedov <imammedo@redhat.com>]

On Thu, 21 Nov 2013 11:12:43 +0100
Markus Armbruster <armbru@redhat.com> wrote:

> Igor Mammedov <imammedo@redhat.com> writes:
> 
> > Along with conversion extend -m option to support following parameters:
> 
> Please split this into two patches: first conversion to QemuOpts, then
> extension.
> 
> >   "mem" - startup memory amount
> >   "slots" - total number of hotplug memory slots
> >   "maxmem" - maximum possible memory
> >
> > "slots" and "maxmem" should go in pair and "maxmem" should be greater
> > than "mem" for memory hotplug to be usable.
> >
> > v2:
> >   make sure maxmem is not less than ram size
> >
> > Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> > ---
> >  qemu-options.hx |    9 +++++-
> >  vl.c            |   73 ++++++++++++++++++++++++++++++++++++++++++++++---------
> >  2 files changed, 68 insertions(+), 14 deletions(-)
> >
> > diff --git a/qemu-options.hx b/qemu-options.hx
> > index 8b94264..fe4559b 100644
> > --- a/qemu-options.hx
> > +++ b/qemu-options.hx
> > @@ -210,8 +210,13 @@ use is discouraged as it may be removed from future versions.
> >  ETEXI
> >  
> >  DEF("m", HAS_ARG, QEMU_OPTION_m,
> > -    "-m megs         set virtual RAM size to megs MB [default="
> > -    stringify(DEFAULT_RAM_SIZE) "]\n", QEMU_ARCH_ALL)
> > +    "-m [mem=]megs[,slots=n,maxmem=size]\n"
> > +    "                set virtual RAM size to megs MB [default="
> > +    stringify(DEFAULT_RAM_SIZE) "]\n"
> > +    "                mem=start-up memory amount\n"
> > +    "                slots=maximum number of hotplug slots\n"
> > +    "                maxmem=maximum total amount of memory\n",
> > +    QEMU_ARCH_ALL)
> 
> Help text is confusing, because it discusses megs twice.  Fits right in,
> as output of -help is generally confusing (to put it politely).
> 
> What about something like this:
> 
> -m [mem=]megs[,slots=n,maxmem=size]
>                 configure guest RAM
>                 mem: initial amount of guest memory (default: XXX)
>                 slots: number of hotplug slots (default: none)
>                 maxmem: maximum amount of guest memory (default: mem)
Sure, I'll fix it.

> >  STEXI
> >  @item -m @var{megs}
> >  @findex -m
> > diff --git a/vl.c b/vl.c
> > index f28674f..5974f0f 100644
> > --- a/vl.c
> > +++ b/vl.c
> > @@ -529,6 +529,28 @@ static QemuOptsList qemu_msg_opts = {
> >      },
> >  };
> >  
> > +static QemuOptsList qemu_mem_opts = {
> > +    .name = "memory-opts",
> > +    .implied_opt_name = "mem",
> > +    .head = QTAILQ_HEAD_INITIALIZER(qemu_mem_opts.head),
> > +    .merge_lists = true,
> 
> Yes, because multiple -m need to accumulate.
> 
> > +    .desc = {
> > +        {
> > +            .name = "mem",
> > +            .type = QEMU_OPT_SIZE,
> > +        },
> > +        {
> > +            .name = "slots",
> > +            .type = QEMU_OPT_NUMBER,
> > +        },
> > +        {
> > +            .name = "maxmem",
> > +            .type = QEMU_OPT_SIZE,
> > +        },
> > +        { /* end of list */ }
> > +    },
> > +};
> > +
> >  /**
> >   * Get machine options
> >   *
> > @@ -2816,6 +2838,14 @@ static int object_create(QemuOpts *opts, void *opaque)
> >      return 0;
> >  }
> >  
> > +static void qemu_init_default_mem_opts(uint64_t size)
> > +{
> > +    QemuOpts *opts = qemu_opts_create_nofail(&qemu_mem_opts);
> > +    qemu_opt_set_number(opts, "mem", size);
> > +    qemu_opt_set_number(opts, "maxmem", size);
> > +    qemu_opt_set_number(opts, "slots", 0);
> > +}
> > +
> 
> We usually don't put defaults in QemuOpts.  Instead, the code querying
> QemuOpts detects and handles absence of the parameter.  Can be as simple
> as qemu_opt_get_size(opts, "mem", DEFAULT_RAM_SIZE * 1024 * 1024).
It allows to make number of uses a bit simpler:

for example v6:
    QemuOpts *opts = qemu_opts_find(qemu_find_opts("memory-opts"), NULL);
    if (!opts) { /* no -m x,... was passed to cmd line so no mem hotplug */
        return;
    }
    mem_st->dev_count = qemu_opt_get_number(opts, "slots", 0);

becomes"
    QemuOpts *opts = qemu_opts_find(qemu_find_opts("memory-opts"), NULL);
    state->dev_count = qemu_opt_get_number(opts, "slots", 0);
    
and eliminates need to pepper code with DEFAULT_RAM_SIZE * 1024 * 1024 or
like constants wherever qemu_opt_get_..() is called, that was main reason
to set defaults. i.e. set defaults only once instead of spreading them in
every place qemu_opt_get_..() is called.

> 
> See also below.
> 
> >  int main(int argc, char **argv, char **envp)
> >  {
> >      int i;
> > @@ -2887,6 +2917,7 @@ int main(int argc, char **argv, char **envp)
> >      qemu_add_opts(&qemu_tpmdev_opts);
> >      qemu_add_opts(&qemu_realtime_opts);
> >      qemu_add_opts(&qemu_msg_opts);
> > +    qemu_add_opts(&qemu_mem_opts);
> >  
> >      runstate_init();
> >  
> > @@ -2901,7 +2932,8 @@ int main(int argc, char **argv, char **envp)
> >      module_call_init(MODULE_INIT_MACHINE);
> >      machine = find_default_machine();
> >      cpu_model = NULL;
> > -    ram_size = 0;
> > +    ram_size = DEFAULT_RAM_SIZE * 1024 * 1024;
> > +    qemu_init_default_mem_opts(ram_size);
> >      snapshot = 0;
> >      cyls = heads = secs = 0;
> >      translation = BIOS_ATA_TRANSLATION_AUTO;
> > @@ -3178,21 +3210,43 @@ int main(int argc, char **argv, char **envp)
> >                  exit(0);
> >                  break;
> >              case QEMU_OPTION_m: {
> > -                int64_t value;
> >                  uint64_t sz;
> > -                char *end;
> > +                const char *end;
> > +                char *s;
> >  
> > -                value = strtosz(optarg, &end);
> > -                if (value < 0 || *end) {
> > -                    fprintf(stderr, "qemu: invalid ram size: %s\n", optarg);
> > +                opts = qemu_opts_parse(qemu_find_opts("memory-opts"),
> > +                                       optarg, 1);
> > +                if (!opts) {
> >                      exit(1);
> >                  }
> > -                sz = QEMU_ALIGN_UP((uint64_t)value, 8192);
> > +
> > +                /* fixup legacy sugffix-less format */
> 
> /* fix up legacy suffix-less format */
> 
> The problem here is that OPT_SIZE treats values without a size suffix as
> bytes, but we need to default to MiB for backward compatibility.
> 
> > +                end = qemu_opt_get(opts, "mem");
> > +                if (g_ascii_isdigit(end[strlen(end) - 1])) {
> > +                    s = g_strconcat(end, "M", NULL);
> > +                    qemu_opt_set(opts, "mem", s);
> > +                    g_free(s);
> > +                }
> 
> Ugly.
> 
> Why is the variable called 'end'?
would be 'suffix' better?

> 
> qemu_opt_set() appends to the list of options.  The un-fixed-up option
> remains in the list.  qemu_opt_unset() could fix that, but it asserts
> opts_accepts_any() for unclear reasons.  git-blame points to Kevin.
it would be cleaner to unset it but it works event without unsetting it,
since qemu_opt_set...() adds to tail and qemu_opt_get...() finds options
from tail to head.

Nevertheless, Kevin do you recall reasons for assert in 0dd6c526:

int qemu_opt_unset(QemuOpts *opts, const char *name)
...
    assert(opts_accepts_any(opts));

would it be ok if I remove it?

> 
> Have you considered qemu_opt_set_number()?
it was code left from v6 when I didn't know about it. Sorry, I'll
use it instead.

> 
> If this "need a default suffix" pattern exists elsewhere, we should
> consider extending QemuOptDesc to cover it.
I haven't seen/don't recall need for it anywhere else, but it would be
cleanest solution. But it would introduce temptation for users
to shrug off suffixes which is wrong in my opinion. -m 1024 is confusing
unless you know that it's in Mb.

it would be better not to introduce mechanism, that would allow to do such
thing in favor of explicit suffixes.

> 
> > +
> > +                sz = QEMU_ALIGN_UP(qemu_opt_get_size(opts, "mem", ram_size),
> > +                                   8192);
> > +                /* compatibility behaviour for case "-m 0" */
> > +                if (sz == 0) {
> > +                    sz = DEFAULT_RAM_SIZE * 1024 * 1024;
> > +                }
> > +
> 
> Yes, this is needed.  Our command line is bonkers.
> 
> >                  ram_size = sz;
> >                  if (ram_size != sz) {
> >                      fprintf(stderr, "qemu: ram size too large\n");
> >                      exit(1);
> >                  }
> > +                /* store aligned value for future use */
> > +                qemu_opt_set_number(opts, "mem", ram_size);
> 
> Here, you use qemu_opt_set_number().
> 
> Again, this appends to the list, and leaves the non-aligned value in.
it's not an issue since the last appended opt is used in qemu_opt_get_size().

> 
> > +
> > +                sz = qemu_opt_get_size(opts, "maxmem", ram_size);
> > +                if (sz < ram_size) {
> > +                    qemu_opt_set_number(opts, "maxmem", ram_size);
> > +                }
> >                  break;
> >              }
> 
> Looks like you want to fix up something like "-m 1024", so that maxmem
> stays equal to mem.  I'm afraid you also "fix" user errors like "-m
> mem=1024M,maxmem=512M".
Perhaps it would be better to bail out with error here.

> 
> If you refrain from putting defaults into opts, you can distinguish the
> cases "user didn't specify maxmem, so assume mem", and "user specified
> maxmem, so check it's >= mem".
So foar, there is no point in distinguishing above cases,
since maxmem <= mem is invalid value and hotplug should be disabled.
So setting default maxmem to mem or anything less effectively disables hotplug.

> 
> >  #ifdef CONFIG_TPM
> > @@ -4029,11 +4083,6 @@ int main(int argc, char **argv, char **envp)
> >          exit(1);
> >      }
> >  
> > -    /* init the memory */
> > -    if (ram_size == 0) {
> > -        ram_size = DEFAULT_RAM_SIZE * 1024 * 1024;
> > -    }
> > -
> >      if (qemu_opts_foreach(qemu_find_opts("device"), device_help_func, NULL, 0)
> >          != 0) {
> >          exit(0);

Thanks for review!

-- 
Regards,
  Igor