Re: [Qemu-devel] [PATCH 2/2] vl: convert -m to QemuOpts

[Laszlo Ersek]

comments below

On 02/06/14 09:16, Igor Mammedov wrote:
> Adds option to -m
>  "mem" - startup memory amount
> 
> For compatibility with legacy CLI if suffix-less number is passed,
> it assumes amount in Mb.
> 
> Otherwise user is free to use suffixed number using suffixes b,k/K,M,G
> 
> Signed-off-by: Igor Mammedov <address@hidden>
> Signed-off-by: Paolo Bonzini <address@hidden>
> ---
>  qemu-options.hx |    7 +++++--
>  vl.c            |   53 ++++++++++++++++++++++++++++++++++++++++++-----------
>  2 files changed, 47 insertions(+), 13 deletions(-)
> 
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 56e5fdf..4d7ef52 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -210,8 +210,11 @@ 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\n"
> +    "                configure guest RAM\n"

"configure guest RAM size"

> +    "                mem: initial amount of guest memory (default: "
> +    stringify(DEFAULT_RAM_SIZE) "Mb)\n",

I wonder if it should rather say "MB" -- small "b" has this "bits"
connotation for me. But I could be wrong.

Also, again, I believe explaining the default used to mean something
else, but I'm OK with that part as-is.

> +    QEMU_ARCH_ALL)
>  STEXI
>  @item -m @var{megs}
>  @findex -m
> diff --git a/vl.c b/vl.c
> index 7f2595c..fe5dae3 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -532,6 +532,20 @@ static QemuOptsList qemu_msg_opts = {
>      },
>  };

(this could conflict with Alan's series -- modifies the same spot)

> +static QemuOptsList qemu_mem_opts = {
> +    .name = "memory-opts",
> +    .implied_opt_name = "mem",
> +    .head = QTAILQ_HEAD_INITIALIZER(qemu_mem_opts.head),
> +    .merge_lists = true,

OK, so we've set merge_list to true here as well, same as for "machine".
Further support for simplifying qemu_find_opts_singleton(); see patch #1.

> +    .desc = {
> +        {
> +            .name = "mem",
> +            .type = QEMU_OPT_SIZE,

QEMU_OPT_SIZE implies (in parse_option_size()) that "no suffix" means
"unit==byte" (); I'll check lower down how that's solved.

> +        },
> +        { /* end of list */ }
> +    },
> +};
> +
>  /**
>   * Get machine options
>   *
> @@ -2868,6 +2882,7 @@ int main(int argc, char **argv, char **envp)
>      };
>      const char *trace_events = NULL;
>      const char *trace_file = NULL;
> +    const ram_addr_t default_ram_size = DEFAULT_RAM_SIZE * 1024 * 1024;

I'd feel safer if the multiplications were done in ram_addr_t. Currently
they are done in "int". It's unlikely that we'll make 2GB+ the default
ram size, but still.

>  
>      atexit(qemu_run_exit_notifiers);
>      error_set_progname(argv[0]);
> @@ -2906,6 +2921,7 @@ 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();
>  
> @@ -2921,7 +2937,7 @@ 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;
>      snapshot = 0;
>      cyls = heads = secs = 0;
>      translation = BIOS_ATA_TRANSLATION_AUTO;
> @@ -3198,16 +3214,32 @@ 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 *mem_str;
>  
> -                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);

This can set "opts" to NULL if parsing fails, and then the
qemu_opt_get() just below will SIGSEGV. You need to check if "opts"
becomes NULL here, and exit if so (see other calls to qemu_opts_parse()
in main()).

In particular, see commit f46e720a.

Also, unfortunately, this conversion kind of relaxes the error checking
that happens during parsing. The pre-patch version ends up in
strtosz_suffix_unit(), which rejects the empty string, for example. The
new version, which ends up in parse_option_size(), is not that smart
about strtod(). I think it will simply return zero for

  -m mem=""

However it's not the fault of this patch.

> +
> +                mem_str = qemu_opt_get(opts, "mem");
> +                if (!mem_str) {
> +                    fprintf(stderr, "qemu: invalid -m option, missing "
> +                            " 'mem' option\n");

Double space. (There's one at the end of the first string literal, and
another at the beginning of the second literal.)

>                      exit(1);
>                  }
> -                sz = QEMU_ALIGN_UP((uint64_t)value, 8192);
> +
> +                sz = qemu_opt_get_size(opts, "mem", ram_size);
> +
> +                /* Fix up legacy suffix-less format */
> +                if (g_ascii_isdigit(mem_str[strlen(mem_str) - 1])) {

Undefined behavior if mem_str is the emptry string. (I think it is
possible, but I didn't test it.)

> +                    sz <<= 20;
> +                }

We could check for overflow here, if we wanted.

> +
> +                /* backward compatibility behaviour for case "-m 0" */
> +                if (sz == 0) {
> +                    sz = default_ram_size;
> +                }
> +
> +                sz = QEMU_ALIGN_UP(sz, 8192);
>                  ram_size = sz;
>                  if (ram_size != sz) {
>                      fprintf(stderr, "qemu: ram size too large\n");
> @@ -4056,10 +4088,9 @@ int main(int argc, char **argv, char **envp)
>          exit(1);
>      }
>  
> -    /* init the memory */
> -    if (ram_size == 0) {
> -        ram_size = DEFAULT_RAM_SIZE * 1024 * 1024;
> -    }
> +    /* store value for the future use */
> +    qemu_opt_set_number(qemu_find_opts_singleton("memory-opts"),
> +                        "mem", ram_size);

Slight possibility here to overflow the int64_t "val" parameter with the
potentially uint64_t "ram_size" argument. I guess we don't care.

Also, I wonder what happens when we have passed a non-default memory
size on the command line. In that case, qemu_opt_set_number() seems to
create a second QemuOpt here. I guess that's maybe expected though?

>  
>      if (qemu_opts_foreach(qemu_find_opts("device"), device_help_func, NULL, 
> 0)
>          != 0) {
> 

It's your call what you'd like to address from the above.

Thanks
Laszlo