Re: [Qemu-devel] [PATCH] Do not use slow [*] expansion for GPIO creation

["Daniel P. Berrange" <berrange@redhat.com>]

On Wed, Jul 29, 2015 at 03:55:14PM +0300, Pavel Fedin wrote:
> Expansion of [*] suffix is very slow because index expansion is done using
> trial and error strategy, starting every time from zero and retrying with
> the next index until insertion succeeds. With large number of already added
> properties this process takes huge amount of time (O(n^2) complexity).
> 
> Some architectures (like ARM) use very large amount of IRQ pins in interrupt
> controller models. This flaw makes machine startup extremely slow
> (~20 seconds for ARM64 with 32 CPUs. This patch decreases this time down to
> ~10 seconds.
> 
> Signed-off-by: Pavel Fedin <p.fedin@samsung.com>
> ---
>  hw/core/qdev.c | 29 ++++++++++++++++++++++++-----
>  1 file changed, 24 insertions(+), 5 deletions(-)
> 
> diff --git a/hw/core/qdev.c b/hw/core/qdev.c
> index b2f404a..d285784 100644
> --- a/hw/core/qdev.c
> +++ b/hw/core/qdev.c
> @@ -25,6 +25,8 @@
>     inherit from a particular bus (e.g. PCI or I2C) rather than
>     this API directly.  */
>  
> +#include <glib/gprintf.h>
> +
>  #include "hw/qdev.h"
>  #include "hw/fw-path-provider.h"
>  #include "sysemu/sysemu.h"
> @@ -415,15 +417,24 @@ static NamedGPIOList *qdev_get_named_gpio_list(DeviceState *dev,
>  void qdev_init_gpio_in_named(DeviceState *dev, qemu_irq_handler handler,
>                               const char *name, int n)
>  {
> -    int i;
> +    int i, l;
>      NamedGPIOList *gpio_list = qdev_get_named_gpio_list(dev, name);
> -    char *propname = g_strdup_printf("%s[*]", name ? name : "unnamed-gpio-in");
> +    char *propname;
>  
>      assert(gpio_list->num_out == 0 || !name);
> +
> +    if (!name) {
> +        name = "unnamed-gpio-in";
> +    }
> +    l = strlen(name);
> +    propname = g_malloc(l + 13); /* 10 characters for UINT_MAX plus "[]" */
> +    memcpy(propname, name, l);

Please don't do manual string length calculations in combination with
unbounded sprintf calls. It is a recipe for future security bugs.

> +
>      gpio_list->in = qemu_extend_irqs(gpio_list->in, gpio_list->num_in, handler,
>                                       dev, n);
>  
>      for (i = gpio_list->num_in; i < gpio_list->num_in + n; i++) {
> +        g_sprintf(&propname[l], "[%u]", i);

Replace this with

    gchar *propname = g_strdup_printf("%s[%u]", name, i)

>          object_property_add_child(OBJECT(dev), propname,
>                                    OBJECT(gpio_list->in[i]), &error_abort);

    g_free(propname);

>      }
> @@ -440,14 +451,21 @@ void qdev_init_gpio_in(DeviceState *dev, qemu_irq_handler handler, int n)
>  void qdev_init_gpio_out_named(DeviceState *dev, qemu_irq *pins,
>                                const char *name, int n)
>  {
> -    int i;
> +    int i, l;
>      NamedGPIOList *gpio_list = qdev_get_named_gpio_list(dev, name);
> -    char *propname = g_strdup_printf("%s[*]", name ? name : "unnamed-gpio-out");
> +    char *propname;
>  
>      assert(gpio_list->num_in == 0 || !name);
> -    gpio_list->num_out += n;
> +
> +    if (!name) {
> +        name = "unnamed-gpio-out";
> +    }
> +    l = strlen(name);
> +    propname = g_malloc(l + 13); /* 10 characters for UINT_MAX plus "[]" */
> +    memcpy(propname, name, l);

Same again here.

>  
>      for (i = 0; i < n; ++i) {
> +        g_sprintf(&propname[l], "[%u]", gpio_list->num_out + i);
>          memset(&pins[i], 0, sizeof(*pins));
>          object_property_add_link(OBJECT(dev), propname, TYPE_IRQ,
>                                   (Object **)&pins[i],
> @@ -456,6 +474,7 @@ void qdev_init_gpio_out_named(DeviceState *dev, qemu_irq *pins,
>                                   &error_abort);
>      }
>      g_free(propname);
> +    gpio_list->num_out += n;
>  }

Regards,
Daniel
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