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Re: [Qemu-ppc] [PATCH v2 10/18] hw/nvram/fw_cfg: Add reboot_timeout to F

From: Laszlo Ersek
Subject: Re: [Qemu-ppc] [PATCH v2 10/18] hw/nvram/fw_cfg: Add reboot_timeout to FWCfgState
Date: Fri, 8 Mar 2019 12:04:09 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1

Hi Phil,

On 03/08/19 02:32, Philippe Mathieu-Daudé wrote:
> Due to the contract interface of fw_cfg_add_file(), the
> 'reboot_timeout' data has to be valid for the lifetime of the
> FwCfg object. For this reason it is copied on the heap with
> memdup().
> The object state, 'FWCfgState', is also meant to be valid during the
> lifetime of the object.
> Move the 'reboot_timeout' in FWCfgState to achieve the same purpose.
> Doing so we avoid a memory leak.
> Signed-off-by: Philippe Mathieu-Daudé <address@hidden>
> ---
>  hw/nvram/fw_cfg.c         | 4 +++-
>  include/hw/nvram/fw_cfg.h | 2 ++
>  2 files changed, 5 insertions(+), 1 deletion(-)

Currently, there is no memory leak. Right now, the leak is theoretical,
and it would depend on the fw_cfg object being actually destroyed.

I think armoring the fw_cfg implementation for such lifetime actions is
valuable. But, that definitely belongs to its own series, in my opinion.

In the "hw/nvram/fw_cfg.c" file, I count:

(a) two "specific purpose" g_memdup() calls, namely in
fw_cfg_bootsplash() and in fw_cfg_reboot();

(b) one "generic purpose" g_memdup() call, namely in fw_cfg_add_string();

(c) two "generic purpose" g_malloc() calls, namely in fw_cfg_add_i16(),
fw_cfg_add_i32(), and fw_cfg_add_i64(). (The one in fw_cfg_modify_i16()
does not matter here because the previous blob is freed in that function.)

Your series deals with (a), namely with fw_cfg_reboot() in this patch,
and with fw_cfg_bootsplash() in the next one.

Your series deals with neither (b) nor (c). The
fw_cfg_add_(string|i16|i32|i64) functions are called from a bunch of
places however, so if we really intend *not* to leak those copies upon
fw_cfg destruction, then we'll have to track all of them dynamically, in
a list for example.

(And that necessitates a separate series for this topic even more.)

In turn, once we add dynamic tracking, for those blobs that the
fw_cfg_add_(string|i16|i32|i64) functions allocate internally -- as they
are advertized to do --, then we might as well use the same tracking
infrastructure for (a). In other words, it should not be necessary to
add the specific fields "reboot_timeout" and "boot_splash" to FWCfgState.


> diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c
> index b73a591eff..182d27f59a 100644
> --- a/hw/nvram/fw_cfg.c
> +++ b/hw/nvram/fw_cfg.c
> @@ -250,7 +250,9 @@ static void fw_cfg_reboot(FWCfgState *s)
>          }
>      }
> -    fw_cfg_add_file(s, "etc/boot-fail-wait", g_memdup(&rt_val, 4), 4);
> +    s->reboot_timeout = rt_val;
> +    fw_cfg_add_file(s, "etc/boot-fail-wait",
> +                    &s->reboot_timeout, sizeof(s->reboot_timeout));
>  }
>  static void fw_cfg_write(FWCfgState *s, uint8_t value)
> diff --git a/include/hw/nvram/fw_cfg.h b/include/hw/nvram/fw_cfg.h
> index 828ad9dedc..99f6fafcaa 100644
> --- a/include/hw/nvram/fw_cfg.h
> +++ b/include/hw/nvram/fw_cfg.h
> @@ -53,6 +53,8 @@ struct FWCfgState {
>      dma_addr_t dma_addr;
>      AddressSpace *dma_as;
>      MemoryRegion dma_iomem;
> +
> +    uint32_t reboot_timeout;
>  };
>  struct FWCfgIoState {

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