Re: [PATCH v1 7/9] plugins: add API to return a name for a IO device - Philippe Mathieu-Daudé

From: "Philippe Mathieu-Daudé" <philmd@redhat.com>
To: "Emilio G. Cota" <cota@braap.org>,
	"Alex Bennée" <alex.bennee@linaro.org>
Cc: robert.foley@linaro.org, qemu-devel@nongnu.org,
	robhenry@microsoft.com, aaron@os.amperecomputing.com,
	peter.puhov@linaro.org, kuhn.chenqun@huawei.com
Subject: Re: [PATCH v1 7/9] plugins: add API to return a name for a IO device
Date: Mon, 8 Jun 2020 08:20:01 +0200	[thread overview]
Message-ID: <12dd5c71-01c9-3d7f-7299-80eb928c7f2e@redhat.com> (raw)
In-Reply-To: <20200608034504.GA3619843@sff>

On 6/8/20 5:45 AM, Emilio G. Cota wrote:
> On Tue, Jun 02, 2020 at 16:46:22 +0100, Alex BennÃƒÂ©e wrote:
>> This may well end up being anonymous but it should always be unique.
>>
>> Signed-off-by: Alex BennÃƒÂ©e <alex.bennee@linaro.org>
>> ---
>>  include/qemu/qemu-plugin.h |  5 +++++
>>  plugins/api.c              | 18 ++++++++++++++++++
>>  2 files changed, 23 insertions(+)
>>
>> diff --git a/include/qemu/qemu-plugin.h b/include/qemu/qemu-plugin.h
>> index bab8b0d4b3a..43c6a9e857f 100644
>> --- a/include/qemu/qemu-plugin.h
>> +++ b/include/qemu/qemu-plugin.h
>> @@ -335,6 +335,11 @@ struct qemu_plugin_hwaddr *qemu_plugin_get_hwaddr(qemu_plugin_meminfo_t info,
>>  bool qemu_plugin_hwaddr_is_io(const struct qemu_plugin_hwaddr *haddr);
>>  uint64_t qemu_plugin_hwaddr_device_offset(const struct qemu_plugin_hwaddr *haddr);
>>  
>> +/*
>> + * Returns a string representing the device. Plugin must free() it
>> + */
>> +char * qemu_plugin_hwaddr_device_name(const struct qemu_plugin_hwaddr *haddr);
>> +
>>  typedef void
>>  (*qemu_plugin_vcpu_mem_cb_t)(unsigned int vcpu_index,
>>                               qemu_plugin_meminfo_t info, uint64_t vaddr,
>> diff --git a/plugins/api.c b/plugins/api.c
>> index bbdc5a4eb46..3c73de8c1c2 100644
>> --- a/plugins/api.c
>> +++ b/plugins/api.c
>> @@ -303,6 +303,24 @@ uint64_t qemu_plugin_hwaddr_device_offset(const struct qemu_plugin_hwaddr *haddr
>>      return 0;
>>  }
>>  
>> +char * qemu_plugin_hwaddr_device_name(const struct qemu_plugin_hwaddr *haddr)
>> +{
>> +#ifdef CONFIG_SOFTMMU
>> +    if (haddr && haddr->is_io) {
>> +        MemoryRegionSection *mrs = haddr->v.io.section;
>> +        if (!mrs->mr->name) {
>> +            return g_strdup_printf("anon%08lx", 0xffffffff & (uintptr_t) mrs->mr);
>> +        } else {
>> +            return g_strdup(mrs->mr->name);
>> +        }
>> +    } else {
>> +        return g_strdup("RAM");
>> +    }
>> +#else
>> +    return g_strdup("Invalid");
>> +#endif
>> +}
> 
> I'd rather use asprintf(3) and strdup(3) here, so that plugins don't
> have to worry about glib, and on the QEMU side we don't have to worry
> about plugins calling free() instead of g_free().

It might make sense, but it should be documented in
include/qemu/qemu-plugin.h or docs/devel/tcg-plugins.rst.

> 
> Or given that this doesn't look perf-critical, perhaps an easier way out
> is to wrap the above with:
> 
> char *g_str = above();
> char *ret = strdup(g_str);
> g_free(g_str);

free() ;)

> return ret;
> 
> Not sure we should NULL-check ret, since I don't know whether
> mrs->mr->name is guaranteed to be non-NULL.
> 
> Thanks,
> 		Emilio
> 