Re: [Qemu-devel] [PATCH] replace functions which are only available in glib-2.24

[Paolo Bonzini]

On 15/05/2018 09:42, Markus Armbruster wrote:
> Olaf Hering <address@hidden> writes:
> 
>> Currently the minimal supported version of glib is 2.22.
>> Since testing is done with a glib that claims to be 2.22, but in fact
>> has APIs from newer version of glib, this bug was not caught during
>> submit of the patch referenced below.
>>
>> Replace g_realloc_n, which is available only since 2.24, with g_renew.
> 
> We're about to bump our required GLib version to 2.34.  See
> https://lists.gnu.org/archive/html/qemu-devel/2018-05/msg02562.html
> Message-ID: <address@hidden>
> 
> However, the patch may make sense for stable anyway.

It's a good idea even for non-stable.  In the end, g_*alloc*_n are
rarely needed, and almost always g_*new* is better as it provides better
type safety.  I'm queuing the patch, and we should consider adding a
checkpatch rule to suggest not using these functions.

Paolo

>> Fixes commit 418026ca43 ("util: Introduce vfio helpers")
>>
>> Signed-off-by: Olaf Hering <address@hidden>
>> ---
>>
>> This must go into stable-2.12.
> 
> Please see docs/devel/stable-process.rst for how to get a patch into a
> stable release.
> 
>>  util/vfio-helpers.c | 6 ++----
>>  1 file changed, 2 insertions(+), 4 deletions(-)
>>
>> diff --git a/util/vfio-helpers.c b/util/vfio-helpers.c
>> index 006674c916..5fd4f5f212 100644
>> --- a/util/vfio-helpers.c
>> +++ b/util/vfio-helpers.c
>> @@ -522,8 +522,7 @@ static IOVAMapping *qemu_vfio_add_mapping(QEMUVFIOState 
>> *s,
>>  
>>      assert(index >= 0);
>>      s->nr_mappings++;
>> -    s->mappings = g_realloc_n(s->mappings, sizeof(s->mappings[0]),
>> -                              s->nr_mappings);
>> +    s->mappings = g_renew(IOVAMapping *, s->mappings, s->nr_mappings);
> 
> I'm afraid this switches from allocating a bunch of IOVAMapping to a
> bunch of IOVAMapping *.  My gcc duly warns.
> 
>>      insert = &s->mappings[index];
>>      shift = s->nr_mappings - index - 1;
>>      if (shift) {
>> @@ -577,8 +576,7 @@ static void qemu_vfio_undo_mapping(QEMUVFIOState *s, 
>> IOVAMapping *mapping,
>>      memmove(mapping, &s->mappings[index + 1],
>>              sizeof(s->mappings[0]) * (s->nr_mappings - index - 1));
>>      s->nr_mappings--;
>> -    s->mappings = g_realloc_n(s->mappings, sizeof(s->mappings[0]),
>> -                              s->nr_mappings);
>> +    s->mappings = g_renew(IOVAMapping *, s->mappings, s->nr_mappings);
> 
> Likewise.
> 
>>  }
>>  
>>  /* Check if the mapping list is (ascending) ordered. */