Re: [edk2-devel] [PATCH 05/11] OvmfPkg/XenBusDxe: Construct paths without allocation

["Laszlo Ersek" <lersek@redhat.com>]

On 09/16/19 17:39, Laszlo Ersek wrote:
> On 09/13/19 16:50, Anthony PERARD wrote:
>> When doing an action with a path and subpath in the xenstore,
>> XenStoreJoin is called to generate "$path/$subpath". But this function
>> do an allocation of memory which isn't necessary. Instead we will
>> construct the path with WRITE_REQUEST and data used to generate the
>> path will be copied directly to the xenstore shared ring.
>>
>> Also change WRITE_REQUEST.Len type, it only contain sizes and doesn't
>> need to be exactly 32bits.
>>
>> Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=2190
>> Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
>> ---
>>  OvmfPkg/XenBusDxe/XenStore.c | 78 +++++++++++++++++++++---------------
>>  1 file changed, 46 insertions(+), 32 deletions(-)
>>
>> diff --git a/OvmfPkg/XenBusDxe/XenStore.c b/OvmfPkg/XenBusDxe/XenStore.c
>> index 7b71dc156d..ca7be12d68 100644
>> --- a/OvmfPkg/XenBusDxe/XenStore.c
>> +++ b/OvmfPkg/XenBusDxe/XenStore.c
>> @@ -53,7 +53,7 @@
>>  
>>  typedef struct {
>>    CONST VOID  *Data;
>> -  UINT32      Len;
>> +  UINTN       Len;
>>  } WRITE_REQUEST;
>>  
>>  /* Register callback to watch subtree (node) in the XenStore. */
>> @@ -260,6 +260,35 @@ XenStoreFindWatch (
>>    return NULL;
>>  }
>>  
>> +/**
>> +  Fill the first three slots of a WRITE_REQUEST array.
>> +
>> +  When those three slots are concatenated to generate a string, the resulting
>> +  string will be "$Path\0" or "$Path/$SubPath\0" if SubPath is provided.
>> +**/
>> +STATIC
>> +VOID
>> +XenStorePrepareWriteRequest (
>> +  IN OUT WRITE_REQUEST *WriteRequest,

(6) I think this could be just OUT -- we start by zeroing it out.

>> +  IN     CONST CHAR8   *Path,
>> +  IN     CONST CHAR8   *SubPath OPTIONAL
>> +  )
>> +{
>> +  SetMem(WriteRequest, 3 * sizeof (WRITE_REQUEST), 0);

Thanks
Laszlo