Обычно вы должны сами делать библиотечный клей ...
void get_channel_md5( GIOChannel* channel, unsigned char output[16] )
{
md5_context ctx;
gint64 fileSize = <get file size somehow?>;
gint64 filePos = 0ll;
gsize bufferSize = g_io_channel_get_buffer_size( channel );
void* buffer = malloc( bufferSize );
md5_starts( &ctx );
// hash buffer at a time:
while ( filePos < fileSize )
{
gint64 size = fileSize - filePos;
if ( size > bufferSize )
size = bufferSize;
g_io_channel_read( channel, buffer );
md5_update( &ctx, buffer, (int)size );
filePos += bufferSize;
}
free( buffer );
md5_finish( &ctx, output );
}