Contribute/BiteSizedTasks

API conversion

• Look for uses of malloc, and convert them to either g_malloc, g_new (more rarely g_try_malloc or g_try_new if a lot of memory is being allocated). Likewise, convert calloc to either g_new0 or g_try_new0. Drop return value checks unless using g_try_new/g_try_new0.
• Associate external libraries with the object files that actually use them
• For all "QEMUTimer*" variables that are initialized with timer_new, change them to "QEMUTimer" and initialize them with timer_init. Drop any timer_free calls (there aren't many, so this patch would fix small memory leaks too). (not quite bite-sized).
• Replace calls to functions named cpu_physical_memory_* with address_space_*.
• Change net/socket.c to use the functions in include/qemu/sockets.h instead of parse_host_port/bind/connect/listen.
• Change QemuMutex and QemuCond to CompatGMutex and CompatGCond (these are the same as GMutex and GCond, just with a different type). With this change, qemu_mutex_init/qemu_cond_init becomes optional for global variables.
• Change get_ticks_per_sec() calls to just use the NANOSECONDS_PER_SECOND constant.
• Remove macros IO_READ_PROTO and IO_WRITE_PROTO.
• Replace calls to object_child_foreach() with object_child_foreach_recursive() when applicable.
• Change basename and dirname to g_path_get_basename() and g_path_get_dirname() respectively.
• Devices which create MemoryRegions with the old_mmio accessors should be converted to new style mmio accessors.

Header cleanups

• avoid including include/exec/exec-all.h from other headers.
• avoid including files from include/exec/cpu-common.h.

Device models

• Include SDState by value instead of allocating it in sd_init (hw/sd/).
• Look for invocations of qemu_system_reset_request() in hw/. Whenever they correspond to some kind of watchdog that has triggered, change to watchdog_perform_action().

Error checking

• Add checks for NULL return value to uses of load_image_targphys, qemu_find_file.
• Add checks for negative return value to uses of get_image_size, event_notifier_init, msix_init.
• Use qemu_strtol/qemu_strtoul/qemu_strtoll/qemu_strtoull more.

Device lifecycle

• IDE uses qemu_add_vm_change_state_handler() without a corresponding qemu_del_vm_change_state_handler(). This means hot unplugging an AHCI PCI adapter results in a dangling change state handler and could lead to a crash.

Large frames

• The following functions have very large stack frames (as obtained with -Wstack-usage=16383), mostly due to huge arrays. Make the stack array smaller and allocate on the heap in the rare case that the data does not fit in the small array:

hw/dma/xilinx_axidma.c               stream_process_mem2s             16480 bytes
hw/net/virtio-net.c                  virtio_net_receive               16544 bytes
net/tap.c                            net_init_tap                     16752 bytes
block/vmdk.c                         vmdk_write_cid.isra.8            20544 bytes
hw/display/vmware_vga.c              vmsvga_fifo_run                  20688 bytes
hw/virtio/virtio.c                   virtqueue_pop                    24768 bytes
hw/net/virtio-net.c                  virtio_net_flush_tx              32928 bytes
hw/virtio/virtio.c                   qemu_get_virtqueue_element       49216 bytes
hw/virtio/virtio.c                   qemu_put_virtqueue_element       49216 bytes
hw/net/opencores_eth.c               open_eth_start_xmit              65664 bytes
hw/arm/nseries.c                     n8x0_init                        65728 bytes
net/net.c                            nc_sendv_compat                  69680 bytes
net/socket.c                         net_socket_send                  69712 bytes

Dead code removal

• hw/display contains files named *_template.h. These are included many times with different values of the DEPTH macro. However, only the DEPTH == 32 case is used. Remove support for DEPTH != 32 in the template headers and in the file that include them.
• Look for functions that are named *_exit or *_exitfn in hw/ and that return int. They should all return zero. Make them return void, and remove the checks for the callers.
• Once the above change is done, remove the "Error **" argument from functions named *_unrealize in hw/
• Remove bdrv_aio_multiwrite() since virtio-blk no longer uses it and the only remaining caller, qemu-io, is for testing only

Tracing

• Add tracepoints. All functions that are named something_helper, and all functions mentioned in MemoryRegionOps are good candidates.

Bitrot prevention

• Files with conditional debug statements should ensure that the printf is always compiled, and merely hidden behind if (0) when not debugging, rather than #ifdef'd out. This prevents bitrot of the format string of the debug statement. See commit c691320faa6 for an example. Or, go one step further and convert the debug statements to tracepoints.