This patchset mainly converts strut resource's sibling list from singly linked list to doubly linked list, list_head. This is suggested by Andrew. Since I need a reversed searching on iomem_resource's IORESOURCE_SYSTEM_RAM children, the old singly linked list way makes the code in v1 post really ugly.
With this change, we only need one simple list_for_each_entry_reverse() to do reversed iteration on sibling list. The relevant codes in kernel/resource.c are more readable since those dazzling pointer operation codes for singly linked list are replaced. With the help of list_head, in patch 0002 we can have a very simple walk_system_ram_res_rev(). And in patch 0003, will use it to search available system RAM region for kexec_buffer of kexec_file from top to down, just like we have been doing all along in kexec loading which is done in kexec-tools utility. Note: This patchset passed testing on my kvm guest, x86_64 arch with network enabling. The thing we need pay attetion to is that a root resource's child member need be initialized specifically with LIST_HEAD_INIT() if sttically defined or INIT_LIST_HEAD() for dynamically definition. Here Just like we do for iomem_resource/ioport_resource, or the change in get_pci_domain_busn_res(). And there are two places of change I am not very sure. One is in drivers/hv/vmbus_drv.c, the other is in drivers/pci/host/vmd.c. So will invite experts on these areas to help review. V2 post and discussions can be found here: https://lkml.org/lkml/2018/4/7/169 Remaining issue: Rob raised issue that if we can make an common tree struct and helpers defined on top of list_head or a new struct, quote his saying as below. I didn't do much investigation, we may have a new struct like struct tlist { void *parent; struct list_head sibling; struct list_head child; } Since I have some rhel dev things right now, may consider this later, put it in my TODO list. In kernel, like task_struct, task_group, they all have this kind of tree list, and have used list_head. If anyone is interested, feel free to have a try on this. ========== The DT struct device_node also has the same tree structure with parent, child, sibling pointers and converting to list_head had been on the todo list for a while. ACPI also has some tree walking functions (drivers/acpi/acpica/pstree.c). Perhaps there should be a common tree struct and helpers defined either on top of list_head or a new struct if that saves some size. ========== Changelog: v2->v3: Rename resource functions first_child() and sibling() to resource_first_chils() and resource_sibling(). Dan suggested this. Move resource_first_chils() and resource_sibling() to linux/ioport.h and make them as inline function. Rob suggested this. Accordingly add linux/list.h including in linux/ioport.h, please help review if this bring efficiency degradation or code redundancy. The change on struct resource {} bring two pointers of size increase, mention this in git log to make it more specifically, Rob suggested this. v1->v2: Use list_head instead to link resource siblings. This is suggested by Andrew. Rewrite walk_system_ram_res_rev() after list_head is taken to link resouce siblings. Baoquan He (3): resource: Use list_head to link sibling resource resource: add walk_system_ram_res_rev() kexec_file: Load kernel at top of system RAM if required arch/sparc/kernel/ioport.c | 2 +- drivers/gpu/drm/drm_memory.c | 3 +- drivers/gpu/drm/gma500/gtt.c | 5 +- drivers/hv/vmbus_drv.c | 52 +++---- drivers/input/joystick/iforce/iforce-main.c | 4 +- drivers/nvdimm/e820.c | 2 +- drivers/nvdimm/namespace_devs.c | 6 +- drivers/nvdimm/nd.h | 5 +- drivers/of/address.c | 4 +- drivers/parisc/lba_pci.c | 4 +- drivers/pci/host/vmd.c | 8 +- drivers/pci/probe.c | 2 + drivers/pci/setup-bus.c | 2 +- include/linux/ioport.h | 20 ++- kernel/kexec_file.c | 2 + kernel/resource.c | 221 ++++++++++++++++------------ 16 files changed, 193 insertions(+), 149 deletions(-) -- 2.13.6
